[LM93]

Considering putting an S475 sized turbo setup on my 350 that needs a rebuild from sitting for years. The car is a '79 T-top firebird, no numbers matching. It's going to be primarily a street car, cruising on weekends, driving to shows, and a road trip or two. Pacific Raceways is close enough for a day trip so hopefully I'll be able to make use of their road course on open-to-public days. I don't think the car is going to be competitive in any official event since it's going to be weighed down with NVH insulation, comfy seats, and hopefully A/C. Still, I want to keep up with the new muscle cars and I'd better buy my toys now while I'm still single. Turbo technology has come so far I think it's the better choice for me.

Aside from the engine and drive train, what kind of additions will my Firebird need to put that much power to the tires and not twist into a pretzel?
I am going to use subframe connectors, solid frame mounts, and g-braces, so should I consider an x-frame instead of regular connectors? Will new springs going to be enough or is something like traction bars a good safety idea to keep the axle under control? I've discussed roll cages with some people here and from what I've read the 1/4 mile times requiring one are something I'll have to work at passing so can I put off getting one until I'm sure I need one? GM 8.5 inch 10 bolt housings can take that much power, but will high quality 28-spline axles do too? I've read that C-clip eliminators can leak oil which isn't a problem for strip-only cars, but I'd hate to lose all my axle fluid on the interstate. I'd also hate to have an axle fly out on the track so if I ought to get some what should I be looking for? Going to change rear drum brakes for discs, will that help with axle retention?
What other mods should I be considering?
I'd like to do any cutting or welding now while the car is stripped down and getting rust repaired and before its new paint job,

P.S. For engines with big torque numbers, I've read that having one rubber and one solid engine mount is the best of both worlds. Is this true?

[johnta1]

I'd use weld in subframe connectors with the T-tops.
I'd also go with a 9" Ford rearend with the disk brake setup and with axle tube/center section bracing.
Driveshaft upgrade probably.


Calvert style rear traction bars may be needed also.

[ErikW]

This/\

[LM93]

Most weld-in SFCs are weld in the back, bolt in the front. If I use strong enough hardware and weld doubler plates around the bolt holes can I keep a removable subframe?
Now, is a Ford 9" suggested because a GM 8.5 isn't up to snuff or is it easier to set up with ladder bars and stuff?
Definitely going to need a new driveshaft.

[padgett]

a) jack up body
b) slide Art Morrison or similar chassis under.

[johnta1]

is a Ford 9" suggested because a GM 8.5 isn't up to snuff or is it easier to set up with ladder bars and stuff?

The 9" would handle the HP better. If you are adding the disc brakes might as well get a 9".
Stiffening the rearend is a lot easier with a 9" Ford. The stiffer rearend will be a great improvement on the setup. (axle tubes are easy to warp/spin/bend/tear etc on GM 8.5")

Most weld-in SFCs are weld in the back, bolt in the front. If I use strong enough hardware and weld doubler plates around the bolt holes can I keep a removable subframe?

The stiffer one can get the frame/subframe and body the better.
Bolts will loosen, by the time you figure it out the power will already have done the damage?
(voice of experience?)

[LM93]

Originally Posted by padgett

a) jack up body
b) slide Art Morrison or similar chassis under.

Are F-bodies really that flimsy? I was thinking I might need new rear frame rails but that's a whole 'nother level.

[HoneyHush]

All of the suggestions so far I agree with a 100%. The biggest thing you can do to add strength to the car is a good rollcage with good welds. Weld all the seems on the subframe and add bars from the cage through the firewall to the frame and it’ll be plenty stout.

[Tom Vaught]

Originally Posted by LM93

Are F-bodies really that flimsy? I was thinking I might need new rear frame rails but that's a whole 'nother level.

F-Bodies with T-Roofs Are VERY FLIMSY. Sub-frame connectors with not do much to save the T-Roof and after the car is warped good luck fixing that.
A well designed 10 point cage with swing out bars are about the minimum you will need to save the car if it is nice. Main reason why I bought a 78 Trans Am (with a regular roof) and installed frame connectors. And this was for a street car that was going around corners.

T-Roof, a lot of work unless you are just cruising to the drive-in with Wifey.

Tom V.

[LM93]

Well shoot, guess I was being a little overambitious. I don't want to lose much streetability. Putting a full roll cage in makes the rear seats useless and I'd be knocking my head on it getting in and out. Turbocharging will have to wait until I want a dedicated track car.

The bolt-in parts I was going to do initially should support a 350hp N/A build, so what would a 100-150hp nitrous shot need? I want to get a good idea of my options before I start buying parts.

[firechicken]

Skip the nitrous and go straight to the turbo. I did the nitrous first and filling bottles gets old and expensive quickly. With the turbo you can have your 150 hp with low boost and great reliability with room to grow as you break parts and upgrade them when you get power greedy.

[LM93]

Originally Posted by firechicken

Skip the nitrous and go straight to the turbo. I did the nitrous first and filling bottles gets old and expensive quickly. With the turbo you can have your 150 hp with low boost and great reliability with room to grow as you break parts and upgrade them when you get power greedy.

