i just finished my stacks. i have a 4" downpipe to 4" flex pipe into the bed where i have 4" tubing into 5" stacks. instead of a split elbow type setup in the bed i just ran the 4" flex into the pipe in the bed in a t-type fashion. i will post pics soon. my question is that my tranny now seems reluctant to shift out of OD in the freeway unless i really step on it. a little more power down low around town so i know i have more back pressure than my old 4" straightpipe that dumped out under the cab. maybe its all in my head. my dad is sayin that because i have the T in the bed instead of a professional type split that would divert the gasses to each upright pipe that i am creating huge amounts of back pressure. any thoughts? do i need to buy a premade split and replace my T? i wouldnt think that 4" straight pipe into 5" stacks would create that much backpressure, but im sure that plain T i have in the bed isnt the best for flow. merry christmas BTW

 

Backpressure is more than pipe size. Think about how much more volume your exaust system now holds. All that has to get pushed out. I went from stacks to my pipe exiting right behind the passenger side door.

 

thats what type of exhaust i had b4 the stacks. any input from the guys who run high HP rigs? thanks. why did you take the stacks off? if i made my whole sack setup out of 5" would i gain anything? or should i ask, with it being made out of mostly 4" am i hurting performance at this point?

 

you've kind of got things backwards in your head, i don't want to argue with anyone but on a turbo charged engine less back pressure (AFTER) the turbo will create better spool up and bottom end, that said if you went to 5" with your setup,(stock turbo) I would go as far to say any single, as long as its not a 5" exit from the exhaust housing will not see any worthwhile gain in horsepower, where you get a real benefit from 5" is in a twin setup where there is alot more flow through your engine and therefore turbo's, 5" is necessitated.
Now on a third gen you will acutally loose power from going to a less restrictive exhaust, this is because the engine runs more efficient so it will build boost faster and the computer will defuel to keep the boost at managable levels.
Are you hurting the airflow with your TEE method? Yes.
Will you notice a difference in your setup? Probably not.

 

John, would you mind gettin us a pic of that new side pipe? I say it on a video but I would like to have something to go by cause I am thinkin of runnin the same set up. What differance(s) did you notice going form stacks to the current set up? Louder, quieter? Better spoolup, worse spoolup? Etc.

 

The pipe diameter is not the problem.... We make over 830 RWHP out of a 4" exhaust with a muffler!

Doug

 

if you are in doubt about the tee setup. Remove the tee and stacks and just run the pipe into the bed and dump out. go for a test drive and see if it makes a difference.

 

Rocket, I agree with jetpilot. Keep the exhaust as short, straight and simple as possible, I have mine exit straight out the side with an mbrp cool duals muffler with twin tips. It exits at the up hump in the frame just before the rear wheels. I'm still 3.5 into 4 into muffler with two down turns. One 90 degree bend at the muffler and out. The stock muffler with all those bends and the length of the long bed is restrictive. I'd only get 5 inches if that was the outlet size of the big turbo on a set of twins. Im thinking of putting in a 27" 4" straight through to make it more stealth but I love the sound right now.
You are definitely loosing performance if you don't use a box with boost fueling. ks

 

well then i shouldnt be losing any performance then. i was aware that a 5" was only really necesary on very high HP rigs. i was reading another thread and am starting to think i may need to tighten up my tranny bands. 36k and iv never done it. for those of you with your stack setup made entirely out of 5" does it sound any different then a 4" into 5" like i have? its got a nasty drone at about 1600rpms. thanks for all the info. i'm on disability now so i have all the time in the world to mess with the truck, just no money

 

One other thing to consider, the inside of flex pipe is not smooth. The ribbed surface causes more turbulence, i/e backpressure. Use very short lengths of flex, only to allow flexing of frame.

 

heres some pics...
[IMG] [/IMG]

theres what it looks like in the bed. you can see how i did the T setup