F41 and aftermarket bracing diagrams (MORE pics added)

84dragcutlass

Royal Smart Person
Supporting Member
Aug 20, 2009
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North Vernon IN
There is a box tubing section on the front of my racecar that i think was one heck of a good idea, it goes just behind the front bumper mounts and ties the frame rails together. It doesnt interfere with the core support or any other part that i can find when putting this thing back together. Way more structure that the F41 bars or similar on their own. Ill have to snag a picture of it
 
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ck1984

Apprentice
Sep 19, 2021
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There is a box tubing section on the front of my racecar that i think was one heck of a good idea, it goes just behind the front bumper mounts and ties the frame rails together. It doesnt interfere with the core support or any other part that i can find when putting this thing back together. Way more structure that the F41 bars or similar on their own. Ill have to snag a picture of it
This would be nice to see, i was thinking something similar like this front and rear, if i imagine what ur saying correctly.
 

Clone TIE Pilot

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Aug 14, 2011
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I have been seeing a big increase in people posting online that G bodies do not need reinforcing or that frame / body flex is a non issue. This could not be further from the truth. G bodies in mint condition with all the bolt on bracing can only take 400 HP before flex damage begins to occur. Getting above 400 HP you will need at least frame boxing, if not an aftermarket frame swap and/or roll caging. Of course the downside to increasing frame and body rigidity is decreasing the survivability rate for occupants in the car. The floppy frame is a primitive attempt at a crumple zone to help protect car occupants. Sucks there is such a trade off.
 
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pagrunt

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Sep 14, 2014
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I have been seeing a big increase in people posting online that G bodies do not need reinforcing or that frame / body flex is a non issue. This could not be further from the truth.
These non believers need to check out how much flex is in the frame when just dropping the engine & trans on a bare frame.
 
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Clone TIE Pilot

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Not sure if this thread already covered this or not but the ultimate frame brace is the body bolted to it. That is the frame and body work together to stiffen and reinforce each other. This is why having a complete set of good condition body mounts and their bushings is the starting place for reducing flex. Some G bodies have missing body bushings from the factory to tune ride comfort, its a good idea to install these missing bushings.

A little while ago I ran into a fellow G body owner who spent an fortune on suspension upgrade parts but bragged he still had original body mount bushings and how they do not need to be chaged even at extreme age. More likely he is too scared at what he may find, guess I can't blame him for that as body mount rot can snowball quick. Still, ignoring such issues will only allow them to become even worse. Moreover, body mounts are a safety issue as you do not want the body to seperate from the frame. Bad mounts will also prevent a car from handling at its peak. If the car is a rust bucket, better to find out before investing a lot into it.
 
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Clone TIE Pilot

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Aug 14, 2011
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Earlier in this thread I mentioned frame boxing the middle open rails which would greatly stiffen the frame. Probably more than anything else. Hellwig sells frame boxing kits for G bodies. However, frame boxing is not an DIY project, at least not an easy one. To do it right the frame most be stripped of the body, powertrain, and suspension and clamped into a chassis jig to insure it is square before you box it. The frame is flimsy and easy to flex out of square without a frame jig. You don't want to box the frame while its flexed out of square. Then there the matter of removing the factory wax coating around the weld area.

Even with a jig, its still easy to badly warp a frame from all the welding without carefull heat control. Many DIYs have F***ed up their frames attempting to box them. Back step welding should be used to reduce heat warpage. After that the frame should be measured again for squarness and pulled straight again if need be which is likely. Yeah there are lots of Youtube videos of DIY guys boxing their frames just on shimed jackstands and even resting on wheels, and most are either crooked or heat warped without the use of a jig. It doesn't matter how strong a frame is if its twisted.

It is possible to construct your own frame jig but again its not an easy DIY project. A frame jig must be large, accurate, rigid, heavy, and square. Overall, frame boxing is best left to a professional frame shop as they would still be cheaper than a mediacore homebuilt jig you may only use once. A jig made out of wood won't work either as wood is never straight and it moves with drying and humidity changes.

Simply welding plates to the open C channels does little to imprve the strength of the chassis, it will increase torsional stiffness a little. The better method is to weld another C channel to the middle C channel similar to old convertible frame construction. Boxing the frame this way will nearly double the width of the middle rails and greatly increase the moment of interia and the cross sectional area of the beam in the middle section of the chassis.

Some suggest adding roll cages to stiffen G bodies, which they due to some extent but their main purpose it to be a safety device for track environments but not street environments. But they have several practicality, safety, and legality issues. Basically roll cages are unsafe for street use as they require the driver to use a 5 point harness and helmet. Some states forbid roll cages and helmets on public roads and most racing 5 point harnesses are not DOT approved.
 
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