So, like a 5lb boost system? Use a smaller turbo and have plenty of wastegate potential? Can a T-top take the torque without a cage? I really want to keep the cab open and usable.
About needing an aftermarket chassis, if I take the stock subframe, re-weld all the outer seams, use Lab-14 products to do what NOT-A-T/A(don't know his name,sorry) did to the control arm mounts with the hardened washers and doubler plates, weld steel tubing to the rear LCA brackets and frame, use a Pro-Touring-F-Body sway bar brace and g-braces, how much power could my frame take, assuming I can get a rear frame is on par with the front? I can weld in anything, it's what I do for a living.

RideTech's 'TigerCage' looks super cool but the website emphasizes it won't work with T-tops. Don't know why it won't, or why it's made with 304 CRES and not cromoly steel. Which is too bad, the crossbar is removable and the door braces are tucked down towards the rocker panel. At 450-500hp I don't think I'll need a real NHRA cage for track day.

[firechicken]

Yes, if you don't want to cage the car then strengthen the frame as best you can which is a huge amount beyond how it came from the factory. Since racing is not a major use of the car for you, don't worry about the cage and either build the engine n/a to 450 hp or turbo it properly to get there with potential for more. If you want to go fast at a track you'll need at least a 6 point bar to start anyway so that is the deciding factor to keep the car from twisting. For me, I was going to go well beyond the roll bar rule so my car became a 2 seater by choice. The front can still be very user friendly with a roll bar good to 10.0 if done right.

[HoneyHush]

At 500ish hp you should be ok probably. I had a 79 Z28 with a 500ish 454 in it. T-top car with just frame connectors and SSM lift bars. It ran 11.50 at 117mph consistently with a slowish 1.50s 60’. It usually picked the driver side tire up a little when it left. I’m sure it was twisting up pretty good but I never saw any evidence of body damage or tops popping out or anything lol. Just an example to think about.

[Tom Vaught]

It never took me 500ish hp to run 11.55 @ 117 with my 64 convertible (3 point bolt in roll bar), and it had no roof BUT I did flex the rear quarters and had to have them straightened out by a first class body man years later. The 3 point roll Bar was only for the driver, not for chassis strengthening. This was at a newer track in a town in Missouri "Mid America Raceways" back in the late 60s. The pass was made with fresh 9" slicks and a 4 speed trans. They kicked me off the track shortly after that run.

A friend had a 1979 T-Roof TA and he pylon raced. His roof pieces barely fit in the car after that single week-end of racing. So the body WILL MOVE.

If the car is a beater, no big deal.

Tom V.

[HoneyHush]

That Camaro at the time put out 389hp to the tires on a chassis dyno so that’s why I said “ish”, because you know how different chassis dynos go lol.

Tom how heavy was that convertible? Had to be close to 4000lbs with you in it? I haven’t done the power to weight calculator but it had to making some steam? Or pretty rusty lol. Just kidding but with less power than 500ish would make them pretty flimsy if it’s wrinkling up that bad.

[LM93]

Asked for some ideas in the '79-'81 forum. They strongly suggested the roof-to-quarter panel be 100% welded. I didn't know there's only three spot welds from the factory there, yikes.

This might sound dumb, but I got to ask: If we're only concerned with stiffness and not meeting rules, would some kind of bar system that followed the outline of the T-roof help with keeping the body from flexing too much?

[Tom Vaught]

Originally Posted by LM93

Asked for some ideas in the '79-'81 forum. They strongly suggested the roof-to-quarter panel be 100% welded. I didn't know there's only three spot welds from the factory there, yikes.

This might sound dumb, but I got to ask: If we're only concerned with stiffness and not meeting rules, would some kind of bar system that followed the outline of the T-roof help with keeping the body from flexing too much?

I have seen and inspected a couple of T-Roof cars that the owner did just that.
He said: Its MY car, I can do what I want with it as long as the rules don't say I can't. Look at a 1965 Shelby Cobra with the most basic "Roll Bar" you could install on the car. a basic 2 point bar with a rear support.

A Front Hoop (around the windshield and down along the doors to the floor boards in the front, a front to back bar under the Center ("T-Roof Bar), and a Hoop behind the driver, with removable Door Bars. Most would not notice the stuff was even there. Lots of week-end racer SCCA guys with TAs modded this way. Most are the Pylon/Parking Lot racers.

You would still have 95% functionality of the vehicle.

Tom V.

[LM93]

So a t-roof shaped cage has been done before and worked out okay? That's good to hear, I'll look into getting one made. Can the front hoop be put close enough to the front seats to protect the driver without risking hitting you head on them in a collision when you're driving on the street with no helmet? Read alot of horror stories about people cracking their skulls on roll cages driving their track car without a helmet.
I'm not worried about rear passengers since I'm planning on getting three point seat belts for the rear seats. Maybe I can remove the rear set belts on track day and use bars that go from the rear hoop to the bolt holes in the package tray.

[GTOGEORGE]

Just make sure it’s done right and can be certified by NHRA. A cage is no good if it’s not safe!
I’ve seen too many so called bars and cages on so called street cars that wouldn’t be safe on a go cart.



GTO George