say you have LTs with 3" collectors i dont see the point in over a 3" dual setup, if it was any bigger wouldnt the headers choke it down in the beginning

some scenario with 2.5" collectors and same way if it has a y-pipe instead of x-pipe

also i dont see the performacne benefit of a y-pipe to muffler to reverse y-pipe to tips

 

i have said for years and shown it on the dyno more than once that loss of low end with bigger exhaust is a myth. MAYBE extremly large exhaust and extremely low end like 1200rpm that idea would be true but thats just not an rpm most people care anything about. even at that rpm i would be suprized to see any loss.

open headers vs a typical cat back will show gains from 2000rpm up. significant gains up top, small gains down low. this is on a na engine.

on a boosted set up free flowing exhaust will show even more improvments.

a question i have is what is more free flowing a set of 3" pipes with a cross over or one 4". stuff like that. i can tell you true duels without a cross over will have a lot of resonation compared to the same set up with just a cross over added in.

 

The only reason that I think pipes larger then your collectors would be better is to help with the bends and to act more like it were open. I think y to muffler to y is just to get the look of duals. I have shorties, no cats, true dual back to dual flows and out the back sides. I gess if more flow the better a 4" system would work well if I can find a shop around that has it.

 

IMO the best exhaust for a N/A or streetable boost( supercharger, turbo requiers different setup) would be LTs w/3" collectors to off-road x-pipe to straight out 3" duals and some sort of highflow muffler like a magnaflow or a bullet

and just bigger tubing for bigger need

 

i didn't mean 5" would be good to use, just the measurement in theory. sorry about that.

i agree with parish (seen his dyno graphs), that's one of the reasons for my first post, I went from a huge (obviously over done) to a more reasonable exhaust and noticed no difference. This is also one of the reasons I also got rid of my electric cutout. It really wasn't helping any. And since it rattled like a f-er, I just got rid of it.

 

In your opinion then do you feel there is anything to gain in going from a true dual setup to one with a X pipe? Also if the exhaust is too loud ( resonation is hardly noticable on my setup) would adding in a X pipe help to quite the exhaust note some? Once I get my LT's on with off road mid pipes I am affaid mine will be quite loud, right now it is good.

 

an hpipe(xpipe even better) on my last truck made a huge differece in resonation and cackeling. it really toned things down and made for a more pleasant tone. i dont have any dyno numbers of my own with and without an x pipe but i have seen enough articles on them to say you should gain a couple of hp with one.

 

That is kinda what I was thinking, once I get the LT's on I thinking I am going to end up adding in a X pipe to tone it back down a tad.. Plus with no cats i thinking it may be a little bit crackly like you mentioned.. Especially on decel.

 

Your target power level is what determines optimal exhaust size. As far as velocity goes, a pair of long-tube headers are all you need no matter how oversized the rest of the system is realistically.

400-500HP, Single 3" or dual 2.5"
500-650HP, Single 3.5" or dual 3"
650-800HP, Single 4.0" or dual 3.5"
800-950HP, Single 4.5" or dual 4.0"
Over 950, Single 5" or dual 4.5"

A single pipe with the same internal cross section area as the combination of two smaller pipes flows better because there is less internal surface area for the exhaust to create friction with.

 

Here is what magnaflow thinks....http://www.magnaflow.com/wideopen/performdata.asp

PIPE DIAMETER AND PERFORMANCE
Use the guide below when calculating pipe size for custom exhaust work. Keep in mind that the goal is to improve exhaust flow. In most cases, just changing the restrictive OEM muffler and replacing it with the same size straight-through, Wide Open Performance MagnaFlow muffler will do this job.
To reduce additional backpressure, the OEM exhaust tubing can be replaced with madrel-bent tubing of the same size or one size up from the OEM. As a general rule, you can enlarge the pipe diameter of your OEM exhaust system by 1/4- to 1/2-inch to increase your horsepower. However, any additional increase in pipe diameter is likely to decrease your performance; specifically, low end torque.


Bigger is not always better.


Engine Size Horsepower Muffler Inlet / Outlet Size
Single Exhaust Dual Exhaust

150-200 CID 100 to 150 2" to 2-1/4" 2"
200-250 CID 100 to 200 2-1/4" to 2-1/2" 2" to 2-1/4"
250-300 CID 150 to 250 2-1/2" to 3" 2" to 2-1/2"
300-350 CID 200 to 350 2-1/2" to 3" 2-1/4" to 2-1/2"
350-400 CID 250 to 550 3" to 4" 2-1/2" to 3"