My motor is basically stock and I'm runnin' the stock y pipe with gutted cats, magnaflow 3" in/out single with 3'' mandrel bent tailpipe and a 4''x18'' chrome tip. I love thins system!

 

So 3" pipes from the LT headers to the exhaust tip would be great on a FI LQ4 huh?

But how loud?
back pressure loss?

 

I have been "told" and I have also heard that a single 3 inch will scavenge the exhaust better than any dual setup out there.

 

Well I'm still kinda 50/50 here, its about half n half, so I guess ima flip a coin lol

 

go for single 3". thats what all of the major brand exhaust companies go with...if your going true duel use 2.5". no point in trying to re-invent the wheel

 

go with the 3" exhaust, i personally have a 3.5" exhaust on my 98 silverado. I think the 3" has a good sound to it and has good flow.

 

hmmm, damn its still kinda 50/50 man this sucks now im more confused, ima ask the muffler shop doin it for me, see what they think, i dont wunna buy 3'' hi flow cats and 3'' mufflers and then not like the performance, but then i dont wunna but 2.5'' cats and mufflers then have to replace it when i get a LQ9

 

Im a little unclear
are you gonna be running a dual setup?
I assumed duals


I think you would be fine with a 2.5 system on the stock LQ9.
But if you did more to it Im not sure where that point is that the 3" would benefit or... how much it would hurt if it stayed stock

like you said flip a coin unless someone has some better info

 

Ima be running a true dual setup with a x-pipe dumped after the axle

 

use 2.5" exhaust then. screw the cats