How to stiffen the body without adding a rollbar ?

David Neibert

David Neibert

SCCoA Admin
While doing some stuff to get ready for WFC last night on my 91, we noticed some signs of excessive body flex on the roof sheet metal near the rear corners of the sun roof. It's not bad enough to call it wrinkled, but it's pretty close.

I refuse to install a rollbar in this car, but it looks like I will need to do something to prevent further damage. Does anyone offer a kit to weld to the subframe or whatever it's called to reduce body flex ? I need to get something done before using the nitrous or I'm really gonna have a mess.

David
 
what about some a rear STB? , and if subframes arent available maybe check if the KB jacking rails can be fitted in the SC.
 
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Dave, do you have a fuel cell or the OEM tank? With a fuel cell in the trunk I welded a bar that ties the rear frame together just in front of the rear subframe then two bars that tied the tunnel to that bar. Also I installed a bar that ties the two rear shock towers together in the trunk. Another thing I did was to add the non rear fold down seat V frame though I have fold down seats. These cars use the roof as a structural member and it would be nice to know how the thunderbird convertable concept car made up for the loss of the roof structure.
If it would help I can take pictures of what I did above.

Mike
 
Mike,

I do have the OEM tank and fold down rear seat. I don't really want to go to a fuel cell but I would be willing to install some type of v brace behind the rear seat. Whatever I do on this car will likely be required on the turbo car too, (also has OEM tank and fold down rear seat) but chances are pretty good that it will eventually get a roll cage so it may not need anything else under the car.

David
 
turbospeed said:
what about some a rear STB? , and if subframes arent available maybe check if the KB jacking rails can be fitted in the SC.
Click to expand...

Those may be my best option on the 91. Does KB make jacking rails for MN12s ?

David
 
Do you feel this is from the car trying to lift the front, or from a twist in the subfame? what type of rear limited slip are you running?

if both rear wheels are certain to be putting power to the ground. Then you'd expect the forces being applied is the subframe pushing up, hard on it's front mounts and pulling down on it's rear mounts.

If one rear wheel is leading the other, you'll get uneaven force but the same type, just with some twist.

Of course the whole subfame will also be trying to rip itself out from under the car.

So the question becomes, where can you distribute that force to that won't also create an issue?

I wonder if expanding the front mount's load point by welding a steel plate to the side rails, tying in the floor pan, then tie that into the front subframe mounts on each side. With the goal of spreading out the energy going into those mount points?
 
Mike8675309 said:
Do you feel this is from the car trying to lift the front, or from a twist in the subfame? what type of rear limited slip are you running?

if both rear wheels are certain to be putting power to the ground. Then you'd expect the forces being applied is the subframe pushing up, hard on it's front mounts and pulling down on it's rear mounts.

If one rear wheel is leading the other, you'll get uneaven force but the same type, just with some twist.

Of course the whole subfame will also be trying to rip itself out from under the car.

So the question becomes, where can you distribute that force to that won't also create an issue?

I wonder if expanding the front mount's load point by welding a steel plate to the side rails, tying in the floor pan, then tie that into the front subframe mounts on each side. With the goal of spreading out the energy going into those mount points?
Click to expand...

The rear subframe is also getting twisted trying to conteract the driveshaft forces, thus the car tries to rotate with the driveshaft.
 
David, I'll start looking into making the subframe connectors. If you want to try out a rear shock tower brace, I have those made up and ready to go right now.

-Rod
 
braces

Johnny Langton on TCCOA made some braces up. I have them on my car. It really stiffened up the whole car. He may still offer them.
 
racecougar said:
David, I'll start looking into making the subframe connectors. If you want to try out a rear shock tower brace, I have those made up and ready to go right now.

-Rod
Click to expand...

Rod,

What has to be done to install the rear shock tower brace ?

Mark,

Do you have any pictures of the stuff you got from Langton ?

David
 
I started making subframe braces a while back I don't know how to post pictures here,but if you pm me I will send you a link. The front braces really really make a difference. The rears seem to make a difference on launch,but other than that they don't do as much as I expected.
Alan
 
Mike8675309 said:
Do you feel this is from the car trying to lift the front, or from a twist in the subfame? what type of rear limited slip are you running?

if both rear wheels are certain to be putting power to the ground. Then you'd expect the forces being applied is the subframe pushing up, hard on it's front mounts and pulling down on it's rear mounts.

If one rear wheel is leading the other, you'll get uneaven force but the same type, just with some twist.

Of course the whole subfame will also be trying to rip itself out from under the car.

So the question becomes, where can you distribute that force to that won't also create an issue?


I wonder if expanding the front mount's load point by welding a steel plate to the side rails, tying in the floor pan, then tie that into the front subframe mounts on each side. With the goal of spreading out the energy going into those mount points?
Click to expand...

Mike,

It has a stock trac lock with 3.73s and all suspension is stock except for lowering springs and air bags. Car spins both tires, and seems to get good weight transfer and traction when using slicks at the track. No wheel hop either.

I can't really feel anything goofy with the car and it tracks very straight and is pretty easy to drive. The thing that confuses me is that even though the car is quicker with the AR than it was with an M90 and a 100 shot of nitrous, the car launches much softer with the AR, so I wouldn't have expected to see any signs of body flex until I started racing with nitrous again.

Then again the car does have a 100K on it and the damage may already have been done. When I'm installing the KB boost a pump I'll look for cracks in the sheet metal behind the back seat. I've never really given much thought to stuff like weight transfer and chassis flex, but it looks like I may have to start taking that stuff a little more serious.

David
 
David Neibert said:
Rod,

What has to be done to install the rear shock tower brace ?

David
Click to expand...

David,

I'll send you an email with the installation sheet that I send out with the braces. It's pretty simple, and I'll even help you stick it in if you bring the car over to my house.

Between the rear shock tower brace and the extra bracing in the roof and behind the rear firewall, the body of my XR7 is very rigid. I do want to build a set of subframe connectors for it so that the car is ready to handle more power in the future, so I might as well make up a jig to make the connectors for others.

-Rod
 
here's some pics

Here are some pics of what I have from Johnny Langton. Pics are from his car, but I have the same set up. I also have a brace that connects the shock tower area in the trunk.

FSSB-LECBRev2.jpg


frontoverallsubs.jpg


centercrossbracesubs.jpg


fssbfront.jpg
 
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These really stiffened up the rear of my car –but I guess these braces would be a bit to wimpy for your application. :)
(The lower connection in the centre of the car has later been modified to a more rigid solution.)
 

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I cant run that with my SC because I have the fold down rear seats. I want to keep it as CLOSE to factory interrior (until I am forced to put in a cage) as possible.

Chris
 
I bought a set of chrome plate jacking rails last year shortly after starting this post, but heven't been motivated enough to install them.

David
 
Can you post what the look like? I dont really like the way the subframe connectors work on these cars. I believe you can get more strength if you support from the mid frame, to the outside of the car (closesest to the ground effects....kind of like rock sliders on a 4x4), back to the rear subframe. I think there will be more strength gained from that and then a smaller bar tied into the center.

Chris
 
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