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exhaust piping diameter??

 
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Old 04-20-2010, 12:30 PM
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exhaust piping diameter??

I keep hearing mixed things about getting 2.5" piping vs 3". can anyone clarify wat yields the best results on a h22a1 with basic bolt on mods. I was to get it tuned after i get a hytech replica and new exhaust system. people are telling me that the h22 likes 3" piping, then others say its too big, 2.5 max. so im confused on wat to get. i want it done right the first time for my tune.
thanks in advance
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Old 04-20-2010, 04:53 PM
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Re: exhaust piping diameter??

Go 2.5 inch for NA and 3 inch for turbo. Simple. Going 3 inch with basic boltons will kill low end torque and probably midrange. When the piping is too big the velocity of the exhaust gas is reduced and thus scavenging is reduced, long story short, torque will suffer in an stock NA engine with boltons and 3 inch exhaust piping.
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Old 04-20-2010, 06:08 PM
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Re: exhaust piping diameter??

Quote:
Originally Posted by MilanoH22ALude View Post
Go 2.5 inch for NA and 3 inch for turbo. Simple. Going 3 inch with basic boltons will kill low end torque and probably midrange. When the piping is too big the velocity of the exhaust gas is reduced and thus scavenging is reduced, long story short, torque will suffer in an stock NA engine with boltons and 3 inch exhaust piping.


i like your train of thought....
but its wrong


http://bbmoto.net/wiki/index.php?ExhaustTheory
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Old 04-20-2010, 08:17 PM
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Re: exhaust piping diameter??

Quote:
Originally Posted by twokexlv6coupe View Post
i like your train of thought....
but its wrong


http://bbmoto.net/wiki/index.php?ExhaustTheory
something like this is just wat i was looking for. thanks a lot!!
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Old 04-20-2010, 11:20 PM
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Re: exhaust piping diameter??

ohh glad i read that. i did not know that. now i will raise my car big time and put a 6" EXHAUST
BRAHHHHHHHHHHAPPPP
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Old 04-21-2010, 02:15 AM
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Re: exhaust piping diameter??

Quote:
Originally Posted by MilanoH22ALude View Post
Go 2.5 inch for NA and 3 inch for turbo. Simple. Going 3 inch with basic boltons will kill low end torque and probably midrange. When the piping is too big the velocity of the exhaust gas is reduced and thus scavenging is reduced, long story short, torque will suffer in an stock NA engine with boltons and 3 inch exhaust piping.
wrong
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Old 04-22-2010, 12:41 PM
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Re: exhaust piping diameter??

ok im going with 3" mandrel bent piping. the collector on the header is 2.5". a exhaust shop will be able to hook up a 3" cat to it right
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Old 04-22-2010, 08:35 PM
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Re: exhaust piping diameter??

Quote:
Originally Posted by twokexlv6coupe View Post
i like your train of thought....
but its wrong


http://bbmoto.net/wiki/index.php?ExhaustTheory
Quote:
Originally Posted by 2.2Lude View Post
wrong
Fair enough, it’s your call, 2.2lude, care to elaborate. To me the key thing is “best results on an h22a1 with basic bolt on mods”. Guess this happens when things are simplified without a detailed explanation in brackets after it....

Indeed a 3inch exhaust, CAT back, will yield more power on an H22A in the upper RPM ranges (3-8k RPM). The one thing that is undesirable in this setup is noise. Going 3inch greatly increases the noise, and as we all know, 4 cylinders have a rather annoying tone when running open header etc. Guess that’s were personal interpretations come about (with regards to the question asked); to me the BEST results on an H22A with basic bolt-ons will be through the use of a 2.5inch CAT back exhaust. Highest horse power/torque, maybe not, but best in the sense of a reasonable power gain for little “irritation” on a daily driven Prelude. If kkp5006 is going to use the car for drag racing/track racing then 3inch is the way to go (he will have a helmet on so no noise issues, unless the track has noise restrictions, of which most do nowadays, at least where I live), 3inch yields best mid to top-end power gains on a 2.2 H22A (not on B16A’s or B18C’s, for the record (the detail in brackets I mentioned before, haha)). If he is, like most rational people, going to use the car on the street as a daily driven then I would not recommend a 3inch exhaust as the BEST option.

In your link twokexlv6coupe, they are were testing a skunk2 exhaust and a 3" exhaust on an h22 motor that is otherwise stock other than minor bolt ons and tuning (for the skunk exhaust). Some good findings obtained, and puts an end to those who say 3inch exhausts only loose power on near stock H22A’s (I recall a few threads on Honda-tech over the last 6 years or so).

