85CutlassSupremeInSC

I'm trying to figure out if I want to run the duals on my project car running 2.5 inch pipe or 3 inch pipe...

I'm not sure which one makes more sense, performance wise or in general, since, from what I'm told, there is such a thing as opening up the exhaust too much...

The car is speced to have between 350 to 400 HP...

They will be true duals coming straight back from my headers, I already have my Flowmaster 40 series mufflers installed...

Oldsguy

I have heard the same about the pipe diameter being too large. I think 2.5 inch should be sufficient, 350-400 hp is not monstrous, I haven't heard of people going to 3 inch with that amount of hp.

85CutlassSupremeInSC

Well, I've been doing searches on different forums trying to gather more information about this and there are a few replies that say that anything over 350 HP will benefit from 3 inch pipes if you have an opportunity to apply them...

I plan on picking up the pipes sometime today...

85CutlassSupremeInSC

Here are some of the replies that I've read from other forums...

y2kthug
03-29-2001, 12:22 AM

They're actually pretty right though. Everybody thinks bigger is better. From my DSM turbo days, the real fast guys werent needing 3" exhausts until they were making upwards of 350HP. Seriously, there was no difference in ET's with 3" vs 2.5" for anybody under 350HP. And 3" will just be more expensive, weigh more, and give you less ground clearance. If you truly believe bigger is better, you shoulda bought a 5.7L V8 Chevy.

KC
03-29-2001, 04:43 AM

I'll just back up what Y2K said...

A 3" exhaust will gain you nothing compared to a 2.5" exhaust until you hit around 350 hp.

A 2.5" exhaust will also keep your exhaust a bit more quiet than the 3" and we all know how some states love loud exhausts.

So until you're hitting even a minimum 300 hp with the WRX, a 2.5" would be just fine.

Oldsguy

Well, I could be wrong, been so before. If you can fit 3 inch and feel they are right for your application, go for it.

But......why did you post the question if you had already planned to pick up the 3 inch pipes today?

85CutlassSupremeInSC

No, no...

That's the thing. I'm not sold on the 3 inch pipes. That's why I'm soliciting advice...

I planned on picking up whichever pipes were going to be optimal for my application after I did my research...

If you or another member here provided me with solid advice then I'd lean more towards the advice given. Or at least take it into consideration...

I just want to be sure I'm making the best decision...

Oldsguy

Oh ok, I see. Well, Oldsmobile advertised many of their engines at or above 350 hp in the late sixties and I don't think they ever used 3 inch pipes, for what that is worth anyway. As Norm has said, advertised numbers are just that, take if for what it's worth. I had 3 inch pipes on the '69 Delta I used to own and all they did was make the cabin loud at highway speeds.

85CutlassSupremeInSC

I found this while looking for more information about my question...

Just thought I'd share it...

http://www.youtube.com/watch?v=wAn8rgrcGRU

85CutlassSupremeInSC

Yeah, I'm thinking I'll stick to the 2.5 inch pipes...

Thanks for the info...

Rallye469

I think 2.5's are perfect for most builds.

That 350hp # is for a 4banger scubaru...
And that's rear wheel HP they're talking about.

350 RWHP would be about 430HP at the crank,
with losses from the accessories & trans.
That's how most of the old factory cars were rated.

Oldsguy

That's hilarious. Red Green is a funny guy. Haven't seen him on tv for a while though.

85CutlassSupremeInSC

Thanks for responding...

I picked up the 2.5 inchers...

Hopefully, I'll have them in by the end of this week...

The_Jeremiah

Go 2.5, a 3 inch pipe is almost too big to stick under a car. It wont sound that good either trust me i know. It will provide sufficient flow, and if your worried about it that much, go with some single chambers, or no mufflers at all. and if your running out of money, cherry bombs are cheep, last a decent amount of time, and provide almost no flow restriction

joe_padavano

I agree that 2.5" is fine, but I'll question the cherry bombs being "almost no flow restriction". Every test I've ever seen, most glasspacks are actually more restrictive than the Walker Dynomax.

The_Jeremiah

lol i just meant vs some of the cheap mufflers you can buy. personally no matter what your budget is i would go with some flowmaster single chambers they sound great.