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Turbo Exhaust Piping Size??????

6506 Views 15 Replies 11 Participants Last post by  myflysi
There is a very good chance I am going turbo this summer and am confused as to what exhaust size to go with. I have heard that 3" is obnoxiously loud. I do not want to buy another cat back system, sold my EVO to Pete already. Should I go with a high flow cat and a custom 2.5" piping? Thanks, Jeff
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If you get a high flow cat, and 2.5inch custom pipe with out a resonator, your car will be loud...Trust me!!! I had that same setup on my 95 EX.

Why don't you just buy a cat back that has a large diameter pipe? In the end it really isn't that much more money, and imo I would rather spend the extra money to be sure everything is as perfect as it could be.
i would go all out and get 3in piping with Apex n1 muffler :)
I would go with 2.5-6"....3 is too big unless your making upwards of 350whp...just make sure you get a dp to match as well as a cat with the same diameter...the turbo will quiet the exhaust down too
Until you are certain that you'll eventually be boosted, don't buy anything w/ a diameter larger than 2.5". Of course, for our cars, this isn't an easy thing to do since most companies use 60mm piping. If you intend not to remove your air conditioner compressor, your downpipe will likely be no bigger than 2.5" in diameter. If that is the case, at no point in your exhaust system will you want the diameter to be smaller than that. Also, if you are to have the system custom made, it would be to your benefit to have it mandrel bent.

Thermal Research and Development makes an exhaust specifically for forced induction Acura's and Honda's. Click here for more info., part numbers or to contact TR&D.

No matter what diameter you choose, if you decide the exhaust note is too loud, there is a relatively easy and inexpensive remedy. Purchase a good ol' glass pack (I like the Cherry Bombs personally.) from your local automotive parts store. They can be had in diameters of 2.5", 2.75", and 3" and typically cost no more than 20 USD's. Next, weld it in backwards on the B-pipe, the section between the catalytic converter and the muffler. You don't have to put in on backwards but I find that it does not disrupt exhaust flow and also quiets things down a bit more than positioning it the "correct" way.

I HTH and if you have any more questions, don't hesitate to ask. :)
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If you are absolutely sure you are going turbo 3" is the thing tohave. Not only less back pressure but spool up time is better with a bigger exhaust. Once the caris turboed the exhaust will quiet down considerably.
madtownhonda said:
...3 is too big unless your making upwards of 350whp...
That is incorrect for the same reason that the turbo quiets down the exhaust. The turbine creates enough back pressure that only a downpipe is needed. The rest of the exhaust is there for emissions and to make sure the tailpipe clears the rear bumper cover.

The turbo acts as about 1/3 of a muffler relative to exhaust noise and as about an entire exhaust system relative to back pressure.
OK....lets say you have an 2.5" exhaust on an NA will be loud because there is little to no backpressure...when you add a turbo, exhaust will be quieter because there is more backpressure...the more backpressure you have, the less sound will come out.

The exhaust does more than just emissions stuff....when the high pressure waves travel down the exhaust, some reflect back as a low pressure waves....low pressure waves help create the scavenging effects that draw the exhaust out of the cylinder...don't want that spent exhaust to dilute the fresh intake charge....if the turbine is creating to much backpressure, then it isn't big enough....our small engines make power higher in the rpm range so there is no need for such a small turbine inducer unless your trying to reduce turbo lag

I'm not a very turbo knowledgable guy, but that is my take on it.
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Go 3", turbos do not like restriction, make sure you have a good wastegate and manifold because with 3" you may get some boost creep. 3" will help your spool up time also. If you plan on staying with low boost, then you are obviously not looking for all out power, just a little something extra, which in that case I say get what ever damn exhaust you want.
Jeff you changin your mind again?;) J/k. Agree with CleanSi, I would go with 3".
i run 3" straight pipe (no cat) to 3" thermal exhaust...........its plenty loud, but it will quiet down if you need it to. personally id have nothing but 3"

if you plan on going with the GReddy kit, then you can prolly get away with a smaller diamter since its a smaller turbo. but just like clean said, larger the better (to some degree) for turbo applications. hope to see you on the dark side hehhe.......
3" is too big....when you start to push 300whp start to look into 3" piping.

an exhaust is an exhaust, just because a company deems it a turbo exhaust, does not mean that it's the best exhaust for a turboed car.

2.65" or so would be good for a boosted start to go bigger, the exhaust gas moves slower...when it moves slower, it cools off and thus becomes denser, heavier air.....this is not a hard concept to understand...which would you rather push to a gas station, an f350 or a metro....get it, good....not only that, but like I said before...the exhaust gas comes out in pulses...the head of the pulse is a high pressure, the tail end is a low pressure....high pressure goes to low pressure, so the head of the next pulse will be sucked out by the tail end of the previous pulse....if you go to big, the pulses don't line up (higher entropy) and the sucking doesn't quite, I like it when sucking goes good, I'm sure most of you can appreciate a good sucking too:D

it's hard to figure out the ideal exhaust diameter...a lot of it has to do with design, bents, dents, etc.
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Actualy you realy cant go too big with turbo piping, but sound is a big concern. Even when I ran no muffler on my car (Accedent) it wasn't too loud, just a little anoying. So I would go with 2.5" to 3", its realy up to you. Apex-i makes a universal 3" muffler that would work good. And a test pipe is the only way to go, most turbo systems (Except Greedy) are'nt SMOG legal anyways, so you might as well just chuck the cat.
I'm getting the carb legal greddy system. I don't want a very loud car(exhaust wise). I'd like my car to only be loud when I'm on it in turbo range. I want it to be quiet when I am rolling up at 2K rpm's, ya know?? I do not want police attention anymore. Still baffled...
Just go with a good universal muffler (Ex. Apex-i, Greedy, HKS, Etc...) and get 2.5" piping. It shouldn't be too loud, especialy since you are going to have a turbo blocking a lot of sound. And at the track just have the exaust going right out of the down pipe. I'm about to cry thinking of my once destended Turbo Si. But, that was last september and some guy in Lancaster is about to get sued for 2 grand. What kind of times do Greedy Si's normaly run? I'm going to put a B20 block in my car and I all ready have a 80 shot. So I think I could easly out run Greedy Si's.
LAblue said:
i would go all out and get 3in piping with Apex n1 muffler :)
3 inch piping isnt going all out, bigger isnt ALWAYS better, there is such a thing as over kill and a serious loss of needed backpressure (helps low end ballz)- get the n1 catback exhaust system- ive yet to see a better exhaust on the market for the si. good luck
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