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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