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2011-2014 Mustangs
Exhaust
Long tube headers, which Primary size is 'best'?
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<blockquote data-quote="Shaun@AED" data-source="post: 15190757" data-attributes="member: 32381"><p>Yes, absolutely.</p><p></p><p>The negative pressure pulse of the exhaust gasses should be at the exhaust valve when it is open on the next combustion cycle during the overlap phase in order to pull more exhaust thru the chamber and increase power output. The Length of the primaries determines the RPM at which this 'boost' in airflow thru the chamber will occur. The shorter the primary, the higher in the RPM band at which this will occur, the longer the primary the lower in the RPM band.</p><p></p><p>We've found via testing that the Kooks midlength headers have a boost in power around 6700-6800RPM. Longer primaries like ARH, Pypes, SW, and others give power boosts at much lower RPM's. With Cam timing changes we can move this RPM to some degree, but not much. Primary diameter can affect this as well if the gases slow down significantly due to the larger tube they have to fill. Slower exhaust gasses = lower RPM at which the negative pressure at the valve will occur, and it could also negate much of the effect of the negative pressure if the gasses slow down too much to fill the primary. IE, you CAN go 'too big' and hurt performance.</p><p></p><p>Basically the Shorty headers available are a bit too short for boosting power in the usable RPM range of these engines, and the long tube headers are so long they give benefits to mid range torque. The Kooks seem to be the best fit overall, although they are not perfect IMO.</p></blockquote><p></p>
[QUOTE="Shaun@AED, post: 15190757, member: 32381"] Yes, absolutely. The negative pressure pulse of the exhaust gasses should be at the exhaust valve when it is open on the next combustion cycle during the overlap phase in order to pull more exhaust thru the chamber and increase power output. The Length of the primaries determines the RPM at which this 'boost' in airflow thru the chamber will occur. The shorter the primary, the higher in the RPM band at which this will occur, the longer the primary the lower in the RPM band. We've found via testing that the Kooks midlength headers have a boost in power around 6700-6800RPM. Longer primaries like ARH, Pypes, SW, and others give power boosts at much lower RPM's. With Cam timing changes we can move this RPM to some degree, but not much. Primary diameter can affect this as well if the gases slow down significantly due to the larger tube they have to fill. Slower exhaust gasses = lower RPM at which the negative pressure at the valve will occur, and it could also negate much of the effect of the negative pressure if the gasses slow down too much to fill the primary. IE, you CAN go 'too big' and hurt performance. Basically the Shorty headers available are a bit too short for boosting power in the usable RPM range of these engines, and the long tube headers are so long they give benefits to mid range torque. The Kooks seem to be the best fit overall, although they are not perfect IMO. [/QUOTE]
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Long tube headers, which Primary size is 'best'?
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