Im curious about if there is any benifit to going with say a 3" exhaust after the donpipe on my turbo. From what ive read turbos like no restrictions but if the largest downpipe i can run is 2.5" will it only flow as good as 2.5"?
I know it is like that with n/a so final question..being tat im running a 2.5" downpipe..should i go with a 3" or 2.5" exhaust after the downpipe? many thanks..phil
well it will all help if you can do it might as well
<img src="http://img46.imageshack.us/img46/227/cave10wf.gif" />
2.5" DP on my car (standard T3/T4 turbo) and a 3" exhaust after the engine cradle. Eventualy when I upgrade the turbo to something better I will make a 3" DP for the car. Its a 2.4L BTW.
I would go 3 inch all the way IF you could, but if its easier or more convient <sp> to go 2.5 to 3.0 then do what you have to do. I did the same just recently (but on a smaller scale) with 2 1/4 down pipe that opens up to 2 1/2 inch all that way back, including taking out the cat. As long as your not goin big to small, usually the down pipe is only about what...2 feet long of pipe....so cant be too much restriction.
To answer your question, yes there is a benefit. Once the exhaust gasses transition to the 3", they will expand and cause rapid acceleration, blah blah blah it will be better than keeping it 2.5"
Fabricator X
Philly D wrote:From what ive read turbos like no restrictions but if the largest downpipe i can run is 2.5" will it only flow as good as 2.5"?
It's the other way around. Starting from the back of the exhaust, it'll only flow as well as the smallest section. So if you had a 3" downpipe going into a 2.5" cat-back, the whole thing will only flow as well as a full 2.5" exhaust. Opening up from 2.5" downpipe to 3" will cause less restriction than all 2.5" piping. Turbo + less exhaust restriction = good.
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450WHP Turbo Ecotec swap in the works...
^awnser i was looking for..thank you..
NRG wrote:To answer your question, yes there is a benefit. Once the exhaust gasses transition to the 3", they will expand and cause rapid acceleration, blah blah blah it will be better than keeping it 2.5"
that isnt true , the gases slow down due to having to fill a larger air space
best is to run the 3" as close as you can get to the turbo , if you want the higher peak HP #'s
a full 2 1/2" isnt gonna hurt you , if your gonna run moderate boost levels , and rarely race it
well im running the saab setup..and bradoson only makes a 2.5" down pipe...but from there back id run3"
he ran a full 2 1/2" exhaust , and made over 200(i forget the exact #s)whp and over 270wtq , and ran high 13's
youd prob pick up some hp , and drop the tq down some going 3" , based from his #'s
would be interesting to see #'s from the saab set up with near full 3" system
ill be putting numbers up as soon as i get it all done....3" exhaust, 2.5" charge pipes..saab intake, among other fun stuff.
[quote=97cavie24ls(™)]youd prob pick up some hp , and drop the tq down some going 3" , based from his #'s
This is a turbo car we're talking about. You're not shooting for small piping with high exhaust velocity to maintain torque. Having larger piping will help make more power, but will also allow the turbo to spool quicker and will make more torque than the small piping and probably earlier in the RPM band.
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450WHP Turbo Ecotec swap in the works...
[quote=97cavie24ls(™)]
NRG wrote:To answer your question, yes there is a benefit. Once the exhaust gasses transition to the 3", they will expand and cause rapid acceleration, blah blah blah it will be better than keeping it 2.5"
that isnt true , the gases slow down due to having to fill a larger air space
best is to run the 3" as close as you can get to the turbo , if you want the higher peak HP #'s
a full 2 1/2" isnt gonna hurt you , if your gonna run moderate boost levels , and rarely race it
not necessarily in a boosted scenario like this. Whatever the specific situation, in any test I have done/seen, torque was gained when switching from a 2.5" exhaust to a 3" exhaust, on a 2.5" downpipe
Jimmy
Action RaceFab
480-862-2209
ActionRaceFab@Gmail.com
I have a 3" downpipe, and I can tell you when I take my cutoff plate off, it bogs like hell before it hits boost, Im pretty sure there is lost torque from it.
