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roll bar advice needed

Old 03-10-16, 10:08 PM
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roll bar advice needed

So I'm about to redo my roof on my 87 t2, since the top is off, my friend and boss where saying,"this is the perfect time to build your own cage." I thought of it before they mentioned it, but really want my project going already. Those few words really got me thinking. He started looking in our metal pile and we have enough 1.75" .120" wall DOM. Best part is it would be $free.99!

So I can use the free 1.75" dom, but I always imagined using 1.5" in my fc if I were going to make a cage. My other buddy also mentioned to not really bother with DOM since I will not be professionally racing my car. Normally I wasn't cutting many costs on my car, but some important things came up.
so now I'm thinking
a) use the 1.75" dom at the shop, possibley have to buy a little more if I screw up
b) spend a little money and get some 1.5" dom
c) spend even less money and just get 1.5" tube

So after they mentioned it, I really started thinking about my design. I looked umder for a quick second and was thinking of the best way to tie my main hoop in with the rear crossmember mounting. Anyone have any good ways to do this? From just looking at it for 1 minute I had a few thoughts. Remember I only glanced at it for a bit and thought I would consult you guys to learn.
1) cut some of the material to try to reach that mounting point. This didn't seem too great of an idea because it looked like that whole raised beam area looked like it was a pretty structural part of the chassis.
2) make my base plate where all the bolt-in roll bars go, at the floor right behind the seats, through the floorboard. BUT I was thinking of making my base plate bigger with a bend welded to that raised structure to tie it in.
I need to look at it again, So far I'm thinking more towards my first option, but really planning out what to cut and weld.

So for my rear mounting I was thinking of going straight to the shock towers. Anyone have another area they would recommend?

This will probably delay my project for another month, not that I'm in a rush. I want to TIG weld my cage, I'm keeping my fingers crossed that my tubing notches are nice and tight fit. This sounds like a fun project, but I need a good plan first
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Old 03-10-16, 10:24 PM
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I knew I remember seeing something about the subframe bolt!
https://www.rx7club.com/2nd-gen-arch...e-bolt-518333/
What do you guys think about making my base plate tie in with that?
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Old 03-11-16, 03:53 PM
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You need to use either 1.75x.095 or 1.5x.120 DOM or seamless tubing, because the minimum race weight for an FC in any normal class is ~2600lbs.
Going to all the trouble of building a cage and having it not comply with the SCCA/NASA rules would be a dumb decision. It doesn't take much more effort to do so, and it leaves you a lot more choices in the future.

All else the same, 1.75 will be stiffer than 1.5, so if you have the head clearance and the right die, do it.

You can take a look at my thread on our ("Atomic Wankel Racing") endurance race car build a few threads below this and see how we designed our cage. There are lots of ways to do it, but ours is one option. Keep in mind some of our decisions were based on the ChumpCar rules, which limit how many tubes you can use and where they are allowed to attach.
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Old 03-11-16, 09:16 PM
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Originally Posted by patman View Post
You need to use either 1.75x.095 or 1.5x.120 DOM or seamless tubing, because the minimum race weight for an FC in any normal class is ~2600lbs.
Going to all the trouble of building a cage and having it not comply with the SCCA/NASA rules would be a dumb decision. It doesn't take much more effort to do so, and it leaves you a lot more choices in the future.

All else the same, 1.75 will be stiffer than 1.5, so if you have the head clearance and the right die, do it.

You can take a look at my thread on our ("Atomic Wankel Racing") endurance race car build a few threads below this and see how we designed our cage. There are lots of ways to do it, but ours is one option. Keep in mind some of our decisions were based on the ChumpCar rules, which limit how many tubes you can use and where they are allowed to attach.
Cool, thanks. I never knew that the 1.75" .95"wall would be stiffer than the 1.5" .120 wall. Was it part of the rules to not allow it to meet at the strut tower?

I don't plan on doing any professional racing. I am merely a mechanic/fabricator and like to build stuff here and there and my fc is for practice and fun
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Old 03-12-16, 06:53 AM
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Originally Posted by GrossPolluter View Post
Cool, thanks. I never knew that the 1.75" .95"wall would be stiffer than the 1.5" .120 wall. Was it part of the rules to not allow it to meet at the strut tower?

