Roll bar help (stop me from being stupid)

Hello, all, I'm starting planning on my 202X challenge X1/9's roll bar.

Build thread here

To be as succinct as I can, here are some details as best I can project them.

Finished weight, below 2000 lbs. 

Wheelbase:86.69" +/-

ET< 13.49

Convertible (no side windows)

Modified floor pan (I believe this is a big one) Modified chassis as well.

Engine swap PT Cruiser GT drivetrain

-What I'd like to do is a 6 point roll bar. Hoop, two diagonals going to rear shock towers, two side bars going forward to mid rocker.

Some more tubular bracing between the main hoop and rear shock towers would be really nice-can I do a partial tube frame trellis? The frame rails need pretty extensive mods for drivetrain fitment anyway.

-According to my research, I should use 1.75 OD .120 wall thickness tube (I'd like to stay with mild steel). Does the hive agree?

-Can I weld a firewall to the main hoop? Can I recess and weld it to my Targa bar? Does anything change if I weld a roof on? 

I'll try to find it, but I believe Patrick found a database where you could find pre-bent main hoops and order them cheap. I tried Jegs, will hit Summitt next and post here for posterity if I have any luck.

Here's a picture of what I am looking for in a main hoop if anyone just happens to know of one fitting these dimensions.

It's true, I draw like old folks berk, but, there you go.

All responses appreciated. 

Be well, everyone.

I don't know if you'll find anything that skinny. I believe these are the roll bar hoops that are challenge budget friendly - from competition engineering:

https://www.summitracing.com/search/brand/competition-engineering/part-type/roll-bars-competition/product-line/competition-engineering-8-point-roll-bar-main-hoop-kits?N=part-type%3Aroll-bars-competition&SortBy=Default&SortOrder=Default&autoview=SKU&ar=1

Now, I don't think there are any rules in NHRA that prevent you from splicing (meaning that you don't necessarily need a single piece hoop - which I know is big in many other forms of racing).

In reply to Robbie (Forum Supporter) :

I'd really like to avoid a splice. I'm reading some of those Competition engineering hoops as doable if I can recess them in the shell-something my Fiat book recommends anyway. 

  My other choice is buying a die for a tubing bender my buddy has, but I'm looking at how to do this with minimal personal contact. Plenty of other stuff to do in the meantime.

your "fiat book"? tell me more...

Published by Fiat Motors of America in 1979. Basically, a Fiat approved mod book for SCCA racing. They suggest you cut pockets in the frame for Lower control arm mounts, and raise the rack. Other zany suggestions involve bending a seat out of sheet, and mounting directly to the floor for a seat, chopping the windshield off, and yes, cutting the targa bar to slip the main rollbar hoop up that little bit higher. This is the same book that said you should use 12V to heat up wires that run around the windshield to soften the rubber gasket. It's got a great deal of information, some of which is applicable to my build, most of which is not. I'd be glad to share. I was so wrapped up in F-Dat and my own project, I didn't think to offer. There are patterns for heim joint mounts in place of the factory radius rod setup, Balance bar brake pedal, all kinds of fun stuff.

I just realized, there's a roll bar drawing, as well.

48" wide is close to the same width as the interior of a Miata. I have a roll bar that was removed from a Civic that is 48" wide, and another one from a Chevy S-10 that's just over 48". If you look around you can find stuff that will fit without creating a splice. Look at any small car as a possible source....Honda,Miata, early VW GTIs, etc. The ones in Summit for Civics and S10s appear to be wider by 3+ inches at the shoulder though.

You need the mustang 2 bar I believe, which is the narrowest one they have for cheap.  I will verify later, but whatever one is in the Wartburg is it, and it was something absolutely ridiculous like $47 shipped with amazon prime.  My car is so narrow i had to put big ratchet straps on the legs and pull it narrower

Thanks fellas.

The miata bars are right out. Not enough height, as they all seem to sit on the rear parcel shelf.

