How to measure header collector length?
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Re: How to measure header collector length?
Larry's calculations read to as many as three decimal places, but that doesn't mean you can measure the effect of a 16.3" collector Vs. a 16" one...
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Alan Roehrich
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Re: How to measure header collector length?
Bill is correct. In most cases, 0.250" or even 0.500", may not make a difference, and Larry will tell you that. The 3-4 decimal places are simply the result of using more accurate math, much like carrying "pi" 10 to decimal places rather than the usually quick and dirty 3.14. You often cannot get the primary lengths that close to ideal length either, and possibly not that close to equal.
There are "rules of thumb" for this. The diameter(s) set the peak HP and peak torque RPM, then using the shorter ideal length fattens the power curve above the peak, using the longer ideal length fattens the curve below it. So, if you look at PipeMax it will give you 3 "ideal" or "tuned" lengths. The latest version of PipeMax will give you lengths and diameters that will yield higher RPM and higher peak power, as well as lengths and diameters that yield more power at lower RPM and usually a flatter power curve.
If your headers are on the short side, and/or large diameter side, you make the "choke" or venturi of the merge smaller, to regain some velocity, you can use a longer collector as well. A header that is too small and/or too long will probably not want a merge collector at all, but rather a straight, single diameter collector, at the shortest tuned length.
There are "rules of thumb" for this. The diameter(s) set the peak HP and peak torque RPM, then using the shorter ideal length fattens the power curve above the peak, using the longer ideal length fattens the curve below it. So, if you look at PipeMax it will give you 3 "ideal" or "tuned" lengths. The latest version of PipeMax will give you lengths and diameters that will yield higher RPM and higher peak power, as well as lengths and diameters that yield more power at lower RPM and usually a flatter power curve.
If your headers are on the short side, and/or large diameter side, you make the "choke" or venturi of the merge smaller, to regain some velocity, you can use a longer collector as well. A header that is too small and/or too long will probably not want a merge collector at all, but rather a straight, single diameter collector, at the shortest tuned length.
Re: How to measure header collector length?
Ok, if I measure from the end of the primaries I get 23". In pipemax it says that 23" is the length that there will be hp/tq loss. The mufflers were added on after the headers without cutting the collectors. Can I just make a taperd choke to 3 3/4 and put it in the straight collector. If so do I just put it right at the back or is there a calculation for the location of the choke?
On an interesting side note. There is a faint heat mark on the header in the ceramic coating and when I measure 16.3" from the primaries it is within 1/2 of that mark
On an interesting side note. There is a faint heat mark on the header in the ceramic coating and when I measure 16.3" from the primaries it is within 1/2 of that mark