I don't plan on doing any professional racing. I am merely a mechanic/fabricator and like to build stuff here and there and my fc is for practice and fun
You will be glad one day when you sell it as a roller with a cage that conforms to governing racing body rules. It will sell faster and for more $.
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Old 03-12-16, 11:50 AM
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Originally Posted by ZoomZoom View Post
You will be glad one day when you sell it as a roller with a cage that conforms to governing racing body rules. It will sell faster and for more $.
good point!
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Old 03-12-16, 02:09 PM
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So I bought round dom tubing, 1.5" x .120 wall. I got the price difference between the tubing I was looking at.

Welded steel tube 1.5" .120 wall 20ft=$38.00
Dom tube 1.5" x .120 wall 20ft = $59.36
chromoly 1.5 x .095" wall 20ft = $118.40
I looked at rules, and I believe a car over 2500# would still require .120 wall chromoly. I should have gotten pricing on .120 instead of .095
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Old 03-14-16, 01:45 PM
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Cro-mo cage has to be tig welded - no mig welding allowed if you want to pass any race tech.
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Old 03-14-16, 02:06 PM
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Originally Posted by DaveEstey View Post
Cro-mo cage has to be tig welded - no mig welding allowed if you want to pass any race tech.
Yeah, I just went with the dom. For my 4 pt roll bar, there would be barely any weight savings if I went from .120 to .095". I think from reading rules, even if i went chromoly, I would still need .120 wall. I will be tig welding my cage regardless
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Old 03-17-16, 12:28 AM
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so I'm trying to think of the best way to make my base plates for the main hoop. That area the subframe is right above is angled quiet a bit. I'm wondering if anyone has any pictures or good ideas

I was thinking about the flat off the top of the subframe, and going outward with a 90 degree bend. The front would bend down , and the back would bend up. My doubts are that right under the plate where the bar would be , would be hollow about 1/4". Although I know lot of people build raised boxes with 1/8" plate, so they can drop it down so they can weld the top.
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Old 03-23-16, 10:54 PM
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So I made the plate for my rear strut tower out of 1/8" steel. One at the top with a bend. I tried to make the piece wrapping around the tower in one piece and with tabs bent to tie it in with the chassis a tad more. The last 25% of it wasn't lining up well so I chopped it and welded it on as another piece.
Some of the gaps weren't as nice as i wanted. I wanted to leave about a 1/8" gap so my welds fused the chassis and the plates. I'm hoping the passenger side will come out better. Learning from my mistakes



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Old 03-30-16, 11:50 AM
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So I made one of the base plates for my main hoop. This was actually easier than the rear shock towers. That wrap around with bends on it was hard to do in 1 piece. That's why pay off it had to be cut and redone, so it became 2 pieces.
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Old 03-30-16, 03:19 PM
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If you want to race with SCCA I think the rear mount has to go to the "frame rail" (boxed section of rear wheel well area).

I believe that the rear shock tower is not allowed.

This is the problem that the Raceshop roll bars for the FD RX-7 and now the Samberg roll bars that loosely copy it have.

I think I heard the Raceshop owner got into it with SCCA over this subject...

Which is a pity because those are the roll bars I want for my FD!
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Old 03-30-16, 04:09 PM
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Originally Posted by BLUE TII View Post
If you want to race with SCCA I think the rear mount has to go to the "frame rail" (boxed section of rear wheel well area).

I believe that the rear shock tower is not allowed.

This is the problem that the Raceshop roll bars for the FD RX-7 and now the Samberg roll bars that loosely copy it have.

I think I heard the Raceshop owner got into it with SCCA over this subject...

Which is a pity because those are the roll bars I want for my FD!
I'll just be taking my car to the track on the weekends. Darn rules!
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Old 03-31-16, 11:19 AM
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do like we did and put the rear stays tangent to the shock tower. That way you still reinforce the shock towers, but also meet the 'frame rail' rule.
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Old 03-31-16, 11:34 AM
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Originally Posted by patman View Post
do like we did and put the rear stays tangent to the shock tower. That way you still reinforce the shock towers, but also meet the 'frame rail' rule.
Do you have any pictures? I'm trying to get ideas. I just finished my 4 base plates. And the more ideas the better
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Old 03-31-16, 04:00 PM
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next thread down- AWR endurance racer
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Old 04-01-16, 11:01 PM
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Nice looking welds!

