I've got an '84 S15 Jimmy for a daily. I put a 2.8L FI block out of a maro in it. It's got the factory 2bbl carb still on it(going to swap to the 2.8L MPFI asap).

Anyhow, I was reading about exhaust and the conclusion was that 3" pipe is too big. I agree since my Iroc has 3".

But if that is too big, why are the 2.8L headers that I see, have 2 1/2" collectors? The hedmans for my Jimmy and the PF&E for the thirdgen.s

If you run a Y pipe setup, if you put two-2.5" pipes into one pipe, shouldn't that one pipe be bigger? The next size up at MOST exhaust shops is 3". But now thats too big?

What's the point in having 2.5" collectors if it's too big too?

The hedman headers I want for the Jimmy are 1 1/2" primary, 2 1/2" collectors.

Now should I run 2 1/4" pipe from the headers into a single 2 1/2" back... or should I run the 2 1/2" pipe from the headers back into 3"?

I've got a 3" cat and 3" muffler sitting on my shelf that I'll be using (Exhaust on Jimmy is 220,000mi factory).

Confused?

 

i'd love to have 1.5" primaries and 2.5" collectors for my setup but, that's not stock. if you plan to keep your jimmy stock or nearly stock, i'd put 2.25" reducers right behind the headers then go into a single 2.5" or just run 2.25" duals.

 

The extent of it will probably be just the headers/exhaust.... and the fuel injection setup over the 2bbl.

Think the smaller piping sounds good too!