I know a lot of third gens run full 3 inch, and a lot do 2 1/2. I was wondering if there is a performance deficiency if you use either or. Thanks for the time.

 

I been researching this topic alot lately i'm about to run my exhaust ..I found that it all depends on your setup and if your planning on running true duals or single. i'll be going with 2.5" so I dont loose velocity

 

I figure 2-1/2" is good, but 3" is better, assuming we're talking about 305 or bigger. I figure the better it flows, the better it goes. Just my 2c.

 

you might as well go 3 inch...

 

What engine you got??

 

3 inch is awesome...im haveing my 3" SLP catback and 3" catco cat welded up today...i need the 3"....im running 450hp at the fly...

 

it really depends what kind of setup you got. if you dont have a lot of performance mods and youre using a muffler bent y-pipe into a stock cat, i doubt there would be much of a difference at all. but, a 3" wouldnt hurt and you could use over in the future if you upgraded your car.

 

IF you wanna stick with single exhaust get 3'' unless you're pushin over like 450hp.

 

My LG4 was originally equipped with a 2.25 inch (I think) "Y" pipe. I replaced it with a 3" Y from an IROC. I gained all of nine horses (but keep in mind that 305 is bone stock except for a dual snorkel and an Edelbrock cat back exhaust). GM sells a dual-cat exhaust that is 2.5." That dual cat exhaust came with the HO 350 package. Take your pick.

 

I've heard the same. Good call, I think I'll make my decision on that note. Thanks fellas.

 

This is a non-issue if you want to make any kind of decent power. Go 3" or go home ...

 

The 3 inc one makes a much better noise too.

 

Okay, I may have not made it clear in my prior post so I'm adding this. That dual cat exhaust from Chevy is 2.5", but there are two tubes, so it is 2 times 2.5 inches. BTW, that dual cat exhaust may have been standard equipment on the 1LE. So, you have a choice between one 3" pipe or 2 2.5" pipes.

 

I may have oversimplified the issue in that post, wasn't really considering duals. But I'm sticking with the general statement.

 

I would go with 3" exhaust if you are looking to get every bit of power.
Even with the dual cat system it is not 2.5 x two pipes. It is only 2 pipes till they rejoin after the cat. The rest of the exhaust is one pipe from the intermediate pipe back to the muffler.

It is based on the bottle neck principle. The smallest restriction that you have is the maximum that the flow will be. Based on bernouli 's principle the reduction at the smaller section will increase speed but the volume will be reduced. Then when the flow hits the muffler and splits back to 2 pipes the velosity will decrease again, but the volume will not be able to go back to its original amount because of the reduction due to boundry friction that occured during the trip down the intermediate pipe.

This is why gm went with a 2.5 inch pipe after the cats in the HO unit not 2.25. However, they did not go for 3 because the engine power loss was not siginificant enough to justify the increase noise that would be a result of 3" pipe that they would have to try to tame and not cause more restriction.

If you have a stocker 305 2.5" will be plenty. Even if you have headers and a 2.5 good flow cat 2.5" will be fine. However if you mave some power in a 305 or a 350 3" cat back system, headers, and a 3"cat.

Thats my 2 cents.

 

Just remember that BIGGER is not always BETTER. You must design your Exhaust to compliment your engine combination.
By going bigger yo give up low end Torque and gain horsepower up top. With the smaller Pipes would improve Low end reponse but loose up top. Basicallly it all depend on what you are doing with your engine. If you dont spin your engine above 6000 RPM you would see minimal gain by using the larger pipes...