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73-87 Chevy _ GMC Trucks => Performance => Topic started by: mikewb on April 11, 2008, 04:26:11 pm
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i heard something about the 96-up heads needing more backpressure to run there best. anybody know about that?
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Mike, The whole "needs back pressure" is bunk! NO 4 cycle engine needs back pressure for optimum power, scavenging yes, back pressure NO. They will operate best with no exhaust leaks & some length of pipe past the exhaust port, but no back pressure. The amount of pipe is the key, go to the demolition derby & see "the guy" with the 8 single stacks up through the hood, it looks cool, but pops, ect. & truly is down on power compared to one with a 4-into -1 collected exhaust header/manifold. What your ultimately looking for is less than a few PSI of back pressure at WOT, measured before the muffler. When you have achieved this, "uncapping" the exhaust becomes near worthless. The reason drag race (& others) vehicles run "uncapped" is because this eliminates much the back pressure (bends/mufflers), however, quite often, a given amount of straight pipe is needed past the merge point of the header tubes for best results, so sometimes it's possible to GAIN power with an exhaust hooked up vs. just open headers (no collector extension) because this particular exhaust isn't restrictive for the power output, but likes to "see" a foot or so of pipe past the merge point or a H or X pipe is in place, but is gone with the open headers. Where's myth buster's when you need them? Isn't some of that show a riot? Lorne
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I would love to see this one on mythbusters.
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In a recent mag (Chevy Hi-performance I believe), they tested out an 18" long collector extension made an appreciable amount of horsepower gain over no extension on the end of a 4 into 1 header. I think it was around 15-20 HP on a 500 HP motor.
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In a recent mag (Chevy Hi-performance I believe), they tested out an 18" long collector extension made an appreciable amount of horsepower gain over no extension on the end of a 4 into 1 header. I think it was around 15-20 HP on a 500 HP motor.
That probably has to do more with the header collector design than backpressure
short collectors or headers with un-equal length tubes will benefit from an extension
collector design has a lot to do with it
(http://www.ssheaders.com/MergeCollectors.jpg)
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i think it was Low end torque in many engine's that like a little back-pressure,,,think it has to do with the pulse wave