I am running a 3 inch exhaust with straight through silencers (2) behind a GT28RS and the noise is unbearable . If I go back to a 2.5 inch exhaust with similar silencers will it cut the noise and allow enough flow for 300 whp ? Thanks A.

I doubt the 2.5" will let you breathe well enough to make 300. What are you using for a muffler? Adding sound insulation (dynamat) helps a ton.

You should replace the 2nd silencer with a proper muffler. That will help a lot with the noise. Do you run a test pipe? I have an extra resonated test pipe that would quiet things down a little more. Its not quite 3" but its very close (I guess its metric or something).

Test pipe ? This is not a term I'm familiar with . What exactly is it ?

A test pipe is just a straight through pipe (sometimes perforated as mentioned) and goes in place of a catalytic converter...basically you eliminate your cat. and you remove a lot of restriction from your exhaust which=more power. Illegal in most states for use on the road...

-Travis

Get a good muffler annd sound-deaden the trunk.

actually, the cat makes a pretty good muffler by itself.

put a 3" magnaflow oval on there, 18x6x4 or whatever. they're like $60 and it will be MUCH quieter.