Exhaust question

Bulkybear

Bulkybear

Well-Known Member
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On my 9th Si, what size tubing is stock? I'm thinking about just taking out the silencer (resonator?) And chaning the muffler. I mainly just want it louder. Will probably add a cai or short ram intake and then flashpro in the distant future. My question is if I'm planning to stay NA and want just to do boltons and keep a daily driver would these give me a performance increase or would I HAVE to do a full exhaust and downpipe? My thinking is that keeping a little back pressure would be good for low end torque, so no 3 inch exhaust for me anyways. Any opinions?
 
I've seen two people claim they work for honda measure it. One said they measured 2.5", and another said they measured 2.25".
 
Hmm. I wonder which it is. And what power gains I could expect from resonator delete, muffler swap, and intake.
 
Here you go
http://math.about.com/library/blcirclecalculator.htm

Take a tape or string around the pipe. Measure that circumference. Input that value in circumference above and it'll spit out the diameter. The actual inner diameter will be slightly smaller than that value due to the pipe wall thickness.

I can't really say gains. I haven't seen anyone try what you're asking.
 
Ok ill try that later. I just read some about exhaust design and apparently the less back pressure the better. But you still want just enough back pressure to create a scavenging effect to increase exhaust gas velocity. The article makes me thing anything bigger than 2.5" on a 4 cylinder would actually lose power as while you lose nearly all restriction you also lose velocity too. So just theory here, but it seems like for staying NA I could get more power by doing a muffler swap and resonator delete, decreasing resistance while maintaining vacuum. So if the stock is 2.5" I might be better to stick with that. Anyone here have expertise on the subject?
 
Think of full-race, ultimate racing, etc running 3" on non-turbo setups. They are seeing gains there. Look at the people who've put those exhausts on so far. They aren't running turbo setups and praise their gains.
 
Are there any dyno charts on those? I wonder if its just a peak gain or if the entire powerband gets lifted. And also how they compare to a 2.5" aftermarket exhaust of similar quality.
 
Ok so our cars generally put out around 170 to the wheels. The only thing armo has that I wasn't on planning was a downpipe and he's putting out around 208 to the wheel. His chart also shows pretty much the same powerband as stock just more power if I'm reading it correctly. That sounds like a good plan. I'm horrible at forum research though, how does that compare with around the same mods just with a 3" exhaust instead of a axle back exhaust?
 
Downpipe is going to be the big gainer on the car. There are two catalytic converters it deletes. Rv6 and U-R downpipe/exhaust combos both show like 20hp gains to the wheels with just that. I'd wager 65-75% of the gains are all in the downpipe. There just aren't enough before/after dynos from users to say what each part produces.
 
I plan to get my car tuned with the stock exhaust and full race catless dp. Still deciding on AEM CAI, PRL SRI, or stock intake w/ K&N filter, though, before the tune.

I think most people on average have said they gained around 7 to 9 hp from a catback exhaust.
 
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