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Dirt Bike Discussions By Brand
Dirt Bike Brands - Other
XR440 kit
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[QUOTE="Rich Rohrich, post: 141884, member: 16241"] Keep in mind the MON (or motor) octane rating of the fuel is the significant spec in this case. There are a number of race fuels with high overall octane numbers (> 100) but a large gap between RON and MON octane ratings. High RON rated fuel without comparable MON rating is fairly useless in an air cooled XR. PJ - Don't forget to remind these guys that the (MON) octane the engine will require is dependent on the CR and the cam they are running, specifically how late the intake valve closes. The later the intake valve closes the lower the MON octane required (all else being equal). Running a 12:1 CR with the stock XR cam run (at stock lobe center angle) will generate very high cylinder pressures and an enormous amount of heat and in my opinion it's not a good idea regardless of the fuel you are running. It's not a coincidence that Honda matched a relatively low stock compression ratio with the stock early intake close timing. :) Trailryder - Unless your rides are short and the engine only sees light loads it's best to be conservative with the CR on these engines and make sure you match the compression ratio and cam timing carefully. Don't forget it's still an air-cooled engine :) [/QUOTE]
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Dirt Bike Discussions By Brand
Dirt Bike Brands - Other
XR440 kit
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