GMade03

my trucks got a 4.8 with K&N intake factory tune, cats with true dual 2.25" pipes that lead into a magnaflow x-pipe and finish off with a pair of dumped spintech pro street mufflers... im doing my homework now on what pair of longtubes to go with but im wondering if i should up the pipe size from 2.25" to 2.5". im not planning on to much power for the truck (its my daily driver) goal is mid to high 300hp. im just not sure if i should go from a 3" collector reduced to a 2.25 is a good idea or not? can someone shead some light on this because it would sure be nice not have to go out and buy another pair of spintecs and x-pipe

GMade03

bumpty

outlawz2004

iTrader: (18)

I would stay with the 2.25. It is plenty with duals on the 4.8. If you really want to go to 2.5, they could always stretch the end of the spintechs to fit.Got any sound clips of the spintechs.

PathfinderJr

iTrader: (6)

Doug Thorley Tri-Y's have a 2.5" collector to facilitate easy necking down to a 2.25" pipe.

Are you keeping the cats? If so, you could always reduce to 2.5" from the 3" collector as you pipe to the cats, then do 2.25" after the cats so you can reuse your existing system.

What LT's are you looking at? The 4.8 (and even most 5.3's IMO) doesn't need the 1-3/4" primaries most LT's come with these days. The aforementioned Thorley Tri-Y's and the Hooker Super Comp's have 1-5/8" primaries which help boost the torque curve lower in the rev range. These smaller cube motors need all the help they can get to build usable torque.

JakeBrakeIH

iTrader: (22)

I just put OBX LTs on last week and I have a similar exhaust set up as you...I got 2.25 true dual to flows and I wanted to keep the same exhaust...I found a set of used headers that came with not a y pipe but 2 collectors so it went right on and got reducers and I just have it clamped for now because Im gonna put an H pipe in this week...

I say for the 4.8, 2.25 is plenty of pipe...my truck is a 5 speed and it REALLY helped low end torque...Id say from 1500 up is night and day...I do alot of stop and go driving and it made it much more enjoyable(or not so dreadful)...so I cant wait to put on the h pipe to see if that helps even more

GMade03

i plan on running no cats with the longtubes (possibly high-flow cats later on if i dont like the way it sounds) im still looking into which headers to go with the Hookers are nice and the Pacesetters are really affordable, to me almost seems like to affordable.. dougs are nice headers but is there a link to the Tri-Y's? all i could bring up was part number THY-309-C.

would stretching the ends of the x-pipe and mufflers to 2.5 be a safe thing to do? cant believe i didnt think about that

and heres an exhaust clip of it right now as is...

PathfinderJr

iTrader: (6)

I don't know of any sponsors that sell Doug Thorley headers, so in that case go to Summit and do a search for 310Y. It should come up with all the variations, ie ceramic, nickel chrome, etc. They're kinda pricey, but they're pretty nice headers. I've seen a couple guys around here run them.

GMade03

from what i see they only make those headers through the 2001 models would they work for an 03 like mine?

PathfinderJr

iTrader: (6)

yeah. The early models (through 01 or 02) had EGR stuff, but the General took that off the trucks later on. Those headers have the EGR bung, but all it requires is for you to get a plug/cap and bolt it on the bung. Easy as cake I'd imagine.

terravast4

iTrader: (25)

I think for the 4.8 and the 5.3 we need to stick with the small collector headers for the low end torque. we just don't have the cubic inches for the big tubes unless you want to sacrefice low end power.