Header design
(→Summary of header design principles) |
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Using V = 1700ft/sec the equations simplifies to | Using V = 1700ft/sec the equations simplifies to | ||
| − | L = 204,000/rpm. | + | L = 204,000 inches/rpm. |
There have been various permutations on this basic design like tri-Y headers, stepped tubing size, etc. Each takes advantage of modifying the pressure pulse arrival time at the instant the exhaust valve closes to achieve a scavenging/ higher volumetric efficiency/ more torque result. The good is that you can achieve a very significant torque increase at the design rpm. The bad is that you likely will also achieve less torque at other RPMs. | There have been various permutations on this basic design like tri-Y headers, stepped tubing size, etc. Each takes advantage of modifying the pressure pulse arrival time at the instant the exhaust valve closes to achieve a scavenging/ higher volumetric efficiency/ more torque result. The good is that you can achieve a very significant torque increase at the design rpm. The bad is that you likely will also achieve less torque at other RPMs. | ||
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As you can see from this discussion, most popular aftermarket headers are poorly designed for any performance purpose. Tubes are too short, too big, and all different lengths. Most "street rod" headers are not designed for performance, rather to fit insde the typical smoothie envelope. "Performance" headers are desinged to look zoomie I guess because I can't figure out any other design criteria when I study them. | As you can see from this discussion, most popular aftermarket headers are poorly designed for any performance purpose. Tubes are too short, too big, and all different lengths. Most "street rod" headers are not designed for performance, rather to fit insde the typical smoothie envelope. "Performance" headers are desinged to look zoomie I guess because I can't figure out any other design criteria when I study them. | ||
| − | Incidentally, this is the principle that Chrysler used on the cross ram intake manifolds they put on big block passenger car engines in the late 50s. The velocity of sound in the cold intake gasses is much slower than that in hot exhaust so tuned | + | Incidentally, this is the principle that Chrysler used on the cross ram intake manifolds they put on big block passenger car engines in the late 50s. The velocity of sound in the cold intake gasses is much slower than that in hot exhaust so tuned length for a street intake is much shorter @ about 18" from the valve seat to the plenum. Thus they put a 4bbl carb on either side of the engine and crossed over long ports. Looked and performed great! |
====Equal primary tube length==== | ====Equal primary tube length==== | ||
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