What kind of RPM on a China Girl?

[Nashville Kat]

Does anyone know what kind of RPM a "stock-ish" (not terribly modified) China Girl 2 cycle motor might turn at- at say- near, but not full throttle?

Just wondering....

 

[Dan]

Hey Kat!

I forget but have a tach and doing a china girl build. So can let ya know when done. I think it was 75K at cruising? But really don't know for sure. Will check though.

 

[MotorBicycleRacing]

If you know your speed, gearing and wheel diameter you can calculate rpm.
Race motors are over 9000 rpm.

 

[crassius]

yeah, big diff between 36T sprocket and 44T

 

[kaneto]

My totally stock 66 cc with 44 tooth (standard) rear sprocket on a hardtail bike with 26" x 1.95 tyres is maxing out at just under 6500 RPM given the fact that I'm weighting 96 kg (210 lbs)

 

[Citi-sporter]

Certainly there's a fair difference between the 66 and 48 cc engines on average, more cubes more power, higher RPM?

 

[crassius]

in practice, with same rear sprocket and same weight of rider, the smaller motor will get a bit higher RPM due to less weight of piston - it will take it longer to get to top speed though

 

[Dan]

in practice, with same rear sprocket and same weight of rider, the smaller motor will get a bit higher RPM due to less weight of piston - it will take it longer to get to top speed though

Thats really interesting and makes sense.

Never would have thought of that. But is the first in chain of events.

Crass, is that in part why cutting windows in the piston is to your advantage?
(forgetting the terminology)

 

[crassius]

most mods to the piston are aimed at changing port timing and duration (esp. windows for reed valve motors) - lightening wrist pin would be just for weight though