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Old 06-14-2013, 12:13 PM   #10
RecoveringSaabaholic
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Join Date: Jun 2010
Chapter/Region: NESIC
Location: Portland, ME
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2006 Impreza 2.5i
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Quote:
Originally Posted by PA-Outback2000 View Post
kenny d... define big plans

saabaholic... you are talking about EL (equal-length) headers, as they move powerband higher in rpms. my dyno graphs show a gain of 18TRQ to the wheels with just the borla header. yes, the stock header is UEL, but a crappy version of one. definitely get the borla header. it's worth the price.

dyno... http://xcceleration.com/imp-gallery-...back.25.na.htm
My bad, I was under the impression that EL headers utilized the pressure waves created by the exhaust pulses to help draw the exhaust gasses out of the cylinders. This would result in an increase in torque depending on the size of the primaries, as the velocity of the exhaust gasses would vary with the size of the primaries, and determine what RPM range that torque boost would fall into. So for my particular case, where I have EL but larger primaries, I would see a slightly higher peak torque that occurred slightly higher in the RPM range, as well as a slightly higher peak HP in high RPM range from the larger diameter primaries and resultant better flow of exhaust gasses.

However, for UEL folks, they would not get the benefit of the harmonics in the headers, and would not see the same torque boost. They would still see a bit more high RPM HP from the increased exhaust flow.

Of course this is all just theory, and only a before/after comparison on a dyno will tell the whole story. Also, any additional mods (like a cat back cams or intake) will change the dynamics of the system.
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