Tube headers

[robo]

Interesting bit on tube exhaust manifolds. Extract from an article.



The second biggest controversy in header design is the "equal length" versus "shorty" styles - which is best? Like most performance products, there are advantages and disadvantages to both.

Exhaust headers with equal length tubes have been shown to develop slightly more power on an open exhaust system, but not when hooked up to a street system with mufflers. Fact is, most street motors with shorty headers will produce the same power as they would with expensive equal length headers.

Equal length tubes can produce more power, but they have to be the right length for the specific motor at the RPM range where you want the power. What that means is lots of custom fabrication and dyno testing, which translates into lots of time and money.

For racing applications, the slight gain may justify the cost, but competition cars can be more easily built "around the engine" than street cars. When you're working within the confines of a given body style and chassis, with motor mounts, starter, steering linkage and accessories to think about, the way the headers fit become more important.

That's where the compact or "shorty" style header shines. You get a significant performance increase compared to stock exhaust manifolds, at an off-the-shelf price. Plus, Sanderson headers provide excellent clearance around spark plugs, starter and chassis components, as well as ground clearance for lowered vehicles. The charts on this page illustrate just how little power you trade off for the much lower cost and easy installation of compact headers.

Horsepower vs Torque as a function of header tube length




Bob

[baz-r]

this is purely a harmonic thing and would be diffrent for every engine its state of tune its also dependent on wht rpms you want your power to be
engins design speed, exhaust valve timing and its duration is what will denote how header length will work to benifit.
a good length will make a pressure wave to create a low pressure at the exhaust valve pulling air/fuel in to the cyl at valve overlap (good scavanging) and a bad length will have the pressure wave reflected back making a high pressure at the exhaust port (poor scavanging) pushing exhaust back in

there is no magic header length or style that suits all engines its more of a case of finding what works best for what you have
equal length for equal cyl power ballance.
longer headers genraly work better at higher rpms.

spent months at uni on this stuff