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Old 12-30-2012, 06:45 PM   #84
because I can
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 9,116
Originally Posted by motu View Post
Revs - I've been lead to believe it's a bit unsafe to rev an Airhead too high, but my R65 loves to spin to 8,000rpm. I use it as an over rev when I have runaway wheelspin on gravel roads, better to let it go than risk an upshift or back off in a powerslide, but also when the red mist is down and shifting by ear, my shift point seems to be 8,000rpm. I've been reading about the Michel 850 kit for the R65, and they say it spins to 9,000rpm. So long as I have no valve bounce, is it ok to run them at these revs ?

It reminds me of the Honda XLV750 I had - max hp at 7,000, red line at 8,000 and limiter at 8,250. I had that bike on a dyno a couple of times and the power curve was exactly the same a Honda's - it only lost a couple of hp between 7,000 and 8,000rpm. I used the over rev on gravel too, but also to save wasted upshifts between corners on the road - let it spin out to 8,000 and then into the next corner. I'd like to do this with the R65 too.
Exactly! That is what usable over rev is all about. It is very often very handy to reduce lap times! I haven't figured R65 average piston speed per second. The rest of the bikes at a 70.6 stroke are under 4000fps until just short of 9000rpm. IMO there is no need for a shorter stroke than 70.6 since the valve train is the limiting factor at that stroke, let alone a shorter one. Plus the bore to stroke ratio of a R65 is already 1.33:1. The same as a R100. That's already quite the short stroke considering our head design!!!! Any shorter bore to stroke ratio is barking up the wrong tree IMO.
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