GRM Exclusive Reveal: Exocet Spec-A

Edit: We are incredibly thankful to have the community's direct input. You guys are an incredible resource with very diverse backgrounds and opinions, basically the best design review board an engineer could hope for. We consider the Exocet as a car designed by hoons for hoons, and this thread has already led to real changes in the final development and future plans. If you have any questions, suggestions, or other input, your voice will be heard here. Thanks again. -Warren

You guys are our most stringent customers, so the GRM Forums get it first. That's right, my handlers have given me (your friendly neighborhood Exomotive Engineer) the okay to reveal our big secret. We've only told a few key people (and already have sight-and-price-unseen preorders, funnily enough). This isn't even on our website or the MEV forums yet, so feel special.

Current UK-Produced LHD Exocet (bodywork remains the same):

We have spent the past few months redesigning the Exocet chassis from the subframes-up with modern CAD and FEA tools. Why the redesign? Well, the Exocet is already raging success in the UK, but the US market demands even more performance and perfectly streamlined assembly. The basic concept remains exactly the same: it's an easy bolt-on exoskeletal body for the Miata mechanicals, as seen here:

Miata mechanicals after unibody removed with engine hoist. (Image credit to FlyinMiata)

This new chassis has been made possible with a critical partnership with an industry-leading laser-CNC manufacturer based near our Atlanta headquarters. The tubes will be CNC profiled and bent, and the panels will be laser cut complete with mounting holes. The tubes have slots and tabs to ensure assembly precision and reduce our jig costs. All tubes are now DOM, too. There are no more bolt-in rollbars, a new shipping crate design allows us to ship even the base models with welded-in hoops. The Sport bar meets NASA, FIA, SCCA, and IMSA standards for vehicles up to 2500 lbs. Expected build weight should bounce around 1450-1500lbs with stock Miata components.

Here are some pictures detailing the new chassis:

[I'm trying to get the lower bar option as a "Stupid Tax" line item. Not flying with the marketing guys.]

We are in the manufacturing approval stage for the prototype and hope to have a running example ready in early January. A few measurements and a pre-powdercoat test-assembly will hopefully allow us to start full production before then. The question everyone is going to ask: HOW STIFF IS THAT, BRO? Well, it's improved. My last FE model was before the welded-in shear panels and a few tubes, but it was easily 3x as stiff as the original Exocet. I'm comfortable in saying that the Spec-A Sport model will be at least 4x stiffer than the original Exocet.

To some of you, that may seem like a ludicrous improvement, but look at the photos. The floor is now a fully stressed member, the propshaft cover is tied into the rear support structure, the rollbar is an integrated part of the chassis, there are new downtubes, the rear tophat boxes are active torsion loadpaths, the firewall is completely different and triangulated with a central welded-in shear plate, the engine bay is boxed in with gusset tubes, the rear bulkhead is newly triangulated, and the subframes are called upon to pull their share of duty, too. Another thing worth mentioning is the subframe positioning. The original Exocet tilted the subframes a degree or so relative to their original Miata positions. This chassis leaves them in the exact positions that they left, so your camber curves and other kinematics stay Miata-beautiful. Months of design has been put into this; the current chassis model is revision V (the letter, not roman numeral). That said, if you see something to improve, NOW IS THE TIME TO TELL ME. This is why we're announcing it here first.

Kicker #1: The Sport version will weigh within 5lbs of the MSA-spec original Exocet. Science.

Kicker #2: A fully integrated add-on cage option. It's prettier and a whole lot stronger. Updated stiffness data pending.

Kicker #3: The chassis was designed with V-8 swaps in mind. Yeah. That's right. We're working on a bolt-in LSx version, but until then, any of the tubular subframes available for the Miata should work. You'll have to figure out the transmission mounts, but that's not hard. Every part of the engine bay should be bigger than the stock Miata, and the rear gusset tubes still should allow a "rear-mount" V8 subframe. No guarantees yet, but the hood has been raised slightly and accommodates an LS3 in my computer model.

Kicker #4: The price should remain close to the current Exocet kit. We haven't nailed everything down yet, but every step was taken with production cost in mind. You should still be able to get one on the road for $10k invested.

