How much difference does exhaust pipe size really make?

I'm finally getting ready to buy my exhaust system and was wondering if there is really that much of a difference between 2.5, 3.0 or even 3.5 inch pipe. I plan on installing the usual mods and want to make the right choice when I plunk down my hard earned cash. I am replacing the Y pipe back so any suggestions or experiences would be appreciated.

[tntcorvette]

if your car is stock, ide go with 2.5"

a too big exhaust system will cause a loss of torque, but mabey a smigen more hp.

[vettl83]

2.5" should work fine, unless your build up is going to be on the wild side. Then streetability becomes an issue. 84 CF 91 ZR-1 w/2.5" system.

[Raistlin]

I'm running hedman 1 5/8 long tube headers. My first exhaust was 2.5 duals, no cats. I picked up a lot of hp and tq everywhere (254rwhp, 354rwtq w/ AIR pump elim, K&N, cut air box, frisbee delete, porting to plenum only behind the throttle body)

The 2.5" pipes in the "kit" i got never fit right, so I ended up buying LT1 exhuast hangers and getting a local exhaust shop to make up a 3" dual system with an H-pipe.

I didn't notice any difference between the 2.5" and 3" dual exhaust. Some of this is probably do to the long tube headers, plus, the TPI has such strong low-mid range tq. I haven't been back to the dyno to get some hard numbers, but SOTP i'm not missing any low-end tq.

[EricVonHa]

The 2.5" should be fine for just over 400hp. The big thing is make sure the pipes are mandrel bent. Any of the aftermarket performance mufflers are fine. Choose your flavor. There isn't going to be any appreciable gains from one to another.

Thanks guys. Think I will stick with the 2.5. The car is daily driven and is not going to be too wild. Definitely don't want to give up any bottom end grunt.

[Redbob]

Like the guys said, 2-1/2" pipes should work fine, since the vast majority of the restriction or backpressure in your system comes from pipe transitions and catalytic converter and muffler internal restriction, very little from frictional flow resistance.

I made a 2-1/4" system for a stock '91 ZR-1 that sounded better than stock, reduced the weight by several pounds, and even lowered the system backpressure by 10%, since there was less of a "step" down (or up) from the pipe diameter to the muffler and resonator inlet and outlet bushings. I forget the exact figures, but this smaller diameter system picked up several horsepower.

Regards,
R

[Mad-Mic]

yeah you'll be fine with 2.5" pipe.

BTW sweet looking ride! i got the same car but with the 88-90 sawblade rims on mine i just love that color!

[scorp508]

You'll be fine with 2.5, but if you have future plans of big modifications might as well go 3" now and forget about having to do it twice.

[Redbob]

Sorta depends on how far you plan to go:
2 x 2.5" will be all you need for 475 HP or more on the street.
Going bigger at lower HP just makes the exhaust sound "trashier" - but by all means, if you want it to sound like Bubba's pick'em-up, then go as big as you can.
Just keep in mind that bigger = heavier, so when you're talking about microscopic horsepower gains for large weight increases, well, you figure it out.

Regards,
R

[Mad-Mic]

for every 100 lbs lost in weight you'll gain .10 at the track

[scorp508]

Guys he said he's replacing from the Y-Pipe back. That to me says he's not doing duals.

[Redbob]

Originally posted by scorp508
Guys he said he's replacing from the Y-Pipe back. That to me says he's not doing duals.

Exactly.
He's not going for maximum horsepower, and it would be senseless to put an exhaust suitable for a 600 HP race engine on a Sunday-cruiser Corvette.
The cost, the weight penalty, and the crummy sound is hardly justified by... no horsepower gain whatsoever , do you think?

Of course, if you just want the big pipe look, go down to Miguel's Mufflers and have him put 4" outlets on your mufflers.
Might want to get some 20" rims at the same time, and some of those valve stem caps that light up, maybe a little neon for underneath...

[KTA1000]

To through a wrench into the gears,, I seen a few of the Vette catalog companies offer a 2 1/4" true dual system, eliminating the cats for "off road only",,, they claimed 30 HP gains, could this be true? has any one used these? How do you think they would compare to a Cat back system? Too bad it's not a 2 1/2 system

Paul

[scorp508]

Originally posted by Redbob
Exactly.
He's not going for maximum horsepower, and it would be senseless to put an exhaust suitable for a 600 HP race engine on a Sunday-cruiser Corvette.

I hope you don't think I meant 3" duals.