Vorshlag Low Buck 1992 Corvette NASA TTC Project Build Thread, aka: DANGER ZONE

nocones wrote: Thanks for the information. What do you think of the deep wrap around bolsters of a circle track seat (kirkey 56lw type) vs the smaller side bolsters and shoulder support of a "road race" seat (ultrashield rallysport style) vs a drag race type seat with the shallow bolsters and no shoulders (ultrashield spec Miata) Thanks keep up the good work.

They all have their uses, for sure. I'm not a fan of the little spindly drag race seats - they typically have almost no lateral support. The "Wrap around" style can really keep you in place, but they don't work well for fat.... err.... healthy eaters. :D The "Road Race" seats can help with shoulder placement but tend to lack the serious rib protecting/gut grabbing lateral support of the former style.

In a Miata... you don't have enough room to worry about too many choices. The drag style/minimalist seats are about the only thing that fits. These are TIGHT confines you are working with and your choices just really diminish. Being the most popular sports car ever made there are plenty of examples of what fits and what doesn't...

Good luck,

Terry @ Vorshlag

Actually will be going in a tube frame MG midget but very similar space concerns as a Miata. Sounds like of the aluminum options you like the circle track seats assuming you can find one that fits you/the car. I think the Kirkey LW may be in my future. Thanks again I will definately follow this build moving forward. I've noticed a lot of the "shop" builds are not really interactive but seems that you guys really embrace what observers can offer.

I guessed the car based on the thread title.

Welcome Terry Fair. I enjoy your writing and I enjoy following along on your builds. Glad you found a workaround for posting on GRM.

dyintorace wrote: Then you guys have some of the nicest damn home garages I've ever seen in my life!

Meh. I've got several friends that have "out garaged" me. :/

I designed this house AROUND a big garage, so it was no accident. Spec'd it with 12'6" ceilings, a flat floor, room for a 2-post lift (with a thicker slab), built all of the custom tables and shelving, added some pallet racks, custom built a tire rack, rolled on the epoxy flooring myself, etc.

It was a LOT of work that took place over at least a year. And we ran Vorshlag out of here, years ago, then left the 2-post lift and the tire rack when we moved into a bigger commercial space.

Lately it has reverted back to just being a home garage, with nothing more than car storage going on. Me and a couple of buddies did build a Chump/LeMons car in here a couple of years ago (white '99 Firebird with 3.8L Buick V6 shown below), but that's about it.

My wife parks her daily driver (BMW 740) inside and I've usually got 4 or 5 other "project cars in waiting" stashed here. My two trucks and our enclosed trailer all get stuck outside - not enough room.

There's room on our property for a bigger, detached building. Some day...

nocones wrote: Actually will be going in a tube frame MG midget but very similar space concerns as a Miata. Sounds like of the aluminum options you like the circle track seats assuming you can find one that fits you/the car. I think the Kirkey LW may be in my future...

My go-to Kirkey seat that I used in my hardtop Miata is currently called the 58 Series, Lightweight 20 degree Layback Seat. I usually used it with a full cover and some additional padding glued inside the hips and ribs. It took a twist to get into it with a fixed steering wheel and the top on the car, but it was still easy. FWIW, I'm 6'3" and 250+ lbs.

This is a cool build, and I want to buy a C4 for auto-x and track duty in the not too distant future.

Project Update for January 9th, 2015: The first stage of "initial race prep" for this project is getting down to the wire with the NASA race debut only ONE week away! Let's get caught up on the work we've been knocking on Project DANGER ZONE, our TTC class prepped 1992 Corvette. I had intended this to be a quick update, showing the initial stages of race prep, but I started writing and somehow this post spiraled out of control. It now includes some aero/drag reduction theory, the History of Iron and Steel, a good bit on roll cage tubing and design, some tire analysis, and other random tidbits of tech. If you get bored easily just skip down to the pictures and enjoy.

Safety First, Kids!

There are many Safety Upgrades we want to add to (or repair on) this Corvette during the 2015 season, which are the same for virtually any dedicated road race build. Unfortunately we were pressed for time and won't get them all done before the first race. The Safety list includes: a full roll cage, racing seat install, 6-point racing harness, window nets, full fire extinguisher system, secondary 2.5 pound fire bottle, tow hooks at both ends, tie-down hooks at both ends (for towing), replace the broken windshield, replace the rear hatch glass with Lexan or Plexiglass, and more. That's a lot of parts and work on the "Punch List", but as far as what's "required" for NASA Time Trial, that is much less. We also have some repairs and performance upgrades to tackle, too. We got almost nothing done over the holidays (short weeks, busy on customer cars) so let's see what we can get done in two weeks.

Windshield + Small Aero Improvements

This repair is really a safety upgrade, because you cannot race with a busted windshield. Before I bought the car from Matteucci he had warned me about this problem - it had a lot of big cracks on the passenger side and chunk missing where the OEM rear view mirror attached, with the cracks propagating into the driver's view. The upper right corner of the windshield trim and weatherstrip took a hit when a former owner (ie: The Crackhead) drove it through a barbed wire fence. Matteucci literally found a crack pipe (maybe a meth pipe) in the car after he bought it. So yea, now you understand part of why this was a $3000 running and driving car purchase.

Nasty, broken windshield and trashed weatherstripping has to be replaced

We discussed delaying the windshield replacement because when you install a roll cage it is ALWAYS easier (and often required) to get the front windshield out of the way to access and weld tubes along the front of the cage. In some cars with a fixed rear glass window, that is often removed as well. The cages we built in the two cars below required the windshield to be out. At left is an SCTA legal cage for 200+ mph use on the salt flats, which has more of a "Funny Car" drag racing cage (built per the rules). To weld in the the front tubing gussets requires windshield access. The one at right is a NASA ST3 legal Mustang the the dimple-die gussets and front corner tubes need windshield access - as does a proper paint job on any cage.

We knew we wanted a roll cage in DANGER ZONE (to reduce the "zone of danger"), but with only 2 weeks of time build available after the short holiday weeks between Christmas and New years, and many other items that needed attention, meant only building a 4-point roll bar for this first race. Which meant the windshield didn't need to come out. But it was so cracked that it would never pass tech, so it had to be replaced. And when we go back and finish the full cage, out it will come again!

We called our buddies at Titan Auto Glass and they extracted the old and busted and installed the new hotness. There are normally several windshield choices for most cars, varying in price, but for 24 year old Corvettes there was one - and it was a tick pricy at $260 installed. But hey, can't race with a busted windshield. Going to Lexan is an option but there are more downsides (more costly, harder to install, easily scratched, difficult to use wipers with them, more easily nicked by rocks or tire klag) than upsides (slight weight savings). A two layer, laminated, glass OEM style windshield is preferred by many racers when they have a choice.

The OEM windshield surround rubber weather stripping was a total mess (above right). Matteucci had cut away the bits around the A-pillars when he gutted the interior and the top bit was destroyed by the barbed wire. The crackhead former owner had filled in the missing chunk in the rubber seal with SHOE GOO, and that had to be chiseled away (thanks Titan!).

I wasn't about to put this mangled mess of rubber seals back on, but we needed the top bit of rubber to seal the targa roof panel smoothly along the top of the windshield and I also wanted the seals back in place along the edge of the windshield at the A-pillar. This should help smooth the airflow in a high payoff "Green Zone" of potential drag reduction - the edges of the windshield. Read this NASA Speed News article called "Getting Into The Zones" (page 60 ) written by aero guru Neil Roberts (also read his ThinkFAST Engineering blog for more great articles!) and that will make more sense.

A smooth, new set of weather stripping should help aid the transition from the edge of the windshield (sides and top), reducing drag. We are looking to reduce drag in ALL of the Green areas (again, read Neil's article) on this car, and do so legally. We cannot run NASA events with the windows up, so the door window openings have to stay. We have tried to read the rules to say otherwise, but rule 7.2 of the NASA TT rules is pretty clear:

7.2 Front driver and passenger side fixed/Lexan windows are specifically not permitted unless they are factory installed during the manufacturing of the vehicle. Both front side windows must otherwise be in the down position while on track."

