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2.5 inch exhaust for SR20DET

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I'm putting on a 2.5 inch exhaust on my boosted S13. All it has is a front mount and boost controller.

 

I'll be running a 2.5 inch exhaust with no resonator and I want to know if it's too small for my car.

 

I'll be upgrading soon but I want to know if it's okay performance wise.

 

Thanks.

 

Ps my dump pipe is 3 inch.

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you should go for 3inch and use a muffler. sr's sound shit with straight pipes, and 2.5inch will likely be too restrictive beyond 200-ish kws (it was for me)

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a consideration: would the drop in diameter increase response for those not aiming above ~200kw?

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Well I have around 160kw.

 

Should be okay? It's also not a straight pipe lol, I'll have one of those oval kakimoto mufflers

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2.5 inch is pretty restrictive for a turbo. Not going to hurt anything, just restrictive.

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Would I feel a loss of power from a 3 inch? Noticeable? I'm running around 12-13 psi

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with a 2.5inch you would feel increased torque and response in the lower rev range. this would die off dramatically in the higher rev range. i would stick to a 3inch all the way through.

Edited by fyjosh

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Oh ok I see, well it's a free exhaust so I was just seeing if it's worth the effort putting on. I run it until I get a proper 3 inch then ;)

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Would you consider doing the front pipe (the first bend) in 3" then making a ~300mm long taper from 3" to 2.5"? That'll give the gas a bit more time to cool and straighten before it has to reduce, giving you more power potential.

 

Why 2.5" with no middle muffler? Generally people run 2.5" to get it quieter but not running a middle muffler kinda defeats the purpose IMO.

Edited by bradsm87

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FMIC

stock ECU

stock boost

stock cat? looks stock

 

had a 2.5 cat back, only had muffler on the end, car stopped pulling after 5500rpm ish? was a nugget

now i has 3inch cat back, with resonator and muffler, car pulls to red line

 

defiantly allowed the engine to flow a whole lot better and happier

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So you didn't change the cat? That sounds very strange to be honest. 2.5" has a LOT more area than the stock exhaust and generally won't hold a setup back below 200kw.

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tbh im not sure if the cat is a stock one, but it sure does look stock now if it isn't. old, bronze in colour, just nasty. but the point is i swapped the cat back to a larger diameter one and saw gains everywhere. Maybe a little loss down low? but its so little its not worth mentioning.

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tbh im not sure if the cat is a stock one, but it sure does look stock now if it isn't. old, bronze in colour, just nasty. but the point is i swapped the cat back to a larger diameter one and saw gains everywhere. Maybe a little loss down low? but its so little its not worth mentioning.

 

Did the 2.5" system have a straight through muffler that U could see straight through? If not, could've been the muffler. Was it mandrel bent or crush bent?

 

2.5" exhaust is completely fine 200kW+ BUT ONLY if you're running an external gate dumping to atmosphere hehe... GGGAAATTEEEEE :D

 

That's what I'm running. Loving it.

Edited by bradsm87

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you couldn't see straight through the muffler, there was a S bend in it or something, and as for the pipe bends it was non-mandrel.. its was just a cheap exhaust

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I reckon the new exhaust not having the above issues would be the main reason for the improvement rather than the diameter change.

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2.5inch will be totally fine. Most of the evidence pro-3inch comes from comparisons between stock and 3inch. There are plenty of cars running higher power figures with more exhaust restriction (look at other cars).

 

I'd say if you take a good 2inch and a good 3inch at sub-200rwkw (or even 250 perhaps) you'll see no difference in performance.

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Thanks for all the info guys!

 

Would it be wise remove my cat too? At the moment I have a high flow one but I got a hollowed out one lying here

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Besides the good guy environmental conversationist in me, it's just another restriction?

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Generally, a hollowed out cat will perform same or worse than a high flow cat due to the sudden change up then back down in diameter. A straight pipe, however, performs best at the expense of emissions.

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i found no differences in performance between decat, normal cat and high flow cat... the turbo is the restriction... everything past it doesn't make -too- much of a difference.

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2.5inch will be totally fine. Most of the evidence pro-3inch comes from comparisons between stock and 3inch. There are plenty of cars running higher power figures with more exhaust restriction (look at other cars).

 

I'd say if you take a good 2inch and a good 3inch at sub-200rwkw (or even 250 perhaps) you'll see no difference in performance.

 

this.

and alot of people stop modifying at 200 - 250kw anyway, because beyond that, it starts to cost real coin, with all the supporting mods etc to do shit properly.

if youre one of those people (alot of us are) who will want more and more power and have the cash, go a big as you can. exhausts are fkin shit to work on and you dont want to be changing them often.

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i found no differences in performance between decat, normal cat and high flow cat... the turbo is the restriction... everything past it doesn't make -too- much of a difference.

 

that really only apply's to people running fairly standard setups

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i found no differences in performance between decat, normal cat and high flow cat... the turbo is the restriction... everything past it doesn't make -too- much of a difference.

 

that really only apply's to people running fairly standard setups

 

but kemp

if you know youre shooting for 400kw, youre pretty thick if youre putting a 2inch system on.

like i said, if youre getting around with a t28 and 14psi, who gives a shit what size your exhaust is, going to make stuff all difference.

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i found no differences in performance between decat, normal cat and high flow cat... the turbo is the restriction... everything past it doesn't make -too- much of a difference.

 

that really only apply's to people running fairly standard setups

 

but kemp

if you know youre shooting for 400kw, youre pretty thick if youre putting a 2inch system on.

like i said, if youre getting around with a t28 and 14psi, who gives a shit what size your exhaust is, going to make stuff all difference.

 

i agree but i would still throw a bolt on 3 inch kit rather than a 2.5 but thats me...

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Maybe ive matured a bit but these days I have a lot more fun with a well balanced exhaust note, on the quiet side. My 1J pushes around 250 at the wheels right now, soon to be creeping on 300... I want it to be quieter. I have a 3inch system and it started off as a total straight pipe (insane sound), and I just been adding more and more mufflers to it. I want it to be as quiet as possible. Yes it's a street car, sorta.

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Maybe ive matured a bit but these days I have a lot more fun with a well balanced exhaust note, on the quiet side. My 1J pushes around 250 at the wheels right now, soon to be creeping on 300... I want it to be quieter. I have a 3inch system and it started off as a total straight pipe (insane sound), and I just been adding more and more mufflers to it. I want it to be as quiet as possible. Yes it's a street car, sorta.

yeah im the same i want my car quiet but its hard to make power while keeping the car quiet, love having a varex

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No damnit! It's not hard at all! You don't see the new Porsches struggling to make power, do you :P

 

Mufflers and such add sweet f**k all restriction to an exhaust - relative to the turbo. The flow capacity of a 3inch pipe is insane, even with as many bends as shit as you want in there.... and don't get me started on ridiculously sized intakes lol

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