Alright I know The 91 RS's were stocked with very restrictive intake and exhaust manifolds. I've got the money for the exhaust system now but not for the exhaust manifold. Is it possible to have my exhaust installed w/ high flow cat, 3 inches all the way back w/ the stock exhaust manifold, and then later upgrade the exhaust manifold w/out making any alterations to the new exhaust system? Also, while I have the new exhaust and the old manifold, will there be even a small amount of performance gain? I'm just trying to cover all the bases before I make a decision. Everone here wants around $475 for Flowmaster catback exhaust, does that sound right too?

 

You could do it that way but I'd rather go with 1 3/4 headers if a 383 is in the plan for the future or 1 5/8 headers if not. SLP makes a good one. You could do exhaust first but the gain will be minimal if any at all because I believe the choke point is in the manifold. Do this test. Make a couple of runs and disconnect the exhaust system from the cat back and see if it works any better. Make sure that if you remove the exhaust, you keep it in the car to keep the weight consistant. If you see no increase, you won't see it with the cat back system.

 

Sounds good, I'll try it after I get off work tomorrow. But even if there's not much difference in the performance is it possible to change the old manifold later w/ out doing anything to the newer exhaust system?

 

You have 2 exhaust manifolds. They connect to a Y pipe, that connects to the cat. The intermediate pipe connects to the cat with a ball and flange type connection. Then it goes into the muffler with 2 exits to the tailpipes.
If you buy a catback, it will hook up with no modifications, welding, etc.
Keep your stock cat until you get headers. Or you will have to cut and weld it again.

 

I had dual cats but I changed them out to the single cat version. My exhaust is set up like a stock one except there is no air injection to the cat. also, it is possible to take it all apart because nothing is crimp clamped down. I am using an exhaust band at every joint and it can easily be removed.

 

That's good to hear. I was thinking of going to a wrecking yard and getting some Z28 manifolds. Just a thought but could some old Corvette exhaust manifolds go on an 3rd gen F-body? Did those have two manifolds too?

 

You have 1 intake manifold and 2 exhaust manifolds. That is the log shaped thing that leads the exhaust charge into the Y-pipe. You will be changing it from the cat back so why bother with another manifold?