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Old 10-29-2008, 01:34 PM   #26
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I'm running JRSC@9psi, DCRH & skunk2 70mm (2.75") megapower, works great, gain 7hp from my Tanabe 2.25" exhaust. And know a couple of blown guys runnin 3" custom exhausts with no problems. They say that's how they got the max hp's, runnin 3" but I'm skeptical about it so just went with 2.75".
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Old 11-28-2008, 11:00 AM   #27
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Erm not sure if I'm actually contributing anything and I'm sure loza or some other vets of the forum can probably say something more detailed with better descriptions of the physics, but my 2 cents would be the quote from Conrad, at the time quoting WDsonny in the description for the JRSC FAQ. I'm kinda lazy so I'll paraphrase: every 100hp requires 1" +. With that in mind, in theory wouldn't a 3" offer less restriction, resulting in more HP? I'm not saying it'll be all that noticeable and it may be a difference negligible enough that weather conditions or an uncontrollable variable may negate. All things equal, however, in theory it'd be better.

I remember Raz posted a long thread detailing his raz exhaust and he explained something contrary to that thought. Again paraphrasing I think he said that unlike NA S/C peeps can deal with a bit of blockage because S/C set ups don't need to scavenge that HP. His focus was albeit more focused on his header and ultimately noise reduction, but his point seems applicable. On a side note I kinda wanna ask why he didn't just get a huge ass resonator to negate sound instead of going with his exhaust? I thought you could control sound based on things like the resonator size and all that.

Nothing is really my thinking, just citing what other contributing board members post.
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Old 11-28-2008, 11:27 AM   #28
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I have a theory about this: Bigger diameter tubes are more critical to N-A applications than Roots-blown ones and I think that if you have a street-driven car, then there may be such thing as "too big".

The reason for that is one that we often overlook: While a 3" (or whatever diameter...) may be optimal for peak power, you and I are only in boost maybe 20% of the time. And for the remaining 80% of the time, your car is basically and N-A RSX and needs both exhaust scavenging and velocity.

The prime example of this is Wayne's car. His shorty header and 3" setup is great for WOT, but low-speed performance and fuel economy are inferior to the car with, say, a more vanilla header and exhaust.

This is the part I will never understand about many of us here: We tend to be sheep and blindly follow whatever the conventional wisdom about this or that. I am as guilty of that as anyone and have wasted several thousand dollars over the last four years buying headers or cat-backs that "everyone else" said would be great.

My point is that you need to keep things in context. If you have a strip-only car, then by all means, get that 3" exhaust and you will make plenty of power.

If you have a daily driver, ask yourself how many times a day you are boosting to max pressure versus the rest of the percentage that your car is in vacuum. I am typing from Starbucks right now and can tell you that in the 15 or so miles it took me to get here on the highway, I was in vacuum most of the time and what I would consider "light boost" the rest. Could a 3" straight-through exhaust make me a bit more power than the 2.5" setup I have now? Sure. Would I see any benefit from a 3" exhaust in my daily routine? No.

I am just saying that a max-power setup may not be what you want and you need to realize that what one guy says is the "only way to go" might actually hinder your performance. Just my opinions and best of luck to you all.
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Old 11-28-2008, 02:05 PM   #29
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^ i agree with this... the smaller the diameter the higher the velocity can stay at a lower rpm (of course can work as a restriction at higher rpm/higher power.) not only is it due to the scavenging effect of the low pressure (back) of the exhaust pulse attracting the high pressure side (front) of the following exhaust pulse... but turbulence at merges play a role as well. exhaust pulse really aren't just straight pulses moving through the exhaust, but at merges there is turbulence where part of the exhaust pulse makes a slight circular motion due to a vacuum effect right after the merge. this helps increase the speed of the pulses, and one of the contributing factors to a smaller diameter not hindering bottom end.
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Old 11-29-2011, 01:18 PM   #30
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^understood .. but what about a e-cut out .. header>2.5 test pipe>e-cut out .. the problem is how would this effect the superchargers performance or will it enhance it ,,,or is a full exhaust needed to keep enough pressure
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Old 11-29-2011, 01:23 PM   #31
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5" exhaust is needed.
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Old 11-29-2011, 01:23 PM   #32
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If the exhaust system is reasonably unrestrictive, then there is not a lot of point to the e-cutout.
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Old 11-29-2011, 03:35 PM   #33
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a guy in the uk forum just changed from 70mm skunk2 to a custom 3'' and gained 18hp. mase tuned it both times on the same rollers. 8psi i think.

http://www.civictype-r.co.uk/forum/v...?f=59&t=246186
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Old 11-29-2011, 06:19 PM   #34
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Old 11-29-2011, 06:38 PM   #35
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a guy in the uk forum just changed from 70mm skunk2 to a custom 3'' and gained 18hp. mase tuned it both times on the same rollers. 8psi i think.

http://www.civictype-r.co.uk/forum/v...?f=59&t=246186
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Old 11-29-2011, 08:51 PM   #36
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20hp seems like a lot for just another 5mm of exhaust diameter.
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Old 11-29-2011, 11:53 PM   #37
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Old 11-30-2011, 06:39 AM   #38
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20hp seems like a lot for just another 5mm of exhaust diameter.
don't know if the skunk2 is a true 70mm ID exhaust may be 66mm ID, if a true 76mm ID exhaust was fitted now its like 10mm difference which is a bit.
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Old 11-30-2011, 08:10 AM   #39
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