Running the windows UP would be a decrease in drag but it is not allowed in virtually any form of road racing, for safety reasons (easier extraction after a crash). Some drag racing classes and high speed events like Bonneville do allow for side windows, so the silver Subaru we're building the cage for above is getting a full Lexan window package (4 side windows + front and rear windscreens).

Why Terry Needs A Roll Cage

There isn't any additional safety requirements in NASA Time Trial groups than what is called for in HPDE run groups: a Snell SA2010 rated helmet and OEM seat belt, plus a roll bar for convertibles. There isn't supposed to be wheel to wheel contact in TT, but we are running for times and competing for contingency prizes, and many TT racers take it pretty seriously. I won six sets of Hoosier race tires racing in NASA TT3 class in 2014, and these were BIG tires that cost $1710 a set, so there is some decent swag on the line. When you are chasing a TT win you often push the limits and do stupid stuff...

Crap like this

My personal safety record, for the amount of laps I've driven on track, was pretty damned good up until 2014. In 27 years of running on road courses I only had a couple of "offs" that were worth mentioning. I de-beaded a couple of tires in a high speed off at TWS in the late 1980s that curled my hair a bit. A number of times I've had a quick "off and on" that bent a splitter or packed a grill with grass, sure. The stock brake pads came apart and I left Turn 7 at ECR at 90+ mph in 2013 in a stock '13 Mustang. But by far my most memorable off-track experience happened in 2014 (shown above).

After the crash I began wearing a HANS device and fire suit to complement the FIA halo seat, 6-poiont harnesses and roll bar in our TT3 Mustang

I briefly mentioned this in my first post, but it was a pretty spooky incident and I figured it might explain my "overkill" safety requirements for this TT build. After losing brakes at at Road Atlanta at a Global Time Attack event in May 2014, I went off the end of Turn 10A at 150mph, through the gravel trap, and took a big vertical hit coming out of a trap. I got hurt but the car barely took a scratch (splitter came off, was repaired and reinstalled and back on track 2 weeks later, but not with me driving). Even though I had a proper FIA halo seat, good harnesses, and a good roll bar, I wasn't wearing a HANS device. We think this might be why I fractured a vertebrae in my back and broke a rib. After this incident I was in a lot of pain, wearing a back brace for 2 months, and not racing.

Having gone through the crash scenario many times and analyzing frame-by-frame pictures of the crash since, the injury seems to come down to too much "arching" of my back in the impact that broke these bones. A properly worn HANS device would have likely prevented this injury. The "off" happened because I ran out of brake pads, and had been ignoring measured brake caliper temp data of 490°F+ for months. I'm not going to make those series of mistakes again, and I also vowed in 2014 to start racing with better personal safety gear. I was setting a bad example and I needed to do better.

So obviously, after this back-breaking scare I'm taking my safety on track a lot more seriously. I've starting using a HANS device (still haven't picked my favorite model after trying 4 different brands - and I'm about to try the brand new Schroth HANS design, since we are a dealer) and an FIA 3-layer driving suit in all TT events. I am also wearing my harnesses TIGHTER and keeping a much closer eye on things like brake fluid temps and brake pad material depth, so this scenario of failures never happens again.

Roll Cage Is Safety More Than Performance

The steel frame structure of the C4 Corvette. This is a 1984 model

After the personal safety gear, the next most important safety aspect of any race car is the roll cage. This structure is helpful to make the chassis more rigid, sure, but it is there mostly to prevent bodily injury in many types of crashes and "offs". These include single car off track frontal collisions with a barrier (somewhat common), a roll-over crash (very rare), or any car-to-car contact (more common). While a roll cage wouldn't have helped me in my gravel trap "jump" incident at all, there are other types of crashes where it could save your life - and do so more effectively than the basic 4-point roll bars we have used in my last 3 personal race car builds. I own a shop that builds roll cages and haven't had one in my own cars in 6 years... that's crazy.

Corvette roll cages are tricky. All Corvette chassis generations (C1-C7) have a strong metal frame (steel frames through the C5, with aluminum frames for C6 Z06 and all C7s) with a composite body attached to it. Adding a roll cage to these cars has some extra challenges, since you need to cut away fiberglass to access the metal frames, but its nothing we haven't done before.

As I spoke about above, TIME is not on our side for this first NASA event, so we had to cut back on the roll cage plans for the maiden voyage. We could have bought a second-hand 4-point roll bar but it would never fit as tight to the roof structure in this gutted car (they are usually made for full interior cars).

Frame differences on the 1984-1991 (left) and 1992-1996 (right) C4 Corvettes

Quick sidebar: the C4 Corvette had major changes to the suspension (1989) and even to the frame (1992), along with major changes to the drivetrain (1989 for ZF and 1992 for LT1), front crossmember, and transmission tunnel over the 13 year long model run. The two "body shop spec" images above show the changes to the frame at the 1992 model year, and we've noticed a lot of other differences to the interior fiberglass structure.

Last year we caged and safety prepped a 1987 Corvette convertible (shown above) and after looking at pictures of both that and our 1992, it had a lot of structural differences at the tunnel, firewall, and rear bulkhead (behind the front seats), not to mention the dash, body, and other obvious differences. The frame was also different in some key areas. We are using the NASA CCR for cage design specifications on our car, but the black 87 used a mix of NASA, WRL, Lemons and ChumpCar series cage rules.

A Brief History of Iron and Steel

OK, this is a big tangent. It might not be boring to a racer - unless you are a metallurgical engineer. Modern race car roll cages are made from steel tubing (aluminum is not allowed) and picking the right alloy and type of tubing for the job involves both a rule book (General Competition Rules or GCR/CCR) and some engineering knowledge. There are generally TWO accepted types of tubing allowed for roll cages in SCCA and NASA: 4130 Alloy steel and 1018/1020 Low Carbon (aka: Mild steel) Steel DOM tubing.

Working as a Mechanical Engineer at a foundry in my first job out of college exposed me to a lot of practical metallurgical design and lots of different steel alloys. I also took a welding class at college, where we talked a lot about steel and iron and the changes welding can do to metal's molecular structures. That's where I learned that steel is the best metal on planet earth, and in many ways unique among all metals.

Iron is is, by mass, the most common element on Earth, forming much of Earth's outer and inner core (same scenario in almost any rocky planet). It is also the fourth most common element in the Earth's crust, which means it is relatively easy for humans to get at and mine. The production of iron by humans began sometime around 2000 BC and was so significant it began what is now called the Iron Age - when iron replaced bronze in implements and weapons. This shift occurred because iron, when alloyed with a bit of carbon, is harder, more durable, and holds a sharper edge than bronze. For nearly four thousand years, until replaced by steel after ~1870, iron formed the material basis of human civilization in Europe, Asia, and Africa. Iron has shaped human history for the past four thousand years, and it's use accelerated technological growth.

Natural "iron ore" has a lot of oxygen in it, so it is smelted at high temperatures to extract a more pure mass of iron. Carbon naturally gets mixed in at these high temperatures (along with 2-3 other elements) which means cast iron has a relatively high proportion of carbon (3-4.5%). This makes cast iron hard and brittle; it is liable to crack or shatter under a heavy blow, and it cannot be forged.

Blacksmiths learned to work iron - after heating it in a furnace at high temps they removed a pasty mass and hammered it on an anvil to drive out the cinders and slag and to compact the metallic particles. This Wrought iron (“wrought” means “worked” or hammered) contained generally from 0.02 to 0.08% percent of carbon (absorbed from the charcoal), just enough to make the metal both tough and malleable. Wrought iron was the most commonly produced metal through most of the Iron Age.

Steel alloys have a little bit of carbon in them (0.2 to 1.5%), enough to make them harder than wrought iron, but not so much as to make it as brittle as cast iron.

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Its hardness combined with its flexibility (from some other alloying elements) and high tensile strength make steel far more useful than either type of iron: it is more durable and holds a sharp edge better than the softer wrought iron, but it resists shock and tension better than the more brittle cast iron. After about 1856 (the invention of the Bessemer converter) and into the 1870's (Andrew Carnegie's grasp of the vital importance of chemistry in steel making) steel alloys became cheap to manufacture and exploded in use, replacing wrought iron rails in railroad tracks and other uses.