What kind of racing do you want to do?

The SCCA treats moly and DOM the same with respect to wall thickness and diameter so there is no advantage to using moly from a weight savings standpoint. ERW tubing is only allowed on grand fathered cars that were built when it was an allowed material.

For the record, 1.75x.095 or 1.5x.120 tubing is required for cars weighing more than 2700lbs. For cars weighing less than 2700lbs you can use 1.5x.095 tubing. Note that the tubing spec is for the required tubes in the roll cage - main hoop, A Pillar bars, door bars, main hoop bracing, etc. So additional tubing can be made out of lighter stuff. Finally, 1.75x095 DOM is lighter per foot than 1.5x.120 DOM and it does spread loads out a little more. However, 1.75 diameter tubing is harder to work with in a small car.

You can get a free download of the SCCA General Competition Rules (GCR) here Cars and Rules - Cars and Rules - Sports Car Club of America Starting on page 108 of the April version of the GCR general roll cage requirements are explained.

The GCR covers cages for wheel to wheel racing cars - the various rule sets for SCCA open rack and TT events can be seen here Time Trials - Time Trials - Sports Car Club of America For these forms of motorsports a cage may not be required at all. But there is nothing wrong with being safe

SCCA cage rules are very similar to NASA's but NASA is a little stricter with respect to bracing within the plane of the main hoop.

Here is my build https://www.rx7club.com/build-thread...-build-992966/
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Old 04-06-16, 01:46 PM
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A 4 point roll bar is legal for SCCA Time Trial events, but it is not legal for SCCA road racing. A Full cage is required for SCCA road racing.

The bar must also have a diagonal cross brace.

It is recommended to have a lateral cross bar to tie the shoulder harness to. Running shoulder harness over the driver and back down to the floor is not allowed, so that is why it is recommended to have a lateral cross bar to secure the shoulder harness straps.

I do hold SCCA Time Trial and Road Racing Scrutineer Licenses.
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Old 04-06-16, 02:19 PM
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I do hold SCCA Time Trial and Road Racing Scrutineer Licenses.


Very nice!

Could you please tell me if there is any bearing on what I said about the 4 point roll bar mounting for SCCA Time Trials (Solo) events?

Meaning-
I have heard that the two rear bars are not allowed to mount to the rear shock tower tops since mounting at the rear shock towers is deemed as providing reinforcement to the unibody (instead of just a safety function).

The RaceShop and Samberg bars I favor for the FD mount the two rear bars to the rear shock tower top.

The other FD bars mount a bit further back through the wheel arch.
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Old 04-07-16, 09:13 PM
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The SCCA Time Trials rule book does not prohibit you from attaching your rear down braces to the rear shock towers. Personally, I recommend tying together all the important points of the chassis, like you are trying to do.

From the below site, select Track Trials and Hill Climb Rules
https://www.scca.com/pages/time-trials

We have an active Time Trials series in the Southeast Division of SCCA. We are having an event at Talladega Gran Prix Raceway this weekend.
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Old 04-09-16, 03:16 PM
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So I bent my first main hoop with JD square model 4! Works great. I watched a video by wyotech with a guy that speaks in monotone. Very informative , but my buddies and I like to laugh about it. I could imagine falling asleep in his class. Did the measurements and found ways to measure the tangent vs eyeballing it.
Anyways, here is my main hoop mocked up with a bungee. I want to keep my headliner because my plan is to weekend track it, or be a poser. Jk, I like doing this stuff, and I have tools at the shop. So while my roof is apart, im trying it.



It will be a little lower afteri figure my headliner situation
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Old 05-05-16, 11:26 PM
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So I made some progress! Welded in the main hoop, and the rear kickers. I mocked up my seat and it seems like my harness bar will need to be mounted slightly further back






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Old 05-05-16, 11:29 PM
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So I made some progress! Welded in the main hoop, and the rear kickers. I decided to get some practice with the tig. The base plates are mig welded because Iof the dirty chassis. I mocked up my seat and it seems like my harness bar will need to be mounted slightly further back







I'm debating on how much further back I should make the harness bar. Right now my seat is about 3.5" from the main hoop. What's a good distance?

Last edited by GrossPolluter; 05-05-16 at 11:31 PM.
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Old 05-07-16, 03:52 PM
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Finally done!
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