Convertible Vehicles - Convertible chassis mods

I've got a '99 T/A 'vert A4 with a stroker 383 making over 400 rwhp. I've done nothing to the chassis at this point. I've had it to the track a couple of times, running mid-12's (my exhaust system was stock). I just put in LTs and expect to break into the 11s. I'm worried about what I will be doing to my unibody - I don't want to bend it. At the same time, I don't want to go crazy with chassis mods that I don't absolutely need.

Also, what's with that X-shaped stamped-steel crossmember that also connects to the back of the transmission crossmember? I had to take the thing out for exhaust clearance. Does that thing add any rigidity to the chassis? It doesn't look like it could do much.

I'm sure someone will chime it w/ more details, but you need as a minimum subframe connectors (triangulated would be best), and a STB won't hurt. At those speeds, you'll probably be needing a roll-cage too in a 'vert. That'll probably do the most for stiffening up and strengthening the chassis.

That factory X-brace doesn't do much. You can leave it out w/ SFCs, it'll have to come out if you run a driveshaft loop.

Johnny speaks the truth. I added the SFCs and STB in my sig mostly to extend the life of my car. If nothing else, they will help keep the car from shaking itself to death.

A rollcage is really going to help keep the chassis in check. Besides that, a set of SFC will help tie it all together. Even if you don't do the cage, the SFC will add some stiffness to the chassis. A strut tower brace would also help.

I didn't notice much with the STB. I autocross mine, with also one HPDE under my belt and the car feels good to me. It's got fully adjustable read suspension, but I don't have subframes.

Tell us more about your goals with the car. If you want to pull the front tires with slicks, then yes, you will need to address it. However, if you are fine knocking down 1.8 60' times, I wouldn't worry too much about it.

As someone said, expect to get kicked out without a rollbar at some point if you continue to get faster.

My goal for the car is to run high 11's. I am actually pretty easy on the car most of the time and run standard tires on the street. I would probably just bring the car out to the track a few more times to get my 11-second timeslip for bragging rights. If I get kicked off the track, oh well. I would rather not mess up the top-down look of the car by putting in a roll cage. The car handles fine for me as-is.

My goal for the car is to run high 11's. I am actually pretty easy on the car most of the time and run standard tires on the street. I would probably just bring the car out to the track a few more times to get my 11-second timeslip for bragging rights. If I get kicked off the track, oh well. I would rather not mess up the top-down look of the car by putting in a roll cage. The car handles fine for me as-is.


I feel the same way. I put down 430 rwhp and I sit on 20s. My tire size is 255-35-20. I felt the biggest difference with the phb upgrade. i also have lcas and relocation bracket. The only other thing I am going to do is weld-in sfcs but its not a must. I have bilstiens and eibachs on all 4 corners as well. i felt the biggest difference besides the bilsteins was the hotchkis phb.

My car has 275/40/17's on it most of the time. When it goes to the track, it's wearing 26x11.5-17 ET Streets. Nothing big. Unless the consensus is that I'm going to damage the car at the track, I think I'll just keep the chassis stock for now.

Even if I never raced my vert I would not remove the SFC's! they really stiffened up the suspension!

I have a turbo 370 and still haven't done any chassis work.

I agree w/Johnnybs98WS6Rag...
First time I went to track w/sticky tires...broke the windshield from twist(and I only have 367 RWTQ).

Did the BMR SFCs (and the STB can't hurt). Car handles completely different :nod:

I don't feel you need to do anything. I ran into the tens with nothing done to the chassis
with no problems. I do have subframe connectors and a 6 point now for peace of mind.

I have also run in the 10's many times and 11's regularly... with no chassis mods other than removing the front sway bar... just saying . And your 400rwhp should easily get a high 11 with traction... my car is only 365rwhp n/a and runs high 11's @ 114. best wishes.

I have also run in the 10's many times and 11's regularly... with no chassis mods other than removing the front sway bar... just saying . And your 400rwhp should easily get a high 11 with traction... my car is only 365rwhp n/a and runs high 11's @ 114. best wishes.


I love seeing 10 bolts runnign 10s!

Do you have a cage? Like others have mentioned, I don't want one either.

I love seeing 10 bolts runnign 10s!

Do you have a cage? Like others have mentioned, I don't want one either.

They let you race in HPDE without a cage?

Or do you have rollbar?

SFC made the biggest difference on my vert