Some of the sources I used, other than past knowledge: This and this and that , and more .

Modern Roll Cage Steel Choices - 4130 vs 1020/1080 Alloys

There are two basic steel alloys used in roll cage structures and we will start with the "stronger" and more expensive alloy allowed: 4130. AISI 4130 alloy steel is about 97% Iron and has 6 other alloying agents that make up the last 3%. Chromium (0.80 – 1.10%) Molybdenum (0.15 – 0.25%) are the two key elements added that give this metal its higher tensile and yield strengths, and are the two most expensive elements in the alloy as well - hence the nickname "Chromoly Steel". These alloys are harder to weld properly (generally they are only TIG welded) when compared to Low Carbon/Mild steels. The yield strength of 4130 is 66,700 psi (67 KSI) and when this metal is used, a little LESS of this alloy is needed to achieve the same total assembly strength as Mild steel. It has a good strength to weight ratio, but the same density as all steels (all steel alloys and iron have nearly the exact same density, .284 lbs/cubic inch, due to the fact that all steel alloys are still almost entirely made of iron). In the past, roll cage rules allowed for thinner 4130 tubing to be used relative to Mild Steel, but that is no longer the case for most road racing bodies.

I used to use a lot of "A36" mild steel 15-20 years ago when I designed oilfield equipment, which had a minimum yield strength of 36KSI, which is relatively soft and very cheap. The modern 10XX series steels have gotten better and a lot stronger - closer in strength to 41XX Chromoly steels, but without the negatives. AISI 1018 and 1020 "Low Carbon" or "Mild" Steel alloys (also known simply as Carbon Steel) are lower cost and slightly weaker than 4130, but these 10XX series alloys have excellent weldability and offer a good balance of toughness, strength and ductility. Once cold worked (via the DOM or CDS process) these Mild steels become even stronger and stiffer.

1018 steel (0.14 - 0.20% Carbon) has a yield of 54KSI and 1020 steel (0.18-0.23% Carbon) has a 51 KSI yield - which isn't that far off of 4130 (67 KSI). Ultimately 4130 is about 20% stronger than Mild steel. But 1018 tubing that is DOM cold worked gets stronger, and is rated at 70KSI, and 1020 DOM tubing is rated is 65 KSI. Cold working 4130 tubing via the DOM process turns it up to 90 KSI yield... roughly 22% stronger.

The key benefit to racers building roll cages out of Mild steel over Chromoly is that 10XX alloy steel is much more forgiving with respect to weld embrittlement and tends to "crash better" than the harder "alloy" steels. When you weld the 41XX series alloys the molecular structure of the alloy changes near the heat affected zone, especially if you put too much heat into the weld (and some welders like to "weld hot", which can really make the weld area change), so 4130 cages are almost exclusively welded with the trickier TIG welding process (a Tungsten tipped torch with a shielding gas and a separate metal rod, with a variable control on the welding arc).

Mild steel isn't nearly as susceptible to this issue and can be TIG or MIG welded and generally does not lose much strength at the welded joints. 10-20 years ago 4130 was all the rage for roll cages but lately 1018 or 1020 Mild steel is the norm, as long as they are DOM. To me nothing beats a properly designed, TIG welded, Mild Steel DOM tubing roll cage. This has the best combination of variables and the least number of compromises.

DOM vs ERW Tubing?

ERW or "Electro Resistance Welded" tubing is how steel tubing and pipe is made (at least initially) - where a continuous, flat roll hot rolled steel is bent around round (or square or rectangular) dies and welded at a seam (see image above). That's how lower cost pipe and tubing is left - with this visible welded seam on the outside and often a physical "ridge" on the inside of the tube (see below). This problem is - seam ultimately becomes the weakest point in this type of tubing. And the hot roll plate material isn't ever as strong as cold worked steel.

A visible seam and often a raised ridge is the result of the welding process from ERW tubing. All tubing starts as ERW...

The DOM process (Drawn Over Mandrel) takes ERW tubing and "cold works" it by drawing over a round mandrel and through round dies, inside and out. This makes the now DOM tubing "seamless" (its really hard to find the seam with your eyeball) and work hardens the steel structure - adding strength and removing the stress riser at the seam. ERW tubing was previously allowed in roll cages (up until just a few years ago) and the various CCR/GCR rules sometimes still reference ERW for "grandfathered" cages built before it was outlawed, but nowadays all roll cages are spec'd as seamless tubing - either 1018/1020 Mild Steel (DOM or CDS) or 4130 Alloy steel (DOM or CDS). There's another cold working seamless tubing process nowadays called CDS (Cold Drawn Seamless ), but I can't seem to find any CDS tubing in common roll cage sizes - yet. The CDS specification seems to be more common in Europe. It could be the exact same process as DOM, but some U.S. tubing companies specify them separately, so I don't know.

The stiffness difference between ERW and DOM is shown in this video, with the same diameter and wall thickness tubes of both types in a side-by-side bending test. The lower strength of ERW + the stress riser of the seam are why it isn't specified in roll cages any longer, but it was a pretty recent deletion from roll cage specifications.

The FIA has updated their specified tubing to 350 N/mm2 (50.76 KSI) tensile strength (see page 46, rule 8.3 of Appendix K here ), and material is simply listed as "Cold drawn seamless carbon steel". They used to only spec 4130 alloy tubing (or the European equivalent) but even the French have seen the benefits of using Mild Steel DOM/CDS tubing. As we have seen with changes to rules specs, ERW is no longer allowed and the advantages in welding Mild Steel outweigh the weight savings or 20% strength benefits of 4130 Chromoly.

Picking the Tubing Material, Tubing Sizes and Cage Design Layout

OK, that got a bit long, but it was hopefully worthwhile tech. Now that we know why we use steel, know more about the alloys, understand the benefits of the cold working and seamless processes that are required in the steel tubing specified, and why more cages are using mild steel DOM - let's pick the cage tubing size for this build and show some Corvette cage pictures already!

Many of the cars we work on at Vorshlag lately, that are built around NASA specs, weigh over 3000 pounds so we're often using 1.75" diameter x .120" wall thickness DOM Mild steel tubing. And since the 1992-96 C4 Corvette is listed as a base class of TTC and a Minimum Competition Weight of 3203 pounds, I assumed that we had to use this tubing size. This is nearly the heaviest cage tubing in all of the NASA CCR , but lower weight cars can use thinner tubing diameters and wall thicknesses, as shown below (copied from the 2015 NASA CCR).

NASA 15.6.18 - Roll Cage Tubing Sizes

For the purposes of determining roll bar tubing sizes, vehicle weight is as raced, but without fuel and driver. Minimum tubing size for the roll cage is:

Up to 1500 lbs:

• 1.375” x 0.095” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM
• 1.500” x 0.080” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM

1501 - 2500 lbs:

• 1.500” x 0.095” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM

2501 - 3000 lbs:

• 1.500” x 0.120” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM
• 1.750” x 0.095” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM

3001 - 4000 lbs:

• 1.750” x .120” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM

Over 4000 lbs:

• 2.000” x 0.120” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical) or DOM

Since we do not need to include the weight of the driver (200 pounds) or fuel (20 gal x 6 pounds/gallon = 120 pounds), that means our goal weight of 3203 really translates to a caged race car weight of about 2900 pounds. So we can use the lighter 1.75" x .095" wall DOM Mild Steel tubing. I like this for two reasons. First, we have a bunch of this tubing already in stock at the shop. And two, we typically bend 1.75" tubing, so our tubing bender has this set of dies already installed. Right now we're building two cages at once, both with 1.75" diameter tubing (one is .095 and the other is .120" wall), so we won't have to keep switching the dies. This thinner wall tubing is also easier to bend.

We use a JD2 Model 32 manual tubing bender and dies

The weight is not insignificant: 1.75" x 120" wall DOM weighs 2.089 pounds/foot of tube length. The 1.75" x .095" wall DOM weighs 1.679 pounds/foot (19.6% lighter and about the same amount cheaper). The other choice for this weight is 1.5" x .120" wall DOM, which weighs more at 1.769 pounds/foot. Sure, we could have stepped up to a larger tubing size, but those CCR minimums are there for a good reason... mega-sized tube in a smaller/lighter car makes for less room to the driver and less energy absorption in a crash, so we're going with the recommended tubing range for a 2900 pound car, then picking the larger tubing diameter of the two options given there, which is slightly lighter.

Cage Layout and Design

There are three cage design options we can choose form the NASA CCR, shown in 15.6.8, -.9 and -.10. We're going with the "Forward Hoops" version from 15.6.8, shown above. This is the most common of the 3 methods (another is the "Halo style") and makes for the most room for the driver's head in a car like this. So about halfway through the day on Friday the 2nd, our fabricator Olof stared work on the cage install. He will build a majority of this cage while Ryan finishes a cage on another car at the same time.

Before you can start bending any tubes you have to clear out the interior. This car was already gutted, which saved us 15-20 hours of labor. That work is never included in the "cage" price, which some people don't always understand. If you want to save some money, bring in a NAKED car with zero interior bits, like this. I came in early that Friday and removed the driver's seat and targa top, then the guys pulled the rear hatch glass off.

The driver's seat normally weighs more than this, but it was alreay partially gutted by Matteucci and only tipped the scales at 34 pounds - I've weighed a lot of modern power front seats in the 60-75 pound range. The targa top weighed less than I had thought at 22 pounds. This is the plexiglass "See through" version, but I'm looking for a fiberglass version (both were offered from the factory) which we could paint white to match the car, but they sell for $$$ used. The weight is mostly in the metal frame structure, so the Plexiglass vs Fiberglass is probably a wash - except the fiberglass OEM version is likely stiffer. We might replace the Plexiglass with a custom Carbon Fiber skin (stiffer than Fiberglass). Is it legal? Well since we can run with the targa top removed (wouldn't that make its construction insignificant?) and as I read TT rule 8.3.B, we can lighten the "roof, hood, body panels and doors" as long as they "maintain their BTM (Base Trim Model) size and shape". The "no points" listing for I.h.20 says the same thing, with more details with respect to carbon/fiberglass doors being legal as long as the BTM body lines, hinges and handles are still operational. And an in-house built Carbon Fiber roof would be, you know, cool...

The rear glass was much heavier at 46 pounds. That bit will likely never go back onto this car, as we have a formed, 3/16", trimmed Plexiglass rear hatch replacement inbound that should save 30+ pounds. I will show that in my next post, if it gets here before the NASA race Jan 17th. This is legal per the "No Points Modifications" rule I.b.8, as long as it has the factory BTM shape and no uncovered holes.

Once the interior was cleared out enough to start Olof began cutting bits of fiberglass out of the way. See why I had the pictures of the C4 frame structures up above? That was to help us find where the frame is - which isn't obvious in some areas as there are big gaps between the shape of the interior fiberglass structure and the metal underneath.

If you ever get a roll cage quote on a Corvette, now you know why it costs more than a traditional steel unibody car - because you have to cut access holes to get to the frame. And they need to be fairly big holes, to give the fabricator access to weld a reinforcement plate to the frame. Then you have to close up the holes in the fiberglass later... all of that is extra work.

Once you have access to the frame structure it has to be cleaned of all paint (we use a pneumatic wire brush tool called a "Crud Buster" along with a flap disc on an electric angle grinder). Then the plates are drawn in cardboard and transferred to steel, in this case 1/8" thick hot rolled plate (minimum thickness is .080" for these plates, but we tend to use .125", since it is stronger and easier to weld).

Olof cut the plates and tack welded them to the frame at the main hoop, which is in an unusual spot. Normally the main hoop mounts to the floor behind the driver's seat - often 6-8+ inches behind the back of the seat. But in a Corvette, for tall-ish folks, the back of the seat ends up right at the rear bulkhead, so the main hoop has to go up on the rear deck area. The frame extends up here and we've checked with NASA inspectors on Corvette cage hoop placements and have also built cages in Corvettes like this. Miata cage main hoops are done the same way - just the nature of these 2 seat cars and their compact interiors.

On Monday the 5th, Olof designed and bent the main hoop, with help from our head fabricator Ryan. They got the hoop TIGHT up against the high strength steel roof structure, and placed it back the correct distance from my head. We had already done a number of seat mock-ups at this point and we knew where I needed to sit - with the seat almost touching the rear bulkhead. This put the main hoop where it is above.

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By this point we had switched our focus from the larger Kirkey aluminum seat we had in stock, to a PORNO RED! Cobra Suzuka Kevlar FIA seat we "horse traded" with a friend for. My buddy Jason McCall had ordered this seat from us last year for his 1989 Corvette but it wasn't fitting with the electric seat adjuster he wanted to use (for better fit with his shorter co-driver - his wife). It is brand new and still good through 2019 on the FIA certification.

This seat happened at the 11th hour - the day Olof needed to start on the seat mounting and to lay out the harness bar. It turns out our aluminum seat fits better in his full interior C4 and his composite Cobra seat fits better in my gutted C4 with no slider. So we made a seat swaperoo!

Once more access holes were cut in the rear fiberglass (shown below left) the rear downbars could be cut, notched and built. These will land on 1/8" thick pads on top of the frame, as shown. Two thickness of pad, actually...

One of the compromises made from our reduced timeline was that the cage became a weld-in 4-point roll bar, and then when we looked at the next step, it became a bolt-in roll bar. Now before you hurl insults, you have to realize that this is going to be a VERY beefy design that can still become a proper weld-in roll cage shortly after the first race. Weld-on "nut plates" (see above right) were created and access holes for the nuts were cut in the frame. This is because the frame is fully boxed and we couldn't bolt into the frame otherwise. These plates have nuts welded to the back side and will be seam welded to the frame, then a matching "footer" plate from the 4 main tubes will land onto these and bolt in place.

All this bolt-in nonsense was done for future access. After our first TT event we have a month off before the SCCA Club Trials event at TWS. During this break we can take the time to turn the 4-point roll bar into a fully welded in 6-point roll cage. The front cage section and door bars take the most time to fit, and we ran out of time. But to do the final welding on the door bars and A-pillar tubes, the cage has to be rotated forward and down, and this bolt-in rear layout will allow for this rear section to be moved for that access. Once the final welding is done up front the four "footers" of the roll bar portion will be welded to the frame plates, and the bolts can be removed. Make sense?

Yes, that's a little crazy, but our 2 week timeline was just too tight to fully cage the car AND do all of the other performance, safety and maintenance work needed. Next up in the roll bar design is the main harness bar (which the shoulder harness straps will wrap around), then the main hoop diagonal. This is a horizontal bar that is kicked back from the main hoop about 5 inches, to allow for the shoulder harness adjusters to loop around the bar.

The diagonal bar was cut and being tack welded in right before I made this post on Friday Jan 9th. One more tube is needed for the roll bar (a short tube connecting the harness bar and diagonal) and then it will come out for TIG welding. All of the pictures shown were just tack welds, which were done with the MIG. I'll show the rest of the roll bar and all of the other work happening next week in my follow-up "initial race prep" post. Gotta wrap it up!

Seat Mounting

Mounting a racing seat into a car is NEVER a fun job - installing a real racing seat is always a LOT more work than you might think. Ask any race car fabricator and they will tell you that this type of job sucks. We've installed a lot of racing seats over the years and it is never an easy "bolt-in". Any off-the-shelf seat bracket we've ever seen usually needs massive modification, and some of them raise the seat height by 2-5 inches. They only seem to work for little tiny short European children. Its a dirty little secret in motorsports - bolt-in seat brackets for fixed-back seats almost never fit.

And this only gets worse with drivers over 6 feet tall with racing helmets adding another 2-3" to their torso height. At 6'3", I'm not a good fit in many OEM seats much less with a racing helmet added. Here at Vorshlag there are 5 people that are 6'2" tall or taller, so we're all used to these seat mounting headaches. The Corvettes from C4-C7 are all pretty cramped inside as well, and we've had to really fight to make racing seats fit in these cars.

