Exhaust - GM Performance Tuning

awfulwaffle · #1 (**permalink**) 08-09-2007, 02:38 PM

Just a quick question, everyone. I am about to invest time and money into building a custom exhaust from the cat back, with a 4 inch muffler. Now, right before i got started, the buddy thats helping me with all this started raving about how i'll get decreased torque and low to no horsepower gain because of the diameter of the muffler. I was wondering if anyone could either confirm the validity of that or disprove it.

jeremy96gase · #2 (**permalink**) 08-09-2007, 04:38 PM

So let me get this strait. You want to do 4" pipe all the way, or just a 4" tip?

It would be best to do 2.25 or 2.5" pipe from the cat back. and a 2.25" or 2.5" muffler, then a 4" tip.

I did 2.25" pipe from the header back on my 3.1 Grand Am.

91parkave · #3 (**permalink**) 08-10-2007, 12:12 AM

yea 4' is for like 1000hp cars
2.5 is perfect ofr most v6 street apps your buddy is right listen to him

SL04P0PR · #4 (**permalink**) 08-10-2007, 12:15 AM

You're gonna want your muffler to match up to the diameter of the rest of your cat-back piping. I agree with the rest that 2.5" should be optimal for your car.

grandravermc · #5 (**permalink**) 08-14-2007, 05:00 PM

Nooo... I THINK he's talking about just what he said. (?) Not sure, but AwfulWaffle <-- haha, did you mean 4" MUFFLER diameter only? The piping itself surely wouldn't be 4". Just the muffler's diameter. (NOT the muffler's inlet/outlet diameter - but the ACTUAL width of the baffled part)...

I actually did the SAME exact thing. I had a 100% STAINLESS cat-back all custom made and welded on my car (ONE piece) w/ stainless welds, nuts, bolts...everything. But the guy HAND-MADE my mufflers which were STRAIGHT-THROUGH but 4" in diamter. The INSIDE of them had 2 and 1/4" piping with holes that were drilled into it, that were wrapped with fiberglass (to give it a DEEP, RICH but still a semi "Mellow" sound).

Check out the pics of it here---> www.cardomain.com/id/grandravermc

The RED Grand Am. Ironically, the PIPE size on THAT $550 set-up was ALL only 2". But with a 9.5 to 1 compression ratio 3100 V6 - there's no real advantage to 2.25" or 2.5". A QUAD 4's a TOTALLY diff story though!

awfulwaffle · #6 (**permalink**) 08-14-2007, 11:37 PM

Yeah, I did mean just a 4 inch muffler. 2.5 inch inlet, 4 inch tip. What my friend meant was that the 4 inch tip would cause torque loss, and i argued that as long as the rest of the pipe was the right size it would fit.