Header design
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That brings me to primary length. Let me begin by saying, those "shortie" headers are not headers, just tubing manifolds designed for clearance and not horsepower or torque. I know they look like they would flow better than manifolds and probably do in many instances, but unless you are running a supercharger, you need more than flow out of a header. The bothersome part of the "shortie" (other than length) is that the collector is so short and causes a lot of turbulence right where the flow needs to be smoothed out. | That brings me to primary length. Let me begin by saying, those "shortie" headers are not headers, just tubing manifolds designed for clearance and not horsepower or torque. I know they look like they would flow better than manifolds and probably do in many instances, but unless you are running a supercharger, you need more than flow out of a header. The bothersome part of the "shortie" (other than length) is that the collector is so short and causes a lot of turbulence right where the flow needs to be smoothed out. | ||
| − | I know a lot of you guys are using them and are happy with them, but Hot Rods are about making things better, faster and more efficient | + | I know a lot of you guys are using them and are happy with them, but Hot Rods are about making things better, faster and more efficient aren't they? Just giving some food for thought. |
Anyway, back to primary tube length - most street engines that are operated in the idle to 5500 range (yes, your 350 may rev 6500, but is it making any power up there?) work very well with 36"-38" primary tubes. This is the length necessary for the shock wave in the tube to reflect back to the exhaust valve and create a vacuum which will suck the burnt gasses out of the Combustion chamber. This is provided that the primary tube has the proper diameter to keep the velocity of the gasses up. | Anyway, back to primary tube length - most street engines that are operated in the idle to 5500 range (yes, your 350 may rev 6500, but is it making any power up there?) work very well with 36"-38" primary tubes. This is the length necessary for the shock wave in the tube to reflect back to the exhaust valve and create a vacuum which will suck the burnt gasses out of the Combustion chamber. This is provided that the primary tube has the proper diameter to keep the velocity of the gasses up. | ||
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| + | Another thought - equal primary tube length. If the length of the primary is part of the tuning equation, how well does an engine run with different primary tube lengths? Try and jet that carburetor without pulling your hair out! Most of the commercially availble headers out there have a large variance in tube length. Check out a set for a big block mopar in a B or E body for an example. I have measured a 16" variance from longest to shortest tube on these units. | ||
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| + | This would mean that the shortest primary tube would not create a scavenge for that cylinder, so that cylinder would not make the same power as the others, and would require different jetting and timing than the others as well. How do you do that with a standard kettering distrubutor and an simple carburetor? | ||
Now we get to the collector - ever see a header with 1 5/8" primaries that had a 2 1/2" collector? No, me neither. But that is the optimum diameter for most street headers. Run that right into a 2 1/2" exhaust and you have a sweet system, lots of torque where you need it and better fuel economy. The collector should have a gentle smooth shape from the four tube area down to the final diameter as well to keep things moving smoothly. | Now we get to the collector - ever see a header with 1 5/8" primaries that had a 2 1/2" collector? No, me neither. But that is the optimum diameter for most street headers. Run that right into a 2 1/2" exhaust and you have a sweet system, lots of torque where you need it and better fuel economy. The collector should have a gentle smooth shape from the four tube area down to the final diameter as well to keep things moving smoothly. | ||
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