Frame bracing ????'s for full notch

[malibulvr]

Was having cage put in first, but been thinking about it and think it will be alot easier to do the notch and mini-tub before the cage is all the way in. Fixing to start cutting and want some opinions on just what will be enough bracing for the rear frame. I am putting 325/50-15 ET Street Radials under there and planning on cutting almost all the way to the inner skin and just boxing in the main rails. I took one of Elcorvino's pics and modified it a little to show the braces that I think I need to put in. They are the really bad looking yellow lines on the pic. The crossmember near the springs will of course go under the spring mount and between the shock and spring. The rear down bars of the cage will attach to this brace. The rear crossmember will attach to the frame where the rear body mounts attach to the frame and then will have triangulating braces forward. I need to know if this is enough bracing to race this car and do just a little bit of street driving!

 

[shotgun]

Before cutting mine I added new solid body bushings and tacked and piece of angle to the inside of the frame.

Not even done cutting here and you can see how thin it gets!

I then put in a brace like you have drawn from spring pocket to spring pocket. I would have prefered to do an X there but that would not clear 3" over the axle pipes,running full exhast.

I made a bolt-in brace that uses the rear bumper mounts to tie the rear together.

Last I would suggest doing this, brace the UCA mount, they tend to rip.

My down bars go threw the rear seat area to the bulkhead right behind the UCA mount for strength.
Also the "short" bars go to the LCA mounts which reminds me, weld a plate on top the the LCA mounts.
Think about where all the load is during a hard launch.

Now for MY crude drawing :lol:

Hope that helps.

 

[westexun]

The only bracing in my car is the crossmember for the anti-roll bar. I think if you built some support behind the notch where it gets really skinny right in front of the back bushing you could get by with just the anit roll bar crossmember. I only notched mine to the weld seem and put a piece of 10 ga. back in there, so I'm sure it's stronger than it was before I started. The only problem is it isn't enough of a notch to run a 10" rim, I'm gonna have to settle for a 28x10.5 on an 8" wheel. But I'm just shootin' for high fives or six flat eight mile times.

 

[boyzbad]

You need to support he front uca and lca mounting points and it won't matter what you do behind the springs. Everything behind the springs is along for the ride. This becomes an issue if you want the back seat but it's doable.

 

[westexun]

I plan on taking care of the upper arms mounting with the cage and I gusseted the lower mounts befor I had my frame powdercoated. I have heard of the lower mounts being driven through the floorboard.

 

[shotgun]

boyzbad, "Everything behind the springs is along for the ride." I used to feel the same way, but now know better.

I did some testing on a bare frame and also road testing. Adding a small brace helps these cars alot.

A small tubular or square tube at the bumper mounts really tightens up the car.

I am very weight conscience on my cars and shyed away from doing it, but added a hitch on the Wagon for towing and was blown away with how it effected the car.

The brace made a significant different in the way my race car twisted also. Makes chassis tuning easier, one less varible.

For the couple pound weight penalty, I say it is worth it.

Hey plus it's weight over the back of the car!

 

[boyzbad]

I have a bar back there for the chute I was refering to all the extras people add by the spring perches or even directly behind the tire.

 

[malibulvr]

Boyzbad, do you still have any pics from your frame notch job. I saw them a long time back but didn't save them. It would be wonderfull if you could post them for me.

 

[westexun]

Shotgun, you said a bar near the bumper made a difference. Does the car you're talking about have a cage in it?

 

[shotgun]

There are pics of 2 different cars ( Grand Prix and Cutlass) that I posted.

Not a rollcage but a rollbar.

But to answer your question, the pic of the rollbar is in the Cutlass that got the "bumper" brace also.

They don't leave much more level then this!