Why 66cc/80cc? Which is it?

[TheNewbie]

This might be a stupid question... But I've tried searching and I'm not really coming up with an answer.

Why do they advertise two engine sizes? How big are these engines? Are there 2 ways to put them together or something?

 

[MotorBicycleRacing]

It's marketing hype or to be blunt lies.

The story is that the Chinese count the volume of the combustion chamber to
make up the 80 cc from 66 but that story breaks down when you see they don't
measure the 48 cc motor in the same exaggerated way.

China bike engine factories have always advertised their biggest engine as 80cc. However, the bore and stroke of an 80cc being 47x38mm only equals 66cc. Therefore there is no such thing as an 80cc bike motor and it truly does not exist. This is the biggest motor available.

 

[TheNewbie]

That makes sense. Thanks!

 

[wally]

Easy! A lot of places specify 49cc as the biggest motor where a liscence is not needed. Doesn't 80cc sound BIGGER than 66cc? Yes you are correct in saying that the total volume is compared with swept voulume.
And swept volume is correct at 66cc but 80 sounds faster!