How do you think it will sound? how much HP gain do you think that is.. i currently run flowmaster exhaust and love the sound but i want sound with the most HP possible help me out

 

Do you intend to put straight pipes where the cats are? I've never heard catless in person, but have heard some negative comments about the sound of cat-less fbodies. I know with straightpipes in place of mufflers you gain HP, but I don't know about cats. I'm sure though that it is probably a gain as well. As for how it sounds, look up http://www.ls1sounds.com/ (they don't have just LS1's), they probably have something similar to your desired setup.

FYI:I think hooker mufflers give the most airflow, that is, if you haven't already bought the magnaflow catback system.

 

I took my cat off when I had my manifolds and hated how my car sounded - really raspy. Now that I have my long tubes on it is no longer raspy and soundS really good, IMO. I have Hooker Super Comp. Long Tubes on my car with a Hooker Aero Chamber muffler.

 

I actually ran long tubes and a catless off-road y-pipe for awhile mated up to my Magnaflow catback. Normally, removing cats does add some unpleasant raspiness to your exhaust sound. However, the Magnaflow did a good job of cleaning up the exhaust note to the point where I couldn't even tell the cats were off. When I had a pair of cats welded into the y-pipe later on, I couldn't tell a difference in the sound.