All the bodywork remains the same as the original Exocet, but the rear shock mount boxes should now let you install the rear cover without any major trimming. The rear downtubes no longer prevent taking off the rear cover. New mounts are further back on the hood for Aerocatch latches, which we can add-on to your kit.

Salesguy Moment: Preorders available through info@exomotive.com

I personally have an engagement for the next hour or so, but I'll be back to answer all your questions. Constructive and/or objective criticism is very welcome on this post, no more apologizing for having opinions, guys.

Interesting...

make the body look like a mid-80s bmw e30.

but seriously, nice job on this so far. Will be interested in seeing the actual prototype, even if I can't get another toy at the moment!

I do like that updated design...

Guess I should have a heat to heart with the DMV as to what the rules in NV are for kit cars.

For those looking for state registration data, the SEMA Action Network has done a huge amount of legwork for you:

http://www.bipac.net/page.asp?content=tag_title_toolbox&g=SEMAGA

That looks nice, and MS looks to be a easy state to build a kit in. If I only weren't broke.

Very nice Warren! Way to go Exomotive guys. Thank you so much for sharing this with us.

Makes the exocet and even more likely 2013/2014 project for my miata

1500#...LSx...

SPLOOSH

That's fantastic!

That addresses a lot of the safety concerns I had with the original design. After wrecking a sport bike on track and dealing with the effects for months, safety is of the utmost importance for an HPDE vehicle for me these days.

That looks great. The rollbar is exactly what I had envisioned.

How about a substantial mount for an FIA seat and lower harness tabs?

Fuel tank mounting seemed to be one other sketchy part of the original. Is that addressed?

Schwing! Now I need to start looking for a donor miata and gathering an ls and transmission!

Uh wow!

And I was looking for another project to start when I get my first REAL paycheck! Amazing..

warrenv wrote: Another Top Secret: we're working on an internet-wide design competition for the 2014 Exocet's new bodywork.

BoxheadTim wrote: I do like that updated design...

It is definitely a big improvement.

BoxheadTim wrote: Guess I should have a heat to heart with the DMV as to what the rules in NV are for kit cars.

warrenv wrote: For those looking for state registration data, the SEMA Action Network has done a huge amount of legwork for you: http://www.bipac.net/page.asp?content=tag_title_toolbox&g=SEMAGA

You're on the right track. I was going to point out the sema-drafted laws that have been passed on a state by state basis. Since you're already aware of the laws, you know that in FL bodywork resembling a pre-wwII racer will allow you to build a car without having to worry about emissions

Excellent announcement. You've certainly piqued my interest.

One word of warning - someone will ask about mounting a Corvette transaxle. So check to see if it's possible. Oh, and nice CAD models of the GM parts!

This information is probably easily available elsewhere, but I'm going to ask. What's the F:R weight distribution of a "stock" Exocet build, both with and without occupants? My Locost is rear biased, but it's also got an engine that's been considerably pushed back.

Here's an idea: come up with a Spec rule set that uses as many parts from a Spec Miata as possible. Maybe the same shocks but a softer spring set? Might make an excellent next step up the ladder from Spec.

At least in the UK Keith they do run versions of this with spec miata or the NC version of spec miata

Whew, a lot to respond to. I'm very excited to see the positive feedback. It has taken a lot of work to get to the stage where we can publicly reveal the new design, and it's a relief to see that the community is excited for the same reasons we are. I think the Brits are going to be jealous when they realize how many cheap V-8s we have in the US.

neon4891:

Keep in mind that the LS, T56, and bigger diff will add 150-200 lbs to the car. Even then, a cammed LS1 will easily put down 400. At 1650#, you're at 4.1 lbs/bhp. You know what has a worse power/weight ratio? Veyron. Huayra. Noble M600. Enzo. Aventador. 430 gets you past a McLaren F1. Those are very achievable numbers for the stupid levels of possible go-fast.

Whee. I'm so excited about this, I put together a small list of common power/weight ratios so you can target your enemies: Exomotive Power/Weight Chart

z31maniac

Indeed. Safety is a top concern, especially when we've got so many customers planning builds with 200+ bhp. This new chassis is strong where it needs to be. The only thing I worry about now is how the rear subframe will behave in a rear-end accident, but it has a significant amount of structure back there holding it away from the driver. The mandatory downtubes and lower mount points should keep that rear deck from folding under. If you notice, the floor is now triangulated down to the seat mount rails. There are harness tabs that also work with stock Miata seatbelts, and the seat mount tubes are all 0.095" wall thickness. Frontal intrusion in a bit improved as well, especially with the full cage. The Race version will have 18ga welded-in steel floors rather than the riveted aluminum panels.