What I would highlight is the fact that they mentioned:

Quote 1:“Big engines need big exhaust in order to allow proper flow”.

Quote 2:“The last merge is typically at the end of the header before going through the cat-back so my interpretation of this statement is that the bigger you go, the more power you will make.”

Quote 3:”After the last collector, there is nothing left to pull the exhaust.”

Quote 1 has truth in it in that a bigger engine displacement will result in more exhaust being produced and thus an increase in exhaust diameter will be needed as displacement increases, obvious really.

Quote2 has a slight flaw, “my interpretation of this statement is that the bigger you go, the more power you will make”. I take it scavenging is not well understood if a statement like this is made. Economies of scale, going too large will eventually reduce power. WHY you ask? Helmholtz resonance (check Wikipedia for a basic definition). Without going into much physics and making a huge post huger, exhaust gas pulses being forced into a confined space like the collector etc will have inertia/momentum; this is coupled with a high pressure and low pressure section of this flowing gas. As the gas moves, the low pressure area is created behind the gas, almost like a vacuum effect (air likes to equalize its pressure). The key property of the gas that generates this vacuum like effect is the momentum of the gas. The end result of this momentum is that it is able to drag/pull gasses moving behind it (scavenging effect). This effect is really important at low RPM in that this pulling effect is able to pull exhaust gasses out of the cylinders, and providing there is valve overlap, it can also pull in the intake charge, which will increase low rpm torque.

So now you ask, what does this have to do with a 3inch exhaust on a H22A? Well, the velocity of this exhaust gas is the key factor that determines the ability of this pulling effect (scavenging) to create more power. A smaller diameter pipe will increase the velocity of the gas and thus enable a greater ability to remove gas from the exhaust through scavenging. Naturally the size of the pipe will also put a restriction on the volume of gas it can flow as rpm increases. At low rpm (3k RPM and below) you would ideally want a small diameter exhaust (say 2inch on an H22A), but once you get to 7kRPM the amount of exhaust gas produced would have dramatically increased, hence a bigger diameter pipe will prevent the exhaust gas from causing back pressure and enhance the flow (quote 1’s truth). But if you increase the size too much relative to the volume of gas the velocity will fall and peak power will likely follow. Therefore, you want a balance between 2inch and 3inch for example to allow low rpm scavenging and high RPM flow without backpressure.

Quote 3 is rather amusing in that if there was nothing left to pull the exhaust gasses after the collector the exhaust gasses would come to a stop would it not? The scavenging effect continues in that exhaust gasses still have momentum and are thus still creating a low pressure area which still pulls gasses out of the exhaust. Therefore there is infact something left to pull the exhaust gasses after the collector. For those interested check this link to understand and visually see what is going on after the header/collector.

Sorry for the ramble but I felt it was necessary to prevent people from buying 3inch exhausts for their street driven Preludes with minor bolt-ons without understanding the consequences. Yes you will have more peak power and torque (but you will lose torque below 3K RPM, which you may or may not be able to live with on the street), but this extra top end power comes at the cost of atleast an extra 10dB, which may not be legal where you live or desirable if you wish to maintain the ability to hear till age 50. Therefore I said go 2.5 inch for NA in response to the question "what yields best results on an h22a1 with basic bolt on mods".
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Last edited by MilanoH22ALude; 05-18-2010 at 04:50 PM.
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Old 04-22-2010, 09:00 PM
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Re: exhaust piping diameter??

Valid point on the noise, But heres my solution to that:

Custom header with 3" collector
3" high flow CAT
3" resonators (x2)
3" Apex'i World Sport 2 (painted flat black lol)

This set-up will sound lik sex and still keep it uber quite.

Oh and completely agree don't run a 3" on my street or ill snipe you from my window.
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Old 04-22-2010, 09:03 PM
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Re: exhaust piping diameter??

Quote:
Originally Posted by 2.2Lude View Post
Valid point on the noise, But heres my solution to that:

Custom header with 3" collector
3" high flow CAT
3" resonators (x2)
3" Apex'i World Sport 2 (painted flat black lol)

This set-up will sound lik sex and still keep it uber quite.
Lol functional and stealth, way to roll! Two resonators will give it a much nicer growl.
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Old 04-22-2010, 09:04 PM
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Re: exhaust piping diameter??

Quote:
Originally Posted by MilanoH22ALude View Post
Lol functional and stealth, way to roll!
That's my goal.
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Old 04-22-2010, 09:51 PM
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Re: exhaust piping diameter??

I got a question, will a 3" yield good results from a H23 (non-vtec) too?
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Old 04-22-2010, 10:23 PM
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Re: exhaust piping diameter??

Honestly i would think so, seeing as the H23 has even more displacement than a H22
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