Avoid the tendency to build on overly large header

While some gains might be realized if done properly and also used with very large exhaust systems, keep in mind that large headers and exhaust systems only really work at full throttle and at high engine speeds. Since most street driving is done at part throttle and at much lower engine speeds, performance will actually be reduced because the overly large headers (along with very large exhaust systems) will cause exhaust gas velocities to be from 14% to 30% slower most of the time which means that the header's ability to scavenge the cylinders properly will also be reduced by that same amount.

For most vehicles, the best street performance is obtained by trying to maximize average horsepower output over the entire rpm range - not just part of it. Street engines should produce decent horsepower from off-idle to the limit of the camshaft profile being used - in other words, from 1000 and up.

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2001 Honda S2000
201.63 whp : 135.74 ft/lbs