# good exhaust size?



## Tickwomp (May 27, 2003)

YES i did a search. didn't find NEthing on 2.25 vs 2.5 inch piping. ok so 2'' is good for a stockish motor, yet some say 2.25-2.5 is better for N/A. now i wanna know which is better. ive heard some say they lose power with 2.5 and such depending on mods. so far ive got a pacesetter monza catback...it was ok til the pipng started getting disconnected. this was after i put in my headers, so my question is should i get 2.5 inch piping? i plan on making my own custom exhaust set up since i think its cheaper...2.25 flows faster but does it flow enough? 

ive got 91 se-r cams, HS headers, intake, advanced timing, and i guess thats about it so far. i do plan on getting high comp pistons and ecu and stuff. not sure if 2.25 is sufficient or if 2.5 is too much...
thanks


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## niky (Jul 20, 2002)

it really does depend on your car... but if you are modifying it a lot, heck, go get the bigger pipe... you only need the smaller diameter so as not to lose bottom end, but if you're going all the way, just hit it.


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## bahearn (Jul 15, 2002)

You will NEVER lose power by going bigger O.D., you'll just take some torque from the mid-range and move it up higher into the rev range.

I have a suspision that all this talk about pipe size is irrelevant past the catalytic converter, but don't yet have the spare change to put my money where my mouth is. I feel 3" would be good even for N/A.


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## deception se-r (Jul 24, 2002)

3" would not be a good idea since this will make your car loose too much bottom end power. though you will probably gain more in the top end i dont think it will be enough to justify the lower end drop. 

my brothers 16v scirocco used to have 3" pipes and the thing would not get moving till the top of second gear. at that point it would fly. in the quarter he used to get walked by my sisters civic till 3rd when he would start to catch up but would still loose. he changed the exhaust to 2.5 and now he walks the civic in every gear. his upper end power is not as good as before but the drivability is much better, he no longer has to rev up to 1500 just so the car doesnt stall from lack of power to get it rolling.


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## bahearn (Jul 15, 2002)

Blah blah blah. Show me the dyno. When I can afford to, I'll show mine to prove it one way or the other.


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## Tickwomp (May 27, 2003)

im thinking about just keeping my 2.25 inch crap for now. the pacesetter piping is aluminized steel so its gotta be good for something. besides, its a hell of a lot cheaper than buying like 7 mandrel bends


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## deception se-r (Jul 24, 2002)

the nearest dyno is at least 1hr away and im not paying to get my brothers car dynoed when i have not even done mine yet. im not asking you to believe me if you dont want to. once you get your set up you will learn first hand. there is a reason you dont hear other people recomending an exhaust that big for a n/a applications. im not trying to get into an argument where neither of us has actual dynos to prove it, but one thing id like to know is if you have a full comprehension of how an exhaust works. if not i suggest a search here or on www.sr20deforums.com. there have been some very good explinations that may change your mind.


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## bahearn (Jul 15, 2002)

The reason you don't hear it is because "conventional wisdom" says otherwise. Well, "conventional wisdom" isn't a law of nature. I have run across a couple of items that leads me to believe "conventional wisdom" is improperly applied to this particular application.



> if you have a full comprehension of how an exhaust works. if not i suggest a search here or on www.sr20deforums.com


Funny, man. Funny. I think *YOU* should search sr20deforums for "slartibartfast" and see what I comprehend.


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## niky (Jul 20, 2002)

EDIT: double post!


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## niky (Jul 20, 2002)

can't we all just agree that the bigger the pipe, the higher up in the rev-range the power goes?

most guys don't like too big of a pipe because it moves that powerband higher than they would like... it all comes down to drivability... i personally hate it when a muffler shop gets the exhaust wrong on any of my cars, because it really hurts the drivability...

any pipe size increase beyond a moderate upsize WILL reduce low end power and INCREASE high-end power... at some point you will hit a pipe size wherein the losses in the lower revs will not increase hp in the upper range *before* redline... don't know if anyone has tried this, but who knows?

oh, by the way, this isn't taking into account the headers on the car... and you could just conceivably have the exhaust exit at the side of the car right after the headers....  ....then pipe size becomes totally irrelevant....


