I didn't know weather to put this in this section, or the LT1 swap section...

I just did the LT1 swap. I'm using the LT1 exhaust manifolds, and the stock 91 Camaro RS exhaust for the stock 305ci. I was curious what kind of HP increase I could expect from an exhaust upgrade. here is what I'm thinking...

Hooker Headers
Dynomax high flow cats
Flowmaster series 50 mufflers
and all using 3" exhaust pipe.
and it would be true dual exhaust all the way back... maybe with an X pipe.

any ideas on cost of all this, and power gains? I was thinking it would cost around $800, and give me maybe 25hp? does that sound close?

 

actual HP increase to the wheels, I would not expect a whole lot. 25 HP seems a little out of range. 10-15 sure. the biggest difference you should notice is where your powerband moves to. a low restriction exhaust will flow very well throughout your rpm range and increase overall and avg Hp almost equally. This is what you should see. open exhaust will limit torque and push your powerband too far up in the rpm range. (automatics that shift on power development/vac/throttle pos. may actually shift past redline in some cases, due to less restrictive intakes and exhaust) and obviously stock is considered 'restrictive'. I can tell you that your cost estimation may be short some $$. but that depends on the quality of the parts you purchase. My set of headers costs around $550 alone. and 3" is expensive and not always worth the $. I've seen multiple flow comparisons of 2.5" vs 3" and it pretty much boils down to the size of your wallet, unless you are pushing 'THAT much HP'. another thing to consider is clearence. if you don't have the room to run it where you want it... out the sides, side pipes, or any other random place you can think of.
oh, and I don't know why but it's always recommended to run an h/x pipe.
I hope that gave you what you wanted, otherwise just ignore everything I just said