Header power gains
- Thread starter Mustangog2003
- Start date
I've got a set of Kooks on my car and although I'll stand by their quality of workmanship and “real” Jet Hot Ceramic Coating whole heartedly, I really doubt they're making any more power than any other mid length or long tube header on the market.
Long tubes are great, but their really long primary lengths are not necessary for our cars smaller 281cid displacement in order to make their most power and torque. They're convenient for the manufacturer, since they bring the collector out of the engine compartment and along the lower body line of the car, which makes manufacturing and fitting a matching mid-pipe that much easier. This is the primary reason a lot of manufacturers will choose the long-tube over mid-length design in the first place. Not because they make any more power or torque. Were our engines a larger displacement, the longer primary tubes would be warranted, but truth be told, in this case mid-length headers will perform just as well as a set of long-tubes.
.....and either style header will perform much better than a set of shorties. Which are made primarily because of their lower cost and small packaging. Optimum flow characteristics often have very little to do with their design.
Long tubes are great, but their really long primary lengths are not necessary for our cars smaller 281cid displacement in order to make their most power and torque. They're convenient for the manufacturer, since they bring the collector out of the engine compartment and along the lower body line of the car, which makes manufacturing and fitting a matching mid-pipe that much easier. This is the primary reason a lot of manufacturers will choose the long-tube over mid-length design in the first place. Not because they make any more power or torque. Were our engines a larger displacement, the longer primary tubes would be warranted, but truth be told, in this case mid-length headers will perform just as well as a set of long-tubes.
.....and either style header will perform much better than a set of shorties. Which are made primarily because of their lower cost and small packaging. Optimum flow characteristics often have very little to do with their design.
jivepepper
Founding Member
That would be Mac and they're an absolute junk Header and in some cases have actually proven to do more harm than good. Next question.
I bought my used pos mac's for 75 bucks used a year ago and installed them myself. I noticed a nice again as soon as I drove it. Used macs FTW!!
Stan Weiss
Member
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.
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.
LaserRed01GT
Banned
The way I understand it is this. Header primary diameter/length, collector diameter/length, and collector throat design are all determined by engine displacement, RPM at which the motor makes peak torque, exhaust valve diameter, exhaust port volume, EVO (exhaust valve opening – degrees ATDC) and horsepower. You also have to consider the vehicle weight , shift points, and trap RPM to fine tune the header. A heavier vehicle will spend more time in the lower RPM range than a lighter vehicle. Shorter primary tubes tend to make more power under the curve in the higher RPM range, and the longer tubes are usually favor making more power under the curve in the lower rpm range.
The target primary length has a direct relationship to EVO and peak torque RPM. The target primary diameter has a direct relationship to engine displacement and primary length. The target collector length has a direct relationship to the primary length and peak torque RPM. The target collector diameter has a direct relationship to horsepower and primary diameter. The collector length/diameter will usually prove to have more of an effect on the power curve than the primary length. A commonly accepted rule of thumb on collectors is that shorter, larger diameters favor top end while longer, smaller diameters favor the low end.
I made a simple calculator in Excel to “estimate” the header dimensions based on displacement, EVO, and peak torque RPM. This is obviously not the end all be all way to build a header, but it will get you pointed in the right direction:
Right Click and Save Target As:
Header Dimensions Calc
The target primary length has a direct relationship to EVO and peak torque RPM. The target primary diameter has a direct relationship to engine displacement and primary length. The target collector length has a direct relationship to the primary length and peak torque RPM. The target collector diameter has a direct relationship to horsepower and primary diameter. The collector length/diameter will usually prove to have more of an effect on the power curve than the primary length. A commonly accepted rule of thumb on collectors is that shorter, larger diameters favor top end while longer, smaller diameters favor the low end.
I made a simple calculator in Excel to “estimate” the header dimensions based on displacement, EVO, and peak torque RPM. This is obviously not the end all be all way to build a header, but it will get you pointed in the right direction:
Right Click and Save Target As:
Header Dimensions Calc
Stan Weiss
Member
I never said CI was not used. >>> I do not remember CI being a controlling factor. <<<< I stand by the statement. It is just one of a number of factors used.
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