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Mitsu TD06-20g |3" Downpipe w/ Cutout | 61mm Bored TB |
HP Tuners | Innovate WB02 | Spec Stage 3 | TurboTech Upper | Full Addco Sways | Sportlines & Yellows |
Factually, 2.5" will suffice up to 400whp or so before it actually begins to sway numbers. I wouldn't even bother unless you've just got money throw around.
Blew it up, build numbers coming soon
NRG wrote:[quote=97cavie24ls(™)]NRG wrote:To answer your question, yes there is a benefit. Once the exhaust gasses transition to the 3", they will expand and cause rapid acceleration, blah blah blah it will be better than keeping it 2.5"
that isnt true , the gases slow down due to having to fill a larger air space
best is to run the 3" as close as you can get to the turbo , if you want the higher peak HP #'s
a full 2 1/2" isnt gonna hurt you , if your gonna run moderate boost levels , and rarely race it
not necessarily in a boosted scenario like this. Whatever the specific situation, in any test I have done/seen, torque was gained when switching from a 2.5" exhaust to a 3" exhaust, on a 2.5" downpipe
The gain only applies in the case of the turbo, because you're reducing any points of high pressure in the REST of the exhaust (ie bends). However, it still stands that you're slowing down your exhaust gases. It's bernoulli's principal; a greater cross sectional area will result in lower exhaust velocities.
" To study and not think is a waste. To think and not study is dangerous. "
Well its not i have money to hrow around..lol..i have a 2.25" on there now....im going to be upgrading..
Unless your planning on making HUGE power the 2.5 will be fine but for the record the bigger the down pipe the better. Turbos do not use scavenging in the exhaust like n/a cars do so back pressure is not a problem. In an ideal set up the down pipe would just be a cone, kinda like a velocity stack... but we all know that would get the wrong type of attention!
this case was talking about a boosted scenario, thus I wouldn't use data based on the volumetric efficiency of a N/A engine
Jimmy
Action RaceFab
480-862-2209
ActionRaceFab@Gmail.com
wow..this got confusing fast...
In my opinion, anything a larger diameter than the exhaust outlet on the turbocharger would be sufficient. On my 16G, the exhaust outlet is maybe 2 inches, and I'm running a 2.25" downpipe to 2.5" resonator and cat-back, and trapping 13's in the 1/4 on slippery street tires.
Currently #4 in Ecotec Forced Induction horsepower ratings. 505.8 WHP 414WTQ!!!
Currently 3rd quickest Ecotec on the .org - 10.949 @ 131.50 MPH!!!
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Factually, 2.5" will suffice up to 400whp or so before it actually begins to sway numbers. I wouldn't even bother unless you've just got money throw around.
i agree.... 3" for the most part isnt going to make any difference over 2.5" until you start really pushing out some power....
we have 2.5" all the way back on our cobalt ss/sc and its running low 13's (this was on a slipping clutch - we havent run it since we put in the stage 4 clutch and light flywheel, also on horrible tires.) this car is now capable of 12's if we had the money to put drag radials on it and it still has the stock 2.5" piping. everyone we know with the cobalt ss/sc has upgraded their exhausts to 2.5-3" "aftermarket" exhausts (yes - 800$ + for the catbacks) and they area running either the close to the same but mostly worse than his times (similar modded ones). i mean that could be any number of reasons but for the most part it goes to show it doesn't make a huge difference until your pushing out
big amounts of power. if anything in some cases it can hurt you to go too big..
correct points made here. key thing to look at isn't necessarily horsepower, but cfm. if were running a low boost setup, less cfm is being pushed, thus does NOT require a larger than 2.5" downpipe to be used!
Jimmy
Action RaceFab
480-862-2209
ActionRaceFab@Gmail.com
