Header design
(→Primary tube length) |
(→Argument for equal primary tube lengths) |
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In the header photograph to the right, the short primary tube would scavenge at a higher RPM and the long primary tube would scavenge at a lower RPM for the respective cylinder. Therefore the cylinder with the short tube will be running lean at low RPM and the long tube cylinder will be running lean at the high RPM and would require different jetting and timing than the others. How do you do that with a standard kettering distributor and a simple carburetor? That's why equal length is important: so you can tune your car. Not only do equal length tubes make the engine tuneable, but make more torque in the RPM range for which they were intended. | In the header photograph to the right, the short primary tube would scavenge at a higher RPM and the long primary tube would scavenge at a lower RPM for the respective cylinder. Therefore the cylinder with the short tube will be running lean at low RPM and the long tube cylinder will be running lean at the high RPM and would require different jetting and timing than the others. How do you do that with a standard kettering distributor and a simple carburetor? That's why equal length is important: so you can tune your car. Not only do equal length tubes make the engine tuneable, but make more torque in the RPM range for which they were intended. | ||
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| + | This is particularly true for V6 engines. In the case of the 173ci 3.1L or the 3.4L pushrod engines, the pulse of the air pressure wave, as well as the sound wave, need to dissipate at a particular length so that a proper negative wave travels back AT THE RIGHT TIME to the exhaust valve, aiding the exhaust flow. In the case of the GM pushrod v6's the firing order is sequential and therefore cylinders fire on alternate sides of the block on each compression stroke. Generally, those v6 engines operate best with 1.5" pipe and a primary length of 32" to 36" depending on the compression and torque curve desired. It should be noted that most headers used for the FWD and Mid-Engine v6's are not optimum in performance. | ||
=====Argument against equal primary tube lengths===== | =====Argument against equal primary tube lengths===== | ||
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