How high can you go on compression ratio before knock or being impossible to start?

cloakedvillain

cloakedvillain

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Obviously, higher octane fuel can handle higher compression ratios. I believe it was Jayraye that experimented with 95 octane vs 87 octane and found that with a 2 stroke, and at very high rpm the lower octane had more consistent combustion. Greater than 10:1 is used all the time on sport bikes but those are obviously designed and built for different uses than a gx50 or china doll.
 
If you're using stock parts, