I want to buy an American Thunder exhaust system from Flowmaster. The only 2 American Thunder sytstems are for a 5.0/5.7 with a single 2.5 inch cat, and for a 5.0/5.7 with a single 3 inch cat. I think both are designed for the TPI's. I have a 5.0 TBI LO3 engine, basically stock. Will the system designed for the single 2.5 inch cat fit/ work with my car even though it is a 91 RS? I think the system will fit the cat, but i dont know about the tubing leading to the muffler and the hangers. Or are the systems just designed to fit the z-28/ iroc-z. I called Jegs and asked a guy, he said it would but i just want to make sure before i go spending $320. Thanks for your help.

 

Don't worry buddy it will fit. Anything on the outside of the motor and the rest of the car is interchangeable between all the cars('cept fo the 6 popper). You can even buy 305 headers and keep them when you go toaa 350. I believ you will have to stay withe the 2.5 set unless you change everything including the cat, I am however not exactly sure about that. I am sure I will be corrected by daylight though. LOL
Scoty

 

Get the 3" system and try to get a 3" high flow cat at the same time. This will be better in the long run, then when you get the money or make the decision to swap on some headers you can get them with a 3" y pipe and you'll have a great exhaust setup for the 305 or a 350 of pretty high power levels. You'll be much happier in the end if you go 3" all the way.

 

I'm using the Flowmaster 3", dual 3" out (american thunder) system with a Catco (cheap) 3" cat and SLP headers and y-pipe.
Mine was originally a 305 tbi RS.
It's worth going to the trouble and getting the 3" cat.
made a big difference in how my RS runs and sounds.
Universal 3" cat with A.I.R. from Catco is only about $50!
-Rich-

 

Yep thats the thing to do is go with the 3 inch right now i just sent my order for the hedman 1 5/8 primaries with the 3inch collector.So then when i buy my hooker cat-back it will all be a nice big size for my 1989 Firebird formula 305 tbi which i plan to put a 350 in it in a year or 2. :rockon: :rockon: