exhaust size for my 389?

[forsakenfew]

gonna have the exhaust done next week, and just curious what diameter pipe i should be running. it'll just be straight pipe all the way back. (gonna have dumps put in the front wheel well also)

the car is a 60 pontiac with a stock 389. no headers. is 2" ok? does a quarter inch up or down make ANY noticable difference?

[Tinbender]

Yes 1/4" makes a differance! (size matters!)You also get more wall thickness, so they last longer. Without mufflers 2&1/4" would be good. I'd go 2&1/2 with straight thru glass packs.
You can alter the tone with the last two feet of your tail pipes.

[forsakenfew]

thanks tinbender. the guy at the shop suggested 2.25. i had 2" straight pipe on my 62 olds with a 394 and ran it out with bellflowers. sounded great.

i'll go with the 2.25".

[tommy]

The stock manifolds will be 2" but you can weld 2 1/4 over 2" stub pipes bolted to the manifolds.

[draggin'GTO]

I've mated 2-1/4" directly to quite a few stock Pontiac exhaust manifolds, 2-1/4" will fit inside the stock 2" headpipe flanges and will clamp up and seal. I have also used 2-1/4" stubs after enlarging the manifold openings to the same ID as the 2-1/4" pipe and mated 2-1/2" pipes a few times with great results.

Your muffler man is right, 2-1/4" is a good size for a stock 389, even 2" would perform just fine. http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

----- Bart -----