Chassis reinforcement - cages, frame connectors, etc.

[BuddyP]

Hey Guys, just trying to plan out the first portions of the project and would like so hear some opinions in the direction that I should go. Project is a '68 Camaro. Want to at least start out motor wise in the 400-450 range but want to build a chassis capable of holding 600-650hp (low boost Banks setup??). May do a LS1 swap with a future blower also (450-500hp??)...

But anyway, chassis is fully disassembled. I didn't want to get into too much cutting up of the chassis. Would like to keep it fairly close to original and also just don't have the fabrication facility or tools easily at hand. I currently have a set of CE bolt in frame connectors that I will probably weld in the rear but will still bolt to the front subframe in case I ever wanted to separate the subframe from the chassis in the future. Also have a set of Poly body mounts bushings. I have considered running cage tubes from the front of the subframe (welded on) to the firewall (bolted on). Would that alone with the frame connectors make a resonably solid car? Car would not be launched hard to speak of, and won't have the tires to do so (not tubbing, will have around 9.5" wheel and 275 tire). Also it'll be strictly street driven. Again, figure it seeing no more than an honest 500-550hp at most probably.

Just looking to go in the right direction.
Thanks!
Buddy P

[BuddyP]

ttt

[Norm Peterson]

I currently have a set of CE bolt in frame connectors that I will probably weld in the rear but will still bolt to the front subframe in case I ever wanted to separate the subframe from the chassis in the future. Also have a set of Poly body mounts bushings. I have considered running cage tubes from the front of the subframe (welded on) to the firewall (bolted on). Would that alone with the frame connectors make a resonably solid car? I'll start out by mentioning that I'm not all that keen on the idea of bolt-on SFC's, because if the bolts were to loosen you'd lose some stiffness. And this isn't in a location that's going to get much casual observation - you pretty much have to have it directly on your mind that you are going to look at them. It may be possible to work around this a bit by re-working the bolted connection so that a slightly loosened bolt would not result in the SFC moving.

Maybe this won't be an issue - but I guess that depends on the road conditions in your area and on the specifics of your driving what kinds of loads those bolted connections would see.

As for running tubes back to the firewall, you'd really want the tubes to pass through and connect directly to the cage where other tubes already intersect. Even the most rigid points on the firewall are nowhere near as stiff against concentrated loading as a continuous tube, and any local flexing of the firewall sheetmetal will tend to generate cracks. If you're unwilling to cut large holes in the firewall, you could perhaps back the engine compartment side tube up on the passenger compartment side with another tube and bolt the tube mounting plates together with the firewall sandwiched in between. This construction may give you a little more leeway for the passenger compartment side tube location, since it can be a little 'off' from being co-linear with the engine compartment side tube. The firewall can deal with loads in its own plane reasonably well, and that's what develops when the inner and outer tubes are not along one continuous straight line (and the "kink" is at the firewall).

Norm

[Mean 69]

One other key point here, the use of poly body mounts will will allow flexure between the subframe and the unit-body of the car. The points made above become even more possible in this case. Things are going to be moving all over the place, and eventually the bolt holes for the SFC's will elongate (or something else will break first, or both), and the firewall will likely become very distorted, or crack, etc. Use solid mounts, you'll be WAY happier.

And really, not to be a smart alec, but 550 HP in a strictly street driven car? That is basically where my car is, and even if I were to "only" drive my car on the street, with the performance potential, I'd HIGHLY recommend making the car as safe as possible first (passenger protection, brakes, handling), then add the power later.

Mark

[BuddyP]

Mark, Norm, it all makes sense. Like I mentioned above, I'm thinking big, but in the real world I'll probably never get there. What you have me wondering now is with all the people that are doing the subframe connectors, cages, etc, why even use subframe mounts at all? Why not just weld the front subframe directly to the body? Or do a lot of people do that? In all honesty, a LS1 with a blower or just a healthy SB (383??) looks to be in my future (400-450hp range).

Thanks
Buddy P

[jeffandre]

I believe NASA rules do not allow cage tubing to penetrate the firewall (haven't looked at the rules since Vince posted a link late last year). I recall reading that you would run tubes to plates on the inside of the firewall, then do the same for the engine compartment. If I do this I will bolt these plates together with some fat grade 8 bolts (may make a front cage that unbolts out of the way from 4-6 attachment points). Of course different rules organizations vary in their requirements, so check out what you think will apply and follow as needed. I chose NASA because they are fairly stringent and offered the most flexibility with the front part of the cage since I cannot have the tubes passing through the firewall.

I also used bolt-in sfc's, then had them welded out. They stick down some but after doing my minitub and spring relocation they are actually needed for spring protection (front spring eye is lower than stock, rear spring eye is higher due to sliders). I will weld the sfc's to the floor soon, as well as weld up the seams on my front sub (at least what I can reach easily, the sub us not removable now).