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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Squish bands
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[QUOTE="jaguar, post: 1432530, member: 19340"] Squish head compression: 170psi compr ratio: 10.3 squish band width: 6mm squish band area: 48% clearance: .65mm velocity: 16.4m/s delayed ignition overall impression: ran good but not noticeably better top speed: 57.7kph (which is 35.9 mph) top temp F: 390 Non-squish head compression: 170psi compr ratio: 10.3 overall impression: ran good top speed: 53.5kph top temp F: 340 But I had set my adjustable ignition to be delayed a bit and forgot to return to normal setting for the non-squish head test. Now it's dark and my batteries for my lights need recharging so I will continue testing tomorrow. Gordon Jennings wrote: "no [mass produced] 2 stroke engine in my experience had ever tolerated cranking pressures above 175psi". I can't tell any power difference between the two heads, both at 170psi. But the one with the squish band lets it rev out further. That is when I am using an expansion chamber. It either is increasing the top end power or it is causing the exhaust gas to be hotter which affects sound wave speed which extends the pipes powerband. Next I need to test them using only the stock muffler because it won't be affected by exhaust temperature. The squish band head runs hotter at 390 degrees vrs 340 for the regular head. I used a modified Jaguar CDI to test it. I reduced the normal input resistance to delay the ignition. And it liked no secondary jumper so I just redid the CDI for even more top rpm ignition advance. I will probably start making them with the extra adjustability for people using these heads with squish band. The 50 extra degrees doesn't worry me since it is borrowed from the piston, which is a good thing. What worries me is the 170psi. That is higher than most motocross bikes. It will shorten the life of the conrod bearings, no doubt. I may reduce the pressure in the normal head to 150psi for continued testing and I'll leave the other head at 170psi since that parallels heads being sold. [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Squish bands
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