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## deception se-r (Jul 24, 2002)

^^^^ that is what im saying.

oh and i did search on sr20deforum.com and i found nothing really explaining your theory. all i found was a post where you say on some hotrod mag some time ago about them making power with exhaust sizes up to 3".


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## bahearn (Jul 15, 2002)

*NIKY*, I don't believe you can unequivically make that statement. That's the whole reason I'm involved with this discussion. I think header pipe sizing requirements are different than that after the collector. I think header sizing influences power curve shape and everything after the collecter just influences magnitude of power curve.


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## niky (Jul 20, 2002)

that could be true... but the total system still contributes to the backpressure and vacuum characteristics of the exhaust... still, you're right about one thing... most of the backpressure versus vacuum tuning occurs around the header and the muffler... the rest of the exhaust merely serves to get the air from point a to point b...

but then again, if you're going to run extreme pipe sizes, wouldn't it make just as much sense to chuck the pipe and go for a short exhaust?...

anyway, the gains made by going far-oversize are minimal once you've passed a certain point... what most people want to avoid with big pipe is turbulence (nope, i'm no aerospace engineer, but it's a valid point) at low to medium exhaust speeds... i guess it would be up to the end-user, in any case, how far he wants to go... and most end users stop at a certain size, and are happy with it...

no, 3 inches will probably not hurt, but it will likely not differ much from 2.5... the most difference i've noticed when redoing my exhaust system came with the headers, and i'm happy with having them.


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## bahearn (Jul 15, 2002)

> and most end users stop at a certain size, and are happy with it...


Trouble, they always ask baldly "What's best?" There is no "best", as I complained in a muffler thread. "Best" power demands biggest pipe. "Best" price demands something else. "Best" compromise, well, no one EVER asks that.


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## niky (Jul 20, 2002)

> _Originally posted by a bitter old man_
> 
> *"Best" compromise, well, no one EVER asks that.*


LOL! that's sad but true!


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## Tickwomp (May 27, 2003)

well i prefer not sitting at a light waiting for my car to rev b4 i move a few feet


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## PatScottAKA99XE (Apr 30, 2002)

bahearn said:


> *You will NEVER lose power by going bigger O.D., you'll just take some torque from the mid-range and move it up higher into the rev range.
> 
> I have a suspision that all this talk about pipe size is irrelevant past the catalytic converter, but don't yet have the spare change to put my money where my mouth is. I feel 3" would be good even for N/A. *


^^^I tend to lean this way also. I do share the cat-con suspision too. 

My other thought is that it may depend on what you want out of it. Do you want the highest peak hp or do you want the low end power? Me, I want the highest peak hp. Even though I have a N/A GA16DE I wouldnt be affraid to step from 2"(current) to 3" on that. I just dont see the reason people think you will lose hp by going bigger than what people say is the "best". I do belive however that going bigger than the "best" will move the power curve. Then again maybe Im wrong, correct me if I am.

bahearn, If you ever get the chance to do the testing you want I would love to hear the results.


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## Tickwomp (May 27, 2003)

in theory, it sounds like as u go bigger, it can move the power curve so far that it goes above revline. i guess you could consider that losing power. or ppl just think u lose it b/c you dont feel the pull u normally feel at a start


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## bahearn (Jul 15, 2002)

Please remember that we are talking about exhaust pipes, not headers.

Over certain size the exhaust pipe will effectively "disappear" and the engine will "think" the pipe ends at the catalytic converter. This will not affect where peak power occurs, rather how high the power will go. 

Header design will affect power band shape, so that's where one needs to carefully consider diameter.


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## Tickwomp (May 27, 2003)

heh, end it at the cat. too bad it sounds like crackling ass


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