Just a quick one...
 

I have an '01 GT, I just got Flowmaster 40 series Delta Flow mufflers put on along with new 2.5" stainless chrome bullet tips. I know it's probably not much at all, but what could I expect regarding an increase in horsepower? If you've got any iput, I'd appreciate it. Thanks.

Not much , and to difficult to say. The real proble is all the restriction from the manifolds to the mufflers. Get rid of them and then your talking!

P.S. - I bet it sounds MUCH better!!!

Yah, I installed the same setup.. 2 flowmasters welded in.. it sounds a little better than stock.. no gain imo, but in 2 weeks I'll install a Bassani catted X, free up the exhaust, I cant touch the headers right now or I'll void the warrenty but I'll do that in a couple of years.. For you, you should do the headers, H or X or offroad pipe and flow tubes... It'll cost an arm and a leg but you'll love the gains and the sound.

No gain... although you'll get a different exhaust sound...

Re: Mufflers only
 

I had flowmaster 40 series mufflers on my 99 GT and the sound was great, the power increase was only modest.

On my 03 GT, I decided to get more agressive and go for the complete cat-back system with a shorty X-Pipe - Now we're talkin!

The other day i stayed with an O3 Snake up to 80 mph!!