Okay i went to a muffler shop to get a quote on how much it would cost to have them install and weld up a 3" dynomax cat-back and they said about $100. The guy told me that the stock exhaust on there was not much smaller (2.75?) and going up to the 3" wasn't worth it and that the 1/4" won't make much of a difference. Its his loss if i opt to just have a muffler put on ($40) so I don't think he's BSing me. Well now i'm going back and forth on this. Should i just put a muffler (dynomax ultra flow), or have the whole cat-back installed?

 

I was told the same thing. They ended up charging me $160. I'm not sure of the stock exhaust size, but when I added the cat-back (and this was going from no cat to a standard cat) I definately noticed harding pulling power starting at 2500rpms. Especially with you having an L98 I would go for it.

 

are you talking about the entire pipe going to 3", or are u just referring to the muffler?
Anytime you get a larger pipe, you have the ability to move more exhaust. Personally I would upgrade to a 3" pipe, especially since you have an L98, just to loosen up some HP.
If you are planning on doing some uprades to the engine, etc., IMO the 3" pipe is the way to go. Also, have the exhaust shop give you a mesurement of ID (inside diameter) of the pipe he's installing, compared to the stock unit that is on your car now. Like I said, I would just do the upgrade.
I had the entire flowmaster 3" catback system installed with high flow cats and i definitely noticed an improvement. Cost for the whole system, including labor, cats, was $450.00

 

man I have the same car as you, that is what I was told too. but the whole catback made a big difference. I noticed alot more pull power.