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MX, SX & Off-Road Discussions
Dirt Bike Mods & Maintenance
Whats All This Fuss About Crankshaft Smoking?
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[QUOTE="EricGorr, post: 382698, member: 19611"] SFO: Virtual Two-Stroke, a design and simulation program available from Optimum in Bridgeville PA enables you to hone in on any part of the powerband. So imagine that you have data aquisition on a supercross bike. And you know that a factory rider keeps uses a narrow rpm and gear selection. And you calculate that it takes a certain amount of torque to accelerate a motorcycle and rider to clear any given obstacle. The program enables you to change dimensions of the engine and immediately see the results on a dyno chart. But for a license fee of $12k a year, it better do something spectacular ;) Steve: In 1988 Rich and I were splitting apart old 1986 RS250 roadracer cranks to extract 110mm connecting rods to install on CR125s. Back then you couldn't buy the rods, only complete cranks. This gives a rod ratio of just over 4:1 which is the empirical standard for an engine that runs in the 10-13,500 rpm range. Forget about leverage and torque, Honda is trying to get the piston to dwell at TDC longer for a greater pressure rise during combustion and accelerate the piston from BDC in order to gain more reed petal lift and longer duration from the intake phase. The spacer plate is needed because they can't relocate the piston pin closer to the crown. Using a plate increases the crankcase volume, and that may be a good thing in order to capture the extra volume during the intake phase. But then again Honda may be stuffing the crankcases with epoxy to compensate for the volume change of the plate. One things for sure, they've tested every conceivable combination. Regarding the displacement of the engine, I'm sure that its only 125cc. [/QUOTE]
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MX, SX & Off-Road Discussions
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Whats All This Fuss About Crankshaft Smoking?
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