I'm finding Mustang II bars, but no dimensions. Jegs has them for 45 bucks, and says the box is 42.5X1.75X 46.25. Patrick, do you mind stretching a tape, please? Rough dimensions are fine.The X1/9 tapers in pretty hard at the top, but I imagine similarly to a MustangII/Pinto.

Warren, I'll look in to those, but the Civic stuff I was finding was just a bit too big.

I'm also reading .134 wall thickness. Is .120 a minimum? ie, is .134 legal? I imagine so.

All input is greatly appreciated.

Yes 120 is minimum so they do 134 because of variance in thickness.

if you go to summit's site you can keep selecting till you get down to just main hoops, and almost all have dimensions in the q&a

i'll check 

i did use the mustang 2 one.  It's narrowest at 50" at shoulders but i pulled it in to 48" with straps.  Part number C3126 

I think you may need the 2" square perimiter due to modified floorpan.  

https://grassrootsmotorsports.com/forum/2000-challenge/nocones-2020-challenge-build-thread/160484/page3/

We have a pretty vigorous discussion on NHRA cages for stupid modified cars starting on of 2 of my thread.

Basically it seems if your car required roll protection at all and does not have a factory floorplan the NHRA treats it like a tube frame dragster. For diagrams see the funnycar cages.

Section 21 pg 26

Unless an OEM framerail is located below and outside of driver’s legs (i.e., ’55 Chevy, ’65 Corvette, etc.) a rocker or sill bar, minimum 1 5/8-inch x .083 CM or .118 MS or 2-inch x 2-inch x .058-inch CM or MS rectangular, is mandatory in any car with a modified floor or rocker box within the roll-cage uprights (excluding 6 square feet of transmission maintenance opening). Rocker bar must be installed below and outside of driver’s legs and must tie into the main hoop, the forward hoop, frame, frame extension, or side diagonal.

I believe that's what Robbie ended up using for the bottom of the $2020 Datsun also.

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/datsun-roadster-2020-challenge-build/161581/page11/

In reply to Patrick (Forum Supporter) :

Got it! Thanks, looks good!

In reply to nocones :

You are correct that I made "rocker bars" below and outside the driver out of 2*2*.060 square tube. It seems .060 and .065 are both common sizes for 2*2 square tube as well.

Thanks, Nocones, I missed your post the first time around. I'm off to study, but will likely have questions later, if you're game.

Gumby is also familiar with x1/9s, and reads a rulebook with a good eye. Just in case you need more opinions ;)

In reply to Robbie (Forum Supporter) :

Yes, it is time to call a friend.

So, as near as I can tell, I need some kind of tubing up to the driver's left foot (same distance on the passenger's side, really). Modified floor pan- mine was gone, so obviously the case here. I need a front hoop, and maybe door bars (higher and more so than the angled pieces I had previously considered). If building a complete cage, materials can change. Basically, this is becoming a unibody AND a tube chassis car, right? 

To clarify intended use, I want to run the challenge, and the occasional autocross afterwards. Honestly the autocrosses afterward are optional. No drag races outside of the challenge, No track days. Just street use. Honestly, this is a kick in the pants, as I had ASSumed I could get away with a single hoop 4 or 6 point bar. Dope! Any advice/thoughts welcome.

I have been struggling with fitting some of these Challenge style, Frankenstein cars into NHRA's structure. The rulebook is laid out in an odd fashion that doesn't agree with my method of parsing information. I did finally find a PDF version so we can stop fighting with the horrendous e-reader for those who don't have a hard copy
https://nationaldragster.s3.amazonaws.com/Rulebooks/2020_NHRA_Rulebook_11_01/pubData/source/2020_NHRA_Rulebook_11_01.pdf

Section 21 gives all the safety regulations which are relevant to the Challenge, but does not include the requirements for when certain regulations should be implemented. The quick reference chart is helpful if you already understand the regulations it cites, but somewhat difficult to decipher for an outsider. Digging deeper into the book as a whole, I have found clarification of information from the chart scattered thru parts of various class regulations.

