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Yamaha MX & Off-Road Dirt Bikes
Squish bands
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[QUOTE="sbest, post: 1436180, member: 124334"] Jaguar, are you the same guy from the McDizzy List? Nice hearing from you. My work has been on 125-300cc KTM, Yamaha and Honda 2 strokes and bike and automotive 4 strokes. I played with squish areas, bowl shapes and volumes, and squish gaps. Results tend to deliver in a "Bell Curve" fashion with a bias one way or the other, for example squish gap in these engines is ideally 0.030" to 0.040" and gets bad fast if reduced to 0.020" but is still acceptable at 0.060". I found high rpm and smaller engines need less squish area % at rpm, but that more squish area helps to fill in the torque and make these engines less peaky. More squish area (and deeper bowls) does take some power at max rpm at comparable cranking pressures, but make more power by allowing higher cranking pressures and increasing mid-range power to increase the average and tame the powerband. Hemispherical and shallow bowls tend to favour high rpm power production, toroidal and deep bowls favour mid-range power and a sharp rpm cut off in my experience. If I was building a high revving geared street motor I might tend to go low percentage squish area with a shallow hemi bowl and moderate compression to not blow heat into the piston. Squish and compression are for the low and mid rpm range. High rpm want a smooth head surface to sweep clean. Squish speeds up the burn so it needs less advance. Gordon Jennings was my guru in the 1970s but this is 40 years later. Many advances have been made but it is amazing his work is still so valuable today. "The 2stroke Tuner's Guide" is definitely the first book to read on 2 strokes. Steve [IMG]https://scontent-a-iad.xx.fbcdn.net/hphotos-ash2/t1.0-9/427174_10151168912820803_1690350583_n.jpg[/IMG] [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Squish bands
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