In the most difficult situations (cramped cabin + tall driver) it is not uncommon to spend 6-8 hours fabricating mounts for one seat. Adding in a slider makes this take even longer, but we were out of room here and just mounted the seats directly to the floor (my co-driver Matteucci is almost the same height, luckily).

Olof took most of a day to test fit the seat (with me sitting in it in a helmet), mock-up the angles and height, reinforce the floor, then modify the OMP side brackets (see image in this section) to get the seat bolted in where I had enough head room to the targa roof with a helmet on. It was tricky and he lowered the "lowest" mounting holes in the OMP brackets by about 5 inches. The original OMP seat mounting holes are crazy tall - doesn't matter what brand of brackets, this always happens.

I don't have good pictures of the seat mounting from underneath, with the car in the air, but we have beefed up all of the seat mounting points to the chassis. The rear studs were removed and an 1/8" thick doubler runs across the entire width under the steel floor pan section. The front studs were also reinforced. We are adding clip-in harnesses so eyelets with reinforcement plates will go in for lap belt anchors as well as a solid mount for the anti-sub belt under the seat. Will show all of this next time.

Tires Are Everything

Its time to talk about the single most important aspect of this TTC build - the wheels and the TIRES.

Tires are the most important aspect of a road race car. Let me repeat that for emphasis: Tires Are The Most Important Thing In Racing. The four tire contact patches are the only things connecting your car to the race track. Through these four little patches all of your forward accelerations, braking and cornering loads are generated. All of the work we do on the suspension is just to make sure the tires are happy - to make them stay flat, to always keep them in contact with the road, and to make sure loads are distributed as evenly to all 4 patches as possible.

So with this car being based in TTC class with a 7 point penalty, that leaves us with only 12 points to work with (19 class points - 7 penalty). And while that gives us some options for lots of different mods (upgrading power, brakes, suspension, lightening the weight, aero and tires), we're going to burn almost all of our points on the tires. This is a very critical decision, so let me explain what we're doing. This decision was made after hours of internal debate, hundreds of permutations of width + compound (+ other non-tire mods), but mostly comes from years of racing experience and knowledge: Knowing that the tires are almost all that matter.

TIRE WIDTH - As I pointed out in a previous post, everything you modify in the TT letter classes is either listed as a No Points Modification (which we are using every one we can!) or is assigned a number of points. It is all clearly stated in the TT rules. Tire width changes are "expensive", and the points in sizes increases above the "base class size" (TTC = 255mm) are shown below.

• Equal to or greater than: 10mm +1, 20mm +4, 30mm +7, 40mm +10, 50mm +13, 60mm +16, 70mm +19, 80mm +22, 90mm +25, 100mm +28, 110mm +31, 120mm +34, etc.
• Equal to or less than: -10mm -1, -20mm -4, -30mm -7, -40mm -10,

Big Wheels Keep On Turning!

As you can see you can get points BACK by going to a SMALLER tire as well. There is no other way in TT-Letter classes to gain points back, so this a big deal - and something we are going to do. Many will be surprised by this, as I've preached "BIGGER IS BETTER" for so many years. And while that is still true, we just don't have the points to go bigger, and feel that burning the points ALL on the compound makes more sense. Here's a comment from a corner-carvers reader and my reply:

Will the rules let you put 335's on? 17x12" rims are a bolt on affair.

Yes, it would is technically "legal" to run 335mm tires on a C4, but unfortunately the points just aren't there to do this and stay in TTC class. We're going to be running much narrower tires than that, but with what we feel is the right compound.

These pictures are of Jason McCall's 1989 Corvette that is prepped for SCCA BSP class (and was the National Championship winning car in 2005). It runs 17x11" CCW wheels in front and 17x12" wheels out back with Hoosier A6s in 315mm up front and 335mm out back. The fit is pretty tight - it has custom flared front "fenders" (the hood) and has the little 1996 Grand Sport "export" flares out back to make these fit - and we can legally add flares for zero points.

I've driven and ridden in this car and it is a GRIP MACHINE, just a big go-kart. Very fun, and the wide, sticky autocross compound tires he runs are why its so fast. And while I'd love to do this on our C4, the points for the compound (Hoosier A6 = +17 points and A7 = +22 points!) plus the increase in tire width (255->335 = +80mm = +22 points) would cost a whopping +44 points for just this tire upgrade. Using all of the points we have in TTC (19 - 7 = 12) and then even moving up to TTB (+20 more) we're still short by 12 points for a 335mm A7, so that tire choice would be a move straight to TT3. This is why we cannot use the tires we'd LIKE to use (I'd slap 335mm Hoosier A7 tires on this in an instant if the points allowed it!) but the compromise we have chosen will still work well enough - we suspect. Remember: Everything in racing is a compromise... and everything depends on everything else.

Many of you that have experience with the C4 Corvette know that most of the later C4s came with a 275/40/17 tire on 17x9.5" wheels at all four corners, as did our 1992 Base Trim Model Corvette. But the TTC class "base tire" is 255mm, no matter what the OEMs put on the car. Wheel width is unrestricted, other than a track width change limit of +4 inches. Beyond that you take points. Our car has 285/40/17 old and crusty street tires on it right now, which would cost us (+30mm over 255) +7 points to use, but they are a joke. So hard they can spin freely through the first 3 gears. I won't be caught dead on a road course with old street tires, not even brand new 120-200 treadwear street tires (which are worth +2 points), unless the rules require that for everyone.

After racing our TT3 car in various "street tire" events/series last year, and at some tracks we also ran with R-compound Hoosier A6s in other series, I know the true lap time value of sticky R-compound tires. Going from a 335mm BFGoodrich Rival to a 345mm Hoosier A6 is worth a MASSIVE amount of time. On a typical 2 minute road course that difference is 5-7+ seconds per lap with the Hoosier over a 200 treadwear tire, and the Hoosier is MUCH easier to drive. So we're gonna stick with what we KNOW works and that has a great NASA TT contingency program: Hoosier.

TIRE COMPOUND - The compound of the tire is as important than width in Time Trial. Maybe even more important. Why? Because every TT lap is essentially run at a Qualifying lap pace, where you need to be pushing 10/10ths. To win you just need to set ONE fast lap per day (each day is a new competition), and waiting around for 3-4 laps for your "tires to warm up" will only get you mired up in traffic, as the front of the field catches the back end. There are a LOT of tire compounds listed and points assigned for each. The only "free" tire compound in TT-letter are those over 200 UTQG treadwear numbers. The tire models are grouped together with compound and performance parity, and the points given look to be pretty fair. There were massive adjustments made to these points for 2015, which was long overdue.

• DOT-approved R-compound tires: BFG R1S, Goodyear Eagle RS AC (autocross), Hankook Z214 (C90 & C91 compound only), Hoosier A7, Hoosier Wet DOT (if used in dry conditions—see section 5.6) +22
• DOT-approved R-compound tires: Hoosier A6 +17
• DOT-approved R-compound tires and those with a UTQG treadwear rating of 40 or less not listed otherwise in these rules: BFG R1, Goodyear Eagle RS, Hankook Z214 (C71, C70, C51, C50), Hoosier R6 & R7 & SM7, Kumho V710 (note: Continental Tire Sportscar Challenge EC-Dry tires OK (225, 245, 275) +10
• DOT-approved R-compound tires: Toyo Proxes RR, Hankook TD +7
• DOT-approved R-compound tires and those with a UTQG treadwear rating of 50 to 130: Maxxis RC-1 (ex. Kumho V700, Michelin Pilot Sport Cup, Nitto NT01, Pirelli PZero Corsa, Toyo R888, Toyo RA-1, Yokahama A048, etc.) +6
• (non-R-compound) tires with a UTQG treadwear rating of 120-200 (examples: BFG g-Force Rival, Bridgestone Potenza RE070, Dunlop Direzza Sport Z1 Star Spec, Hankook R-S3, Kumho Ecsta XS, Toyo R1R, Yokohama Advan A046 & Neova AD08,) +2
• Non-DOT-approved racing slicks +30

That is a dizzying array of compound choices and, when combined with the size choices, it makes for a lot of possibilities. But we've run the numbers using these compounds + various widths and have settled upon: 245/40/17 Hoosier R7. Not the softest tire but damned close. Not the widest tire but "wide enough" (and it gives us a point back). The tire choices are still very limited in the brand new Hoosier A7/R7 compounds, but this seems to fit the bill. The spec's on this particular 245mm tire look pretty dang good, and I'm hearing good things about the R7 compound in tests. Our first event will teach us a lot... either we guessed right or made a big mistake!

