Tonight I acquired the final piece of the puzzle for the exhaust I'm putting on my 8-valve, naturally-aspirated '85 900S notchback.
At Carlisle I purchased a lightly used 8-valve MSS header that had been specially ordered with a 4-bolt flange so that a turbo cat and cat-back exhaust could be used with it. At SOC I bought a brand new turbo cat and gaskets from one of the vendors. Tonight I bought a lightly used stock cat-back exhaust and test pipe that a friend ran on his '88 SPG for a few thousand miles before parting it out. Between all of this, I have $130 into it, not too shabby.
What I'm wondering is if there would be any performance gain from running a straight pipe vs. a cat? All along I'd been leaning towards a cat and was pretty happy finding a brand new one with gaskets for $30, then this straight pipe just fell into my lap. With the N/A 8-valve I need all of the help I can get. No emissions testing in Kentucky. Any opinions?
The debate isn't about back pressure. It's about the velocity of the gases. Big pipe= slower gases, smaller pipe= faster gases, but the big pipe with be able to handle a larger volume of gases at the same velocity as a smaller pipe.