Header power gains

Stan Weiss said:

I guess the design parameters for headers have changed. I do not remember CI being a controlling factor. At its basics higher RPM short tube length lower RPM longer tube length. More HP larger tube diameter, less HP smaller tube diameter.

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They've certainly changed....they've evolved. No longer are we in the era of "throw big exhaust on it, a cam, intake and a carb and run 12's"

Engine displacement and power output is an absolute crucial factor in determining how to properly select a header. Not just operation range. Generally, large diameter, longer primary lengths are selected for higher output and/or larger displacement engines and smaller diameter, shorter primary lengths are selected for smaller displacement engines.

Superford Magazine published independent testing results years ago involving most of the main brand header manufacturers that showed smaller displacement street oriented engines like the 5.0L & 4.6L often showed no further improvement and in some cases actually responded better when the primary lengths ranged approximately 27" and diameters were kept more conservative. It stated that since the breathing capabilities of the smaller displacement (around 300cid) engines were less than that of even the lower output big displacement, big block engines of the earlier era. Designing a Header with maximum primary length and large diameter was no longer the optimum method used to scavenge and efficiently transfer exhaust gases.

Smaller diameter primaries will often limit horsepower potential, yes but they also boost low end torque. If you’ve got an engine that isn’t capable of breathing and making horsepower beyond a certain point, would it make sense to bolt on a set of “cookie cutter” headers designed for a “one size fits all” application? The reason you'll see companies promote "shorty" headers for higher RPM applications, is because they've not got the room to incorporate the use of large primaries and/or collectors into a longer tube design, so they compensate by shortening the primary length. This works out well for them, since it makes the header cheaper and easier to package. But the notion that shorty headers perform better at higher RPM is purely a myth. No shorty header will outperform a "properly" designed long tube header at any operation range or RPM!

This is why custom headers (like Kooks) are so expensive. Not only will they design a header with the best fit and finish in mind, but they’ve taken the time and effort to designed around the breathing parameters of the particular engine within a specified operation range and probable power outputs. This includes customizing and optimizing primary shape/diameter, lengths as well as collector design. Most of the name brand headers (BBK, MAC, HEADMAN, HOOKER, etc) design their headers with two things in mind.....cost and fit. Performance always takes a back seat.....even with their long tube headers.

Don’t get me wrong, that’s not to say they’re no good, or that some research hasn’t been done to ensure that their headers perform properly over a wide range of power levels or RPM. But they’re more of a ballpark design, rather than an exact science.

I know this sounds like a contradiction to my original statement about my Kooks headers probably not making any more power than most mid-length and long tube designs on the market. But what works against me, is the car that they’ve been installed on. I did get the best possible header available.....without a doubt, but room is a serious issue where the MN12 chassis is a concern. Had there been more of it to work with, I’m confident the header could have been more tailor made to the application.