These wheels are stupid light! We will weigh the wheels alone once the old 275 Hoosiers that came on them are dismounted

WHEELS - We will run these Hoosiers initially on some 17x9.5" SSR wheels, which are both light and strong. Very light, in fact... around 15 pounds. Getting a set of these Corvette sized SSRs is like finding a wild unicorn - very rare and no longer made. SSR went out of business after the 2008 recession but it seems that they have reformed and are back - but not making a lot of the "big" sizes that fit Corvettes any longer. This set came from our shop manager Brad's former Super Stock 1994 Corvette, and he has two identical sets in perfect shape. I have dibs one set but the other is available. The Hoosier A6s on these wheels are DOT stamped from 2008! These wheels are perfect and have been sitting in his attic for almost 7 years.

What's Next

I could go on. And on. But I have probably bored you enough! Our crew is still busy at work finishing the prep on the Corvette for the first race and I'll try to do a quick update next week, right before we head down to MSR Houston Jan 16th. There's still a lot to do and not much time left...

Cheers,

Terry Fair at Vorshlag Motorsports

For the crap guys are giving you for "home building" this I dont care. The well thought out layout and great information entertains me to no end. I will verily miss the 2013 GT build thread.

Fantastic detail, fantastic read

Good post Terry. I should be at MSRH and will come by to say hi. We've met a couple of times. I was the noob in the black CTS-V wagon at TWS in the rain at the end of the year.
This is a cool car.

Mad_Ratel wrote: For the crap guys are giving you for "home building" this I dont care. The well thought out layout and great information entertains me to no end. I will verily miss the 2013 GT build thread.

Well, the Corvette isn't a home build. It's being built at Vorshlag by our fabricators. The V8-E30 was a home built car. It was built out of Terry's house and at the time he had one mechanic that could swap parts, but not fabricate, working for him. All the work on that car was done by friends that got together every evening after work. Me, I came by and laughed at them. But the car ended up doing well.

Yea, this Corvette is definitely not being "garage built" but we are tracking every dollar, and heavily restricted on mods due to the class we are running. The GRM $2011 E30 was my last full "garage build", back in 2009-2011.

One unusual aspect of this project is that -I- am getting my ass out into the shop to help more on this build, since it is going to be my car.

I came in this weekend and worked a few hours upgrading the front brakes from the 12.0" 1992 base brakes (shown above), cleaned 24 years of gunk from the front suspension...

Then swapped on the 1996 base trim model Corvette 13.0" rotors, rebuilt PBR calipers, and Carbotech brakes.

I will cover more of the brake upgrades, and how we got these into a TTC build for zero points, in my next update. Got the SSR 17x9.5" wheels cleaned up and they look good, too.

More soon,

Terry Fair @ Vorshlag

Project Update for January 16th, 2015: The first stage of "initial race prep" is completed and I'm going to try to write a QUICK update before we load up and I head down to Houston (in the next few minutes!) for the first NASA Texas event of 2015. We had a lot of parts delays but the crew at Vorshlag got everything on the "MUST HAVE" list completed. They only worked on this car over an 8 day period - due to other cars on the schedule. Big thanks go out to Olof, Ryan, Brad and Jon for all their hard work and long hours over the past week and a half. Thanks also to Jason and Tim for helping pick the mods and source the parts we used. Now all I have to do is drive the thing well... but I have a good back-up driver in Brian Matteucci, thankfully.

Brake Upgrade

The last week was a blur, as we had a lot going on in the shop with other customer cars, the phone rings off the hook in January (everyone waits until now to order parts for the new race season), and we're still gearing up for our new CNC machines - which has been a royal PITA. I had a birthday this week, and tons of other crap going on, and I usually work seven days a week playing catch-up on Vorshlag stuff on the weekends. But last weekend I stole a day away to swap on the front brakes.

Left: The 12" front brakes are adequate but can be upgraded to 13" rotors "for free" (no points). Right: The two rotors in question

So the 1992-1995 "Base Trim Model" Corvettes all came with these wimpy looking front brakes, shown above. These include the 12.0" diameter x .810" thick vented rotor and PBR twin piston aluminum caliper, which I detailed a bit in my Dec 29th build thread post (post #5 for most of the forums). And I hinted that we would be able to upgrade from the 12" to the 13" rotor set-up for "no points". Normally this is a +2 upgrade, and we only have 3 total points left to play with. I'm saving those for later so we pulled the trigger on the correct rotors, calipers and caliper brackets back on Dec 23rd.

The measured weights for the two front rotor sizes were pretty close to the spec sheets from Centric. Since nobody seems to want to work the last 2 weeks of a year in the USA, we didn't see these parts until late last week (around Jan 9th), and I started installing them on Saturday the 10th. The right front set-up went on fine, but I got bogged down cleaning the front suspension and wheel well...

It was worth it seeing the beautiful, forged aluminum uprights and control arms after 45 minutes of brake cleaner and WD-40 plus some elbow grease got 24 years of gunk and grease build-up off of the metal. Be careful with brake parts cleaner as it is pretty aggressive, but it cuts through the thick caked on grease well. Once I started to see metal underneath I switched to WD-40, and used WD-40 only on all of the plastics and rubber seals. Decades of road dirt wipes off after a little soak with WD.

Cleaning the gunk showed me a split ball joint boot, which we will replace in another round up upgrades later (along with all of the original, crusty rubber suspension bushings - which can be replaced with any non-metal bushings). The old bits came off easily enough and the new 13" rotor and longer caliper bracket went on. And yes, we gained a solid 7 pounds in the rotor upgrade, but its "good" weight. This is cast iron that can both soak up brake heat and more rotor area and vanes to help radiate brake heat. This car will be 3203 pounds with driver and ballast and that's a lot of mass to slow down for thin little 12" brakes at both ends.

The 2-piston sliding PBR calipers (3.56 pounds) are familiar to me, as I've used them on SN95 Mustang Cobras and 3rd gen 1LE/B4C Camaros in the past, as well as on my 94 Corvette - which had the Z07 package and these larger "J55" option 13" front brakes. The J55 calipers are wider, and the J55 caliper bracket (2.56 pounds) is longer, but neither is much heavier than the "base" brake parts.

How are we getting to use the "bigger" J55 brakes from the Z51/Z07/ZR1/GrandSport models without points? Well the trick is this: all 1996 Corvettes models came with the larger J55 brakes, including the base trim model. And the listing for the car we have (1992 Corvette) is listed as 1992-96 Corvette (non ZR1, non-LT4). So we're updating to the base trim level brakes for the 1996 model car, since the 1992-96 cars are listed on the same line (again, not the 1996 LT4 or Grand Sport). We can also play around with swaybars and springs from the 1996 base trim model cars, which we might do later. Here's the rule that makes it all happen...

Rule 8.5, page 41 of the TT ruleset for 2015:

Updating of parts between different model years of the same vehicle model is legal provided that the competing vehicle is both in the same model group listing (same line) in the Table in 8.2.2, and in the same generation of that vehicle model, and that the entire assembly is replaced. Backdating of parts between different model years of the same vehicle model is legal provided that the competing vehicle is both in the same generation and is in the same or higher base class. No interchange of parts between assemblies is permitted in order to create a new assembly.

Just like in SCCA Solo, this "update/backdate" rule can be exploited to your advantage. It takes a lot of research and sometimes rummaging in junkyards, but it is there as a tool for dedicated racers to use. It helps to have factory manuals as well, which we do (thanks to Matteucci).