MattGent

I did a poor job of capturing them in the images, but there are integrated mounting tabs that work for Miata seatbelts and harnesses. The right driver hip mount is in the propshaft cover (with a backing plate welded to the inside), and the left hip is located at the bottom of the rear floor downtube. You can see it in the picture captioned "Plenty of headroom and egress room". Center tab(s) for anti-submarine strap(s) can be added on request. It's hard to put a standard one in there without knowing your seating arrangement. We thought about it, but we're not putting mount holes or through-tubes on the harness bar. Wrap-around harnesses are safer, lighter, spread out the load better, and make the upgrade a little cheaper to build. We don't want to penalize you for wanting to be safer. The prototype build will confirm our harness bar height, I'd like to keep the upper belts within 5 degrees up or 15 degrees down for all our customers. Some other kit car manufacturers mount the shoulder belts quite low, which is incredibly dangerous and can lead to spinal compression injuries.

The fuel tank is one of those "measurements" that we need to take from the prototype build. I'm not comfortable with the current solution either, and I suspect that the tank can be turned 'round 180 degrees and nested in a bit lower and closer to the subframe. It would make me happy if I could put huge gusset plates inside the rear deck tubes that double as tank mounts. I've been trying to think of a way to cold-form taco-gussets in a cheap repeatable manner without expensive tooling, but my best idea involves three big steel rods and a harbor freight press that can't guarantee an accurate bend. Oh well, gotta leave some future improvements...

JoeyM

I didn't know that. We have a lot of older customers that want something fun to toot around town, I'll have to hit the history books and find something old that looks the part. Every styling element was pretty much figured out by 1940, I'm sure we can pull a fast one. Even then, most of our customers leave the emissions control system intact. There's really no reason not to if you're using the stock ECU. A functioning emissions system doesn't suck up more than 1-3hp on the Miata; most of its work is done at part throttle.

Keith

Very glad to hear you like it. I follow your Targa exploits and even have your books stacked up next to Milliken, Gillespie, Haney, Rouelle, and Carrol Smith, if that says anything. The Corvette transaxle idea is definitely one we've got a roadmap for. Rear weight in a traction-limited RWD car is always a good thing (when your driver can handle it). Fun fact, we've got the Exovet trademark locked down for the time being, hopefully GM will let us run with it. ahem.

We haven't been able to corner weight one yet, but other builds have run up around 52-50% front weight. I haven't seen numbers with passengers. We played with the idea of offsetting the motor mounts to pull the front wheels a bit forward, but that would complicate the build dramatically (most customers keep the engine in the subframe) and increase the cost quite a bit. The passengers and fuel tank are significantly further back, but much of the weight in the Miata tub is in the rear. It also helps that you get rid of the front-located heater core, AC system, PS pump, and windshield.

The MX150R is a spec series in the UK under the Ma5da Racing banner. The MSA-approved spec is incredibly conservative and actually lets you to build a competitive MX150R for less than a Spec Miata ($10k vs $15-20k). They race with NC MX-5 Cup cars, and in an effort to keep them competitive, they are ballasted all the way up to 820kg with driver in an effort to let the NC MX-5 cup cars keep up. Of course it's still much faster than the cup cars.

http://www.youtube.com/watch?v=60vnVVlcLvg

We are in cahoots with a few rent-a-racer companies to get some new Race spec chassis on tracks around the US so we can get some feedback and data to develop a US spec.

warrenv wrote: JoeyM I didn't know that. We have a lot of older customers that want something fun to toot around town, I'll have to hit the history books and find something old that looks the part. Every styling element was pretty much figured out by 1940, I'm sure we can pull a fast one. Even then, most of our customers leave the emissions control system intact. There's really no reason not to if you're using the stock ECU. A functioning emissions system doesn't suck up more than 1-3hp on the Miata; most of its work is done at part throttle.

Understood. I was thinking more of the v8 conversions. In some places that gets tricky.

