The length of the pipes from flange to the top crotch of the header needs to be 21-22 inches, measured through the middle of each curve. No shorter, no longer. Length is determined by the shock wave distance traveled during the cycle of the valve opening and closing. The slower the engine is turning, the longer the distance of wave travel. At WOT & 11,000 ERPM that distance is very short and you can take the pipes off and run a 3" stub if you want. But then you are either running idle or WOT, there is nothing in between.I got the exhaust system laid out and have the primary tubes tacked together. I used the original flanges, the flexible couplers, the merge collector and tailpipe. I tried to keep the primaries equal length. A couple tubes moved when I tacked them so they are approximately equal length. I have a feeling they are close enough!
It was quite a puzzle! There were several ideas that didn't work out but I like how it ended up. I am going to hang it on the airplane before I finish weld it. I have a muffler to fit up and hang up somehow. The tailpipe may need to be adjusted for the muffler so final welding will wait.
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I agree, Marc! I've been flying a stock, 145HP Yamaha Genesis RX1 which weighs about 160-170 lbs installed since 2012, lol. And when all was said and done it cost me but $600 for the engine with 2000 miles on it, just enough to break in the rings and bearings. Most people recognize it as 140HP engine but later dyno tests after the sleds were broken in proved 145 HP time and again.140 HP from 160 lbs. is not bad! Time will tell if it is practical with that engine.