Again, this is a simple bolt-on upgrade and we have to use OEM (or OEM equivalent) parts to make it legal. No 2-piece rotors, no aftermarket calipers, this is all real deal GM bits. The brackets are from GM and the calipers are rebuilt GM calipers. So getting the right front corner swapped to the J55 bits took less than half an hour. I added blue loctite to the caliper bracket bolts, torqued it all to spec, re-used the old brake hoses (we will make stainless lines when we have time) with new crush washers, installed new caliper retaining pin and E-clip, easy.

Then a friend stopped by the shop mid-day Saturday and convinced me to go see the Interview at the Alamo Draft House. The movie was hilarious and I'm glad I went, but it put me behind on the right front brakes. No worries, I'll do it Sunday.... nope! Amy made me go write the eBay ad for our TT3 prepped 2011 Mustang, which I did then started writing the massive OUSCI 2014 write-up, which I finished today and promptly deleted (it was too harsh).

So on Monday I came in and the guys were working on other items on the Corvette, so I got to work on the left front brake upgrade. As soon as I tried to put the left front caliper on, DOH! It didn't fit.

The box had the correct J55 caliper bracket (which moves the caliper out for the 1" larger diameter) but the wrong caliper casting. It was too narrow by almost .300" and would never fit over the thicker rotor (.300" thicker). Crap. We had ordered the right parts, and the part number on the box from Centric was correct, it just had the wrong damned part in it. Oh well, stuff happens. We took these pictures, sent them to Centric, let them kno how urgently we needed the right part, and hoped for the best.

Left: original Delco/Bilstein dampers. Right: New Bilstein OEM replacements went on

Luckily they got the right caliper to us just in the nick of time (Wednesday the 14th!). The OEM replacement shocks also arrived at the same time (also ordered in December and also very very late) and Olof and Brad got all of that installed when I was out running errands that day. We replaced factory base trim model "Delco Bilstein" dampers with the OEM replacement Bilsteins that were listed in our Bilstein dealer catalog. The two original rears were blown and the new bits matched up perfectly. These are non-adjustable and are considered replacement OEM dampers available, so they are a "zero point" install.

We re-used the Carbotech brake pads Matteucci had purchased for the OEM brakes, which were XP12 front and XP8 rear. A little soft for my tastes but they were brand new so we will use them for this first event. We pushed some Motul RBF600 through the lines and it felt good. Too many other fires to put out to get to brake cooling this time around so we'll keep an eye on the fluid and Alcon temp strips at this first event.

Tires and Wheels Installed

The Hoosiers arrived this week Olof dismounted the 7 year old crusty 275/40/17 A6 Hoosiers that were on Brad's 17x9.5" SSR wheels. Then he mounted the 245/40/17 Hoosier R7 tires and balanced them. They did all that while I was at lunch one day and I didn't get to weigh the wheels without any tires, so I'll have to do that next time, but I can do simple math. Just weighed an old 275 Hoosier that was removed (22.40 pounds) and the weight of the wheels+old tires (38.76 pounds) that puts the 17x9.5" ET55 SSR wheels at about 16.4 pounds each. Not too shabby.

The SSR wheels were a bit dirty so I cleaned 7 year old brake dust off of the inside barrel and spokes with more WD-40 and some elbow grease. The 245 R7 looks so tiny to me, after a season of using 345 A6 Hoosiers, but it doesn't look bad on the car.

We will see if burning 10 of our 13 class "mod points" on tire compound was worth it this weekend. This is an experiment that could pay off big or fail miserably.

Roll Bar, Harness, Seat and Fire Bottle Installed

With only 8 days of shop time we were not able to build a full roll cage (that will be a 3 week job by itself) but Olof did manage to get the roll bar built, reinforced, and mounted.

A big time suck on this job was making the aluminum cover plates. These are necessary on a fiberglass bodied car to cover the access holes in the body to the steel frame.

Again, on a traditional steel bodied/unibody chassis car this step is not necessary at all. But its a Corvette, and has to be a pain int he ass. Olof used card stock to make templates (below) that cover the access holes, then transferred this into .065" thick 3003 aluminum sheet.

The sheet was cut, bent and welded at the joints to make a box-like shape that fit the funky fiberglass tub shape and covered the openings with about a 1/2" overlap. Then a few holes were cut to add small stainless steel button head bolts and riv-nuts were added to the fiberglass (these are special ones we use just for fiberglass, with a different grip length than normal sheet metal riv-nuts)

A silicone bead was added to the perimeters of the fiberglass and these four, somewhat elaborate aluminum covers were then set in place and bolted down. These will now keep water, dirt and debris from spraying up from the tires and getting into the passenger cabin. Olof did a superb job and they look great and fit tight around the roll bare tubes. These can be removed and the roll bar unbolted for when we go back and finish the roll cage. Similar plates will be needed up front at the additional 2 lower points of the 6-point cage design.

We knew we were going to be WAY too light for the class minimum (3203 pounds) and would need anywhere from 90-200 pounds of ballast. On Tuesday we were getting a little tight on time so I asked Ryan to step away from a cage job he was working on and make the ballast weight bracket from some heavy 1x2" tubing. I was thinking of something basic but he made this beefy assembly with a slick, threaded top cap that fits over a 2" tube.

For ballast I purchased new 45 pound "olympic" style barbell plates with a 2" center hole. Typically cast steel weights like this cost around $1/pound, which is what I saw at a few places like WalMart. But after doing some shopping I found the best price at Academy sports, who had a wider assortment of better looking plates to choose from. These 45 pound plates were $31 each, or about $.68/pound. Sure, you can slum around on CraigsList and maybe find some mis-matched weights for around $.50/pound used, but its very hit or miss. Save yourself some hassles and go to Academy. If you want something more compact you can usually buy lead for $1/pound at plumbing supply stores, but just wear a mask when cutting or grinding on this stuff.

I didn't get any detail shots but the factory seat mounting studs (which are reinforced and rated for carrying up to 300 pound passengers) were used with some BIG bolts cut down on the lathe (and drilled/tapped to fit over the seat studs) go down from the top to secure the rack in place. You could pick the car up from this set-up and the 2" tube fits tight to the plates in sheer. At a minimum we will run 90 pounds of ballast here plus 120 pounds of fuel in the 20 gallon tank. Once we replace the 46 pound glass rear hatch with plexiglass we will add another 45 pound plate to the ballast box.

continued below

continued from above

The factory seat mounts are reinforced with extra steel from the factory, but we added more. 1/8" thick steel plate wraps around the stock stuff and was stitch welded to the floor as well as wrapped around up into the tunnel and frame on the sides, where it is bolted or welded for more support. The harness anchors for the lap and anti-sub belts are from G-force. These eyelets allow the clip-in ends from a Cobra/Schroth 6-point Profi-2 harness to attach. These are my favorite harnesses and made by Schorth in Germany to FIA specs. This set has 2" upper shoulder straps to better work with he NecksGen HANS device I will be wearing this weekend.

As usual, any "pretty" pictures you see here were shot by shop manager Brad with his Canon gear. The rest of the pics are from my "potato-cam" Galaxy S4 camera phone or my Nikon D90, which I can't seem to use worth a damn. The shoulder harnesses were wrapped around the harness bar tube with the proper wrap technique as specified in the diagram on page 42 of the NASA CCR.

Last but not least, a 2.5 pound fire extinguisher was added. This is a small "Halotron" (Halon replacement) hand held fire bottle that can be used to put out small electrical, oil or grass fires and doesn't leave a big mess of dry chemical or foam residue behind. We add these things to every track build possible, even when they have a full fire "system" with multiple nozzles. No need to blow a big bottle when all you have is a little grass fire under the car after pulling off track into dry grass. We used the Drake quick release mount here, which we have used a half dozen times. CNC aluminum, roll bar or floor mounting with the same kit, and one pin can be pulled for fast bottle removal but it stays tight and rattle free when racing. Good stuff.

Weight Check!

Now you've seen how crazy I am about dropping weight and weighing everything in this and other build threads. Weight is the enemy! Lowering weight helps all acceleration vectors, be it braking, forward acceleration or lateral acceleration (cornering). We do a LOT to lower the weight on any race car build, and this car has gone from about 3300 pounds stock (we never weighed this car with the interior but that's what my 1994 Corvette weighed) down to about 2720 pounds. This weight drop was from lighter wheels, no interior, no passenger seat no side or rear glass, and no HVAC bits. The air conditioning compressor has been removed as have the headlights. The lighter wheels and tires help, too.

