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01-31-2008, 06:51 PM | #1 |
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Fixed exhaust- is it torquier?
so i got my exhaust fixed from the cat back and being loud, getting pulled over 3 times in 2 weeks. so now she's super quiet again and it also seems like it has a bit more torque. would this be from added back pressure-or just that it goes without being noisier than hell?
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01-31-2008, 07:28 PM | #2 |
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i was running my last project car on an open header (straight 6) and as soon as i put a exhaust on the thing really woke up.. theres science behind it. having an properly tuned exhaust aids in cylinder filling, by effectively removing exhaust gases before IVO and during overlap.
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01-31-2008, 08:06 PM | #3 |
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It works because the manifold isn't tuned. Normally in a tuned system you have the header consisting of the 4 primary pipes from each exhaust port, of a particular diameter and length, and coming together into a collector area, also of a particular diameter and length.
In theory, everything that controls the actual flow behavior and tuning of the exhaust is done via the header/collector only. Everything after this is essentially meaningless, if done right. Now on most stock setups, there really is not much for tuning. Most primary piping is not equal in length, nor is there any real collector area nor any termination of the collector piping. The whole exhaust turns into part of the "system," and it can influence the overall behavior. http://www.superchevy.com/technical/...exh/index.html |
01-31-2008, 08:10 PM | #4 |
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ah! thanks!
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01-31-2008, 08:10 PM | #5 | |
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Quote:
sounds better than what i said. although i do dissagree that everything after a collector is meaningless, especially on a car with more than one cylinder bank. H and X pipes have been dyno proven to increase power. |
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01-31-2008, 08:33 PM | #6 | |
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And tubing diameter is important on n/a cars to keep the exhaust gas velocity as high as possible without being restrictive... also, changing tubing diameter can hurt, sometimes a lot. changes in velocity, from slow to fast or fast to slow will hurt performance and the more changes in velocity (changes in tubing diameter) the more it will hurt performance. I dont know any formula to determine optimum diameter but i im sure there is one. the 2.5L subaru n/a motors are best around 2.25" ID under 200HP. The guys @ TWE said if aggressive cams are used or other mods that will make power over 200hp, a larger diameter tubing will be beneficial. seems like a rough rule of thumb but probably a good one since they are just about the best when it comes to subaru exhaust. |
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01-31-2008, 08:39 PM | #7 |
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oh yeah, my new pipes are a bit smaller than the "stock" ones that literally fell off. maybe they're better this way.
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01-31-2008, 08:41 PM | #8 |
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The back pressure will help keep the air fuel charge in the cylinder on the very begining of the intake stroke, instead of it flying out the exhaust valve.....during valve over lap.
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01-31-2008, 11:54 PM | #9 |
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But this is what you want. You need that flow from the intake side to clear out the spent charge from the combustion chamber. This is the whole idea behind scavenging.
Backpressure is always bad. You're running a big air pump. You don't want restrictions. Restriction = inefficiency. |
01-31-2008, 11:58 PM | #10 |
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i experienced the same thing.i definetly noticedmore torque gains
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02-01-2008, 12:13 AM | #11 | |
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02-01-2008, 04:46 AM | #12 |
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Wait...are you talking about exhaust scavenging? Cause...it's the exhaust gases leaving the exhaust that creates the slight vacuum to pull in fresh air from the intake side accelerating the air/fuel mixture...
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02-01-2008, 10:02 PM | #13 | |
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02-02-2008, 11:53 AM | #14 |
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have a 97 L 2.2 SOHC, Borla 4-2-1 header, new oem converter, 2.25" mid-pipe with no resonator and 3ARacing muffler with silencer in it, noticeable torque gain with the silencer in, extremely doggy with it out, not sure why
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