I have a 1990 GTA for my project car........well it used to be a GTA. My whole objective with this car was to make it a showcar with balls. I also wanted it to have something different about it. With my personal love for 3rd gens and this being my car since I was 18 I started the "re-do" process. I ripped out the motor and basically saved the block and built a monster of a 383. Haven't had it dyno'd yet but i figure it at about 550-600hp. Pulled out all the electronics in the whole car, and now running it with a carburator. Of course you know this also leaves me to re-doing the whole dash cluster too. (looking forward to that). Although many has said it was a bad idea getting rid of the fuel injection, I love the simplicity of it. That and it is soooooooooooo neat looking under the hood without wires running everywhere. Now the motor is in and running great and I had the whole engine compartment re-done, ripped out the heat/ac, relocated the battery so there are less visible wires, had the firewall smoothed and of course had it painted yada yada yada. Now I am moving into the chassis. I have a few questions about that and what seems to be a problem for everyone with the 3rd or 4th gen. Camaro/Firebird........................the exhaust. Here is what I am thinking: For the trans I think I am going to keep the 700r4 but have it overhauled. I am told with the right parts it will have no problems handling the HP. What do you think? Do you know of a shop with a good reputation? The rear is tough because I will be street driving it 90% of the time. I was thinking of the 9" but realistically I am not going to be towing it to the track every weekend so do I really need all that? Do you think the 12 bolt will be enough? I like the price alot better. I started looking at the BMR suspension and it "looks" great. Will my car "hook" when I want it too??? Dont get me wrong I will run the car on occasion...lol Now the exhaust!!!!!!!!!!! Damn this underbody!!!!!!!! I am not going to run cats. I hear mufflex makes a system to go from the collectors on long tube hookers into a 3.5in Y then back in the muffler with the 4"........ single out. Do you think the mufflex system will give me enough flow? Will I lose HP? I am open to suggestions and sound clips would help if anyone has similar amount of HP. God....true duals would be sweet. I almost considered going to a 4-link just to get 2 pipes over the rear. I also added some eye candy. Only thing missing in these pics is the braided hoses.

I am roughly in the same boat, but I'm not done with the engine yet (I just got the car about four months ago).

First off are your power figures. Are you running a high compression piston, or a wild cam with some monster flowing heads? Getting up to 600 on a 383 NA would typically require one of those. Most 383's end up in the mid 400's for power, but with huge torque. Anyways, I'll assume that's right for now.

A 700R4 will work, but you will need one of the better/best custom transmissions to handle that torque. Phoenix Transmissions or Pro-Built Automatics make something that will fit your needs, to the tune of $2000 or so.

For the exhaust, I would look at long-tube headers with custom dual 2.5" mandrel bent pipes. Do it right the first time, this car will need the dual system now or later.

A built 12-bolt or 9" would be highly recommended. The 10-bolt rear is good to 400hp, maybe, and that's with some beefing up. I'm on the fence as to whether I want to beef up my 10-bolt, as I won't be running slicks. You'll probably never hook up without slicks.

Just my slightly educated opinion. That's one hot looking engine, btw

I kept the motor at 10.5 to 1 compression so i can still run pump gas. Added world product Motown heads. Had them completely ported (intake/exhaust). The flow numbers were amazingly higher after port work, the guy that did it is amazing. The cam I really dont remember the specs off the top of my head but i know it was as radical as I could go to match the rest of the motor.
I have long tube Hookers on there now I am needing the collector back set-up. The guy who built the motor said dual 3.5 is what would be sufficient for my car. I am wondering about the single 4" or if they make a single 4.5". I have been told that flows better but that is up for arguement as far as I know. Go to my other thread in engine swap to see more specs on motor.

Don't see a problem running a Mufflex 4" system for a motor like that. If you want duals, run a 3" system.

Cross-sectional Exhaust Area

Single 2.25" - 3.98 sq in
Single 2.5" - 4.91 sq in
Single 3" - 7.07 sq in
Single 3.5" - 9.62 sq in
Single 4" - 12.57 sq in
Single 4.5" - 15.90 sq in

Dual 2.25" - 7.95 sq in
Dual 2.5" - 9.82 sq in
Dual 3" - 14.14 sq in
Dual 3.5" - 19.24 sq in
Dual 4" - 25.13 sq in
Dual 4.5" - 31.81 sq in

This supports the notion that a single 3.5" is equivalent to dual 2.5" pipes. I remember reading somewhere on this forum a thread that related flow to power levels, and that a dual 2.5" setup was good to 800 HP. I couldn't argue with dual 3", that's a pretty robust setup.

yeah true duals is something every third and fourth gen has issues with. There are a lot of OK ways to do it but in the end, no matter what, you are losing ground clearance, deing extensive floor metalwork or beating the **** out of it....who wants that. The ones that look good are only a soda cans height off the ground. I get scared about cracking my headers. I live in Jersey...lol....lot of shitty paved roads. Does anyone make a single 4.5"?
that chart is great thanks. What do you think I should do about my rear? 12 bolt built up or 9"?