The SEMA documentation from the FL regulations at the link you sent earlier quotes the relevant regulation (FL statute 320.0863) at length. I just looked it over again, and it looks like you are not limited to those years. [I'm making a '32 replica, hence my knowledge about pre-war replicas and their requirements under the "street rod" registration.] It appears that any design that resembles a car more than 25 years old could be titled in FL as a "Custom"

FL statute 320.0863 said: (3) To register a street rod or custom vehicle, the owner shall apply to the department by submitting a completed application form and providing: (a) The license tax prescribed by s. 320.08(2)(a) and a processing fee of $3; (b) A written statement that the vehicle will not be used for general daily transportation but will be maintained for occasional transportation, exhibitions, club activities, parades, tours, or other functions of public interest and similar uses; and (c) A written statement that the vehicle meets state equipment and safety requirements for motor vehicles. However, the vehicle must meet only the requirements that were in effect in this state as a condition of sale in the year listed as the model year on the certificate of title. (4) The registration numbers and special license plates assigned to such vehicles shall run in a separate series, commencing with "Custom Vehicle 1" or "Street Rod 1," respectively, and the plates shall be of a distinguishing color and design. (5) (a) A vehicle registered under this section is exempt from any law or local ordinance that requires periodic vehicle inspections or the use and inspection of emission controls. (b) Such vehicle may also be equipped with blue dot tail lights for stop lamps, rear turning indicator lamps, rear hazard lamps, and rear reflectors.

In reply to JoeyM:

Well then, I think the exocet looks like a Lotus Europa. It's not terribly accurate but if you stand on one leg, lean to your left, and squint a LOT then you will see what I'm talking about.

With a full tank of gas and a driver, you may find you've got a pretty good F:R ratio. The transaxle would only help of course. The Corvette transaxle isn't necessarily the best choice, but it's a question we get a lot with the Miata conversions.

About my comment regarding Spec Miata - I don't think these things should be racing with Spec Miatas. I think it should be the next step up the ladder: cut your teeth in Spec, then yank the mechanical bits out of the tub and stuff them in an Exocet frame. Bonus points if you've just wrapped your Spec into a ball. Boom, you're in a more challenging higher power/weight class but you can keep all your investment in engine, tires, suspension, etc. Great stepping stone.

Then you add a V8 class that runs a crate sealed LS3 Better figure out where the wings will mount to the chassis.

Disappointed.

I dunno, a 480 crank HP LS376/480 crate motor in a sub-1700lb car might have similar performance

Looking very good. I have a self built 1700lb car that uses C5 Vette suspension, transaxle and a modified 500hp LS6 engine. It is the stock Vette wheelbase with the torque tube shortened to move the engine 23 inch rearward. The fuel tank is a custom made saddle tank that mounts under the very large backbone trans tunnel. It has 54% rear weight. I can tell you that the performance, especially handling, is quite outstanding. I made a simple T bucket inspired body for it so that i could register it as a street rod. Then i sculpted and made the body seen in my Avatar for it. The bodies are interchangeable and can be changed by 2 people in 30 minutes.

The Vette transaxle in my opinion is great. But, it requires that either the seats be moved forward or a very wide tunnel.

I built a Cobra replica and used all C5 parts. I couldn't use the transaxle and keep the Cobra body stock. So, I had a new input shaft made for the C5 diff and an aluminum adapter that bolted to the front of the diff. This allowed the use of a driveshaft. The diff bolts into the back of the stressed trans tunnel. In the Cobra I have an LS6 with a T56 transmission. This has worked great with out any problems.

If I were going to use C5 suspension again and wasn't going to use the transaxle I would look at using the aluminum diff from the new Camaro. It has mounts built into the housing.

Having fun. John

The engineering to mount the F-body T56 and a Getrag diff has been done, it should be a bolt-on for an Exocet other than the trans mount. And I'll bet the Exocet team could figure that out in about 5 minutes, it's not a complex part. The exhaust might not bolt on, but that's not a big obstacle.

The only reason I mentioned the transaxle is because it's a question we get once in a while. It's not going to happen in a Miata chassis.

Howling a torso does your 6'3" driver have? I'm not that tall, but I have short legs and a long body, so it matters to me. I like it, and have a rusty Mista that would make a beautiful donor. Oh, and I assume that there will be room under the bodywork for a hotside MP-62 supercharger?