Exhaust Question, matching dp/piping/muffler size Options

[elvasoshexai]

ok... i have some questions that sounds really dumb... but i just wanted some opinions

at first.. i was planning on doing 2.5" exhaust from turbo back... cause 3" seemed unnecessary for my goals (my goal is about 200-220whp...) and i thought that using the same size piping all the way back would be better too since maybe the gases would flow smoother?.?.?.

1. then i was looking around and 3" DPs basically cost the same as a 2.5" DP... and it seems that from tests done by KOR and Berk... with a 3" dp you get faster spool and a couple more horses if all you replace is ur 2.5" DP w/ a 3" DP and nothing else...however... all these tests were for 3sgtes... i'm not sure if our 5sfe's would benefit from one since we are already pushing our engines near the edge

2. i also wanted a magnaflow muffler... but they only have 2 models that i liked... and neither had a 2.5" inlet... one had 3" inlet w/ 3" internal core and the other is a 2.25" inlet w/ 2.5" internal core...

i dunno if my thinking is flawed.. but like... if u go from 3"DP to 2.5" piping.. ur pushing more air into a smaller area and so... it would hv mroe restrictions.. then ur goign from 2.5" back to 3" but now the gases are coming out from a smaller opening and so it's not as smooth... so......... if i am using 2.5" piping from after DP to before Muffler... i was just wondering which would be a better idea:

-2.5" or 3" DP? (especially those with 5sfte's w/ a 3".. would u do it again or just use 2.5")
and
-weld a muffler w/ 3" inlet and 3" internal core or remove 2.25" inlet and weld to muffler so it'sstraight 2.5" all the way bacK?

i would think the muffler part doesn't make much difference at all... but well.. couldn't find an answer on it...

This post has been edited by elvasoshexai: Oct 6, 2006 - 2:45 PM

[playr158]

3" straight back any deduction in pipe diameter is considered a bottle neck and bad for performance

[lagos]

what do you want to do this on? 5sfTe or a 3sgte?

a full 3in exhaust on a 5sfTe might not be the best thing to get, because you get a lot of boost creep with an exhaust that size.

[elvasoshexai]

what do you want to do this on? 5sfTe or a 3sgte?

a full 3in exhaust on a 5sfTe might not be the best thing to get, because you get a lot of boost creep with an exhaust that size.

it's for a 5sfte... was planning 2.5" all the way... but then was wonderin about the DP and muffler

[beno]

a full 3in exhaust on a 5sfTe might not be the best thing to get, because you get a lot of boost creep with an exhaust that size

would a bigger wategate not fix boost creep?

[JDM_ST205_WRC]

a full 3in exhaust on a 5sfTe might not be the best thing to get, because you get a lot of boost creep with an exhaust that size

would a bigger wategate not fix boost creep?

Not necessarily, although the wastegate in most situations is the normal fix or culprit, boost creep can be caused by back pressure issues like having a cr@p flowing exhaust, too bigger exhaust, cr@p wastegate flow into the main exhaust, etc.

i dunno if my thinking is flawed.. but like... if u go from 3"DP to 2.5" piping.. ur pushing more air into a smaller area and so... it would hv mroe restrictions.. then ur goign from 2.5" back to 3" but now the gases are coming out from a smaller opening and so it's not as smooth... so......... if i am using 2.5" piping from after DP to before Muffler... i was just wondering which would be a better idea:

I run a 3” DP to a 2.5” flexi section then back to a full 3” system, this puts a small restriction in the system which resolves my temporary issue with boost creep by regulating the back pressure.
Most of us in the UK run our systems like that (3S-GTE) there are no issues with running this type of set-up.
Most peeps are not running enough Bhp to warrant a 3” full system, on a 3S-GTE I think the figure is near on 360 horses before the 2.5” becomes too restrictive or an issue.

Besides if at a later date you find the 2.5” is too restrictive pull it out & swap it with a 3”… jobs a goodun

[presure2]

if i were doing it again, i would have went with a 2.5" turbo back setup..
IMO the 5sfte dont flow enough up top to warrant the 3"
if your shooting for all out performance, then yea, 3" would prolly be the way to go..
but for most moderate 5sfte setups, 2.5" will be more than adequate.

[x_itchy_b_x]

I enjoyed my 2.5" on the 5sfte with matching downpipe, The FE head limits alot of flow thats where 3sgte makes the power and flow. well any motor for that matter is the head. if you plan on running aftermarket camshafts/valves that allow more air flow then you should go 3" but like manny said. 2.5" is adequate for a moderate 5sfte setup.

[elvasoshexai]

this is the issue i have right now... i only see one 2.5" DP available... and every other DP out there is 3"... but they are all within $10 of each other or so... so it seems like... if for $10 more i can get 10whp more... it would be worth it...

but then i'm also considering just buying a dp + cutout and saving like $700 on a full exhaust...

i really suck @ making decisions =/