Left: 2841 pounds with fuel but no driver or ballast. Right: 3200 with driver, fuel and ballast

We have added about 60 pounds in the roll bar and about 120 pounds of fuel (its nearly full) and the heavier J55 brakes and it was sitting at 2841 pounds. That's a solid 700 pounds lighter than our TT3 Mustang was without ballast or driver! Sadly we have to weigh 3203 pounds with driver (or else we have to burn points to run lighter), so ballast went back in in the above right picture to get us there. The plexiglass hatch should help remove about 30-35 pounds out of the 46 pound OEM glass, but it might not arrive in time, so we will save that 3rd 45 pound plate for then.

Classing Sheets, Dyno Test and Custom Tune

So we haven't built "letter" class car for NASA TT or PT before, but have helped a number of people class their cars. The base classing + mod points thing is nothing new to us. Just like TT# (numbered) classes, the TTx (letter) classes have an adjusted power to weight ratio. In TT3 the class has a 9:1 ratio but we were able to get ours to 8.8:1 with the adjustments. Likewise, TTC's base 12:0 pounds per horsepower limit has some adjustments as well, namely with a smaller tire...

Using the 245mm tire has had so many benefits and this is just one more - we get a 0.8 ratio bump for this small tire. That might not seem like a lot, but when you are at 3203 pounds it is nearly 20 extra horsepower allowed...

• 3203 pounds / 12 = 266.9 whp (267 rounded up, in favor of the driver)
• 3203/11.2 = 285.98 whp (286 rounded up, in favor of the driver)

Which is a good thing, as it was going to be hard to only make 267 whp even with a dead stock engine, manifolds, cats and muffler. We had the car over at True Street Motorsports yesterday and they were able to coax 284 whp and 331 wtq out of this 24 year old, bone stock iron block LT1, through the stock cats, manifolds and exhaust. Not too shabby. It even sounds better after the tune.

<a href="=http://vorshlag.smugmug.com/Projects/1992-Corvette-TTC-Build/46426384_Jb66DK#!i=3823956048&k=hrDsNbw&lb=1&s=A] Above: Video of the stock LT1 motor at idle and revving, after the dyno test.

We have our dyno plot and classing sheet attached below. As you can see we've started with TTC + 7 penalty points, which left us with 12 points to play with. We got one back for running 245mm tires (-10mm below base class tire) for 13 points total. We burned 10 on the Hoosier R7 and still have 3 points to play with. We will be very stingy how we spend those this season, so stay tuned to see what we invest these points in to make Danger Zone faster.

Left: The SAE corrected dyno plot making 284 whp. Right: TTC classing sheet with points

Last Minute Tweaks and Fluids

The Moroso oil pan for this motor is huge and the motor now holds 8.5 quarts of Mobil 1 synthetic oil (15W50 is my preferred weight for track cars), with a fresh Wix oil filter. Olof went over the car and filled out a NASA tech form but we still need to get a Logbook issued for the car at the event, so the plan is to leave Dallas early and make the 4.5 hour trek to south Houston on Firday and get there before dark. Then I can set-up the trailer, unhook, unload the C4, get the logbook tech and weighing, and make sure we have our ballast set correctly.

I couldn't leave the massive openings in the hood where the pop-up headlights used to be so I asked Olof to make some aluminum brackets to bolt to the inner hood structure and to the existing holes in the headlight covers. Those went on and now forms a fairly seamless clamshell hood surface. The front turn signal and corner light assemblies were also reinstalled to fill holes. We will go back and make flush mounted aluminum covers later, when we have the time.

Brad jumped into the Danger Zone this week as well and did a lot of wiring and some light fab work to the Corvette. He used to race a C4 himself and knows the car all too well. The wired AMB transponder from our TT3 car was moved to the C4 and Brad made some brackets for that, wired it up to a lighted switch (sometimes its handy to turn off the transponder - if we want to make another entry in the same car with the 2nd battery powered transponder we have). He also got the rear brake lights to work, after repairing some cut wires.

He made an aluminum panel to mount the switch in the center dash area as well as the 3-port "power panel" shown above. This was a cheap Amazon.com purchase which arrived in only a few days for $31 shipped. This panel has waterproof covers over a 12 Volt cigarette lighter port, a volt meter and a stack with dual 5 Volt USB ports (one a high amp and the other a low amp draw - see detail image above). Very slick little package that should prove handy when it powers my onboard vidcam and AiM SOLO timer. I will report back with how well this worked, or not.

The formed, lightweight, plexiglass rear hatch we ordered a week and a half ago arrived this morning so there's no time to fit it, so we reinstalled the OEM back glass. Order Desk Manager Jon wrapped the "ugly" mis-matched door with white vinyl. He also designed, cut and mounted graphics for our logos, "DANGER ZONE", Hoosier and Bilstein decals, and some class/number decals for all sides of the car.

Its time to load up so I didn't get the final pics... tune in next week for the post race update to see the final look, or look for it on Facebook with this hashtag #DANGERZONE.

What's Next?

The only thing on my RADAR right now, outside of cutting metal next week on our new CNC machines (tooling is FINALLY here!), is the race this weekend at MSR Houston. I will be paddocked with Costas, Matt White and other friends probably near Turns 16-17.

We are running MSR-H in the Clockwise direction this time (they alternate the direction for NASA events every other year), so I haven't run this track layout since 2013. The video above shows the lap record I managed in the TT3 car 2 years ago, on the skinny 315 tires. The lap record for TTC is currently a 1:50 but I think we might be able to manage a 1:46 if everything manages to stay together on the car...

http://www.nasa-tt.com/Texas_Track_Records/p2046_articleid/11

We have a pretty crazy class lined up: Our 92 Corvette, a 2003 Mini Cooper S (fully race prepped) and a 2005 Mazda RX8 (fully race prepped). Talk about an odd mix... and we will once again be the heaviest yet most powerful car in class, just like we were in TT3. I will post up more details after this weekends race. Until then...

Cheers, Terry Fair @ Vorshlag

Wow. Not sure how I missed this so far. Please more.

I'll pop on by and peek at the car this weekend. Sure looks cool.

Amazing work!

Nice writeup as always Terry. I think you may have even outdone yourself managing to work the composition of the earth's core into a tech writeup on roll cages.

I'm 100% with you on the mild DOM though, and yes - mounting seats is hell.

Dave, Terry and I had both worked for years using old, and incorrect info on chromemolly tubing as it applies to cages. Just in the last few years did we actually look at the changes and figure out there is rarely a good case to use chromemolly. Some organizations used to allow thinner wall tubing when chromemolly was used, which was supposed to allow for some weight savings while maintaining strength. Still, we preferred mild steel. But changes in DOM mild steel and more changes in almost all rule sets made the savings moot. There is no more weight savings to use chromemolly. You can gain a moderately stronger part, or cage, by using chromemolly, but at a greater material, labor and repairability cost.

Urge to buy beat C4 Rising.. Rising..

Fantastic update.

modernbeat wrote: Dave, Terry and I had both worked for years using old, and incorrect info on chromemolly tubing as it applies to cages. Just in the last few years did we actually look at the changes and figure out there is rarely a good case to use chromemolly. Some organizations used to allow thinner wall tubing when chromemolly was used, which was supposed to allow for some weight savings while maintaining strength. Still, we preferred mild steel. But changes in DOM mild steel and more changes in almost all rule sets made the savings moot. There is no more weight savings to use chromemolly. You can gain a moderately stronger part, or cage, by using chromemolly, but at a greater material, labor and repairability cost.

Yep. When the rule books caught up with reality the only reason to consider chromoly - weight savings - evaporated.

As others have said, this thread is fantastic! Please keep the updates coming!!!

I will probably have to sell my C6 this year in order to make more room in my monthly budget to allow me to buy a house/shop. A 92+ C4 is on the short list for a street legal track rat as a replacement. Thanks for sharing the details of your build.