Section 4A pg.5 is pertinent to us

The language nocones cited(sec21 pg.26), applies to cars requiring a full roll cage. There is no language I have found which states all cars with modified floors are required to have a roll cage. As such, unless you are planning to go quicker than 11.0, I believe you are fine to build a simple 5 or 6pt roll bar(open top car 11.00-13.49sec).
You still have the factory rockers, be sure to tie into those. I see no issues with sinking the main hoop into the targa structure either. Firewall needs to be between the engine and you. If the main hoop is in that space also, there is nothing that says you cannot mount the firewall to the hoop. Frame between the main hoop and the rear of the car is open.

These guys will probably bend you whatever you want. At a guess they would sell you just a main hoop bent to fit. The rest of what you want should be straight. 

https://rollcagecomponents.com/

I really appreciate the feedback.

Gumby: Phew, I was having the fear that my challenge dreams were being derailed. This looks much better.

For any in the know: So, rules say the main hoop must be 1.75', 0.120 (0.134) wall.

Can the rest of the bars be smaller? The belt bar?

Does the bar have to be wider than driver's and theoretical passenger's shoulders?

1/4" thick reinforcing plates at all points it mounts to the chassis?

SFI 16.1 harness is good, right? Or can I run a 3 point factory (PT Cuiser) belt?

Read thru sections 21 & 22 in the PDF link above. All your answers are in there

In reply to gumby :You are the man. Thank you for all the help. 

Thanks to Gumby's hand holding, I've got answers. I'll share them for posterity.

Yes, SFI 16.1 is good on a harness. Good thing, because that seems to be all Jegs/Summit sell.

The main hoop, rear diagonals, and front diagonals have to be the same 1.75"/0.120 tubing. The cross bar/shoulder restraint bar can be 1.25"/0.118, but I'll probably just stick with 1.75"

1/8" reinforcing plates are good on my rockers/crossmember. I don't know what size, but will use the Fibinachi sequence to get them just right. 

Forward side bars must fall at halfway between the driver's shoulder and elbow.

This is kind of a big one: the cage must be at least as wide as the driver's shoulders or within 1" of the door. This may make the Mustang II hoop a no-go for me. 

Rear braces must be no more than 5" below top of hoop. crossbar cannot be above, nor 4" below drivers shoulders.

Grinding of welds is prohibited. Seat must be braced to the crossbar. Both doors must be functional from inside and out.

There's also a ton of harness info, along with other nuggets. Max of 12" soft fuel line, anyone? No flex pipe in exhaust?

Here's some eye candy that is way nicer than what I'll do.

wheelsmithy (Joe-with-an-L) said:

1/8" reinforcing plates are good on my rockers/crossmember. I don't know what size, but will use the Fibinachi sequence to get them just right. 

I don't know about the Challenge, but Lemons requires reinforcing plates to be 25 square inches minimum.  

In reply to Toyman01 (Forum Supporter) :

Good call. If I can't find anything conflicting, I'll go with that. 

I pulled the trigger on Competition Engineering C9408 from Summit, of course, even though I broke $100 for free shipping, I still got hit with a $40 boxing fee, so all in, about $100 hit towards Challenge budget. The local Metal Supermarket quoted me $77 for a 20' stick of 1.75/.120 tubing. 

OK. I've red and reread the cage section in that PDF and can't find the answer to my question.....how fast can a car with a 1.75" roll bar and a complete new floor /firewall go? I could put in a complete cage, but I'm short of material, so the roll bar option is preferred as long as the cage requirement doesn't come into effect at any ET I can hit.

In reply to DeadSkunk (Warren) :

I think cages are 11.5 for convertibles? Ie faster than most need to worry about.

edit, after checking the quick reference chart, the above is wrong.

convertibles need a bar at 13.5 and faster, solid tops need a bar at 11.5. Both need a cage at 9.99 or 135 mph, I think.

edit again, maybe the quick reference chart I looked at was out of date. Cage requirement might be 10.99 instead of 9.99

In reply to Toyman01 (Forum Supporter) :

Mounting plates are 6x6 .125 min. I was told 36 square inches does not have to be a square.  I tried to get the plate on at least two surfaces, like the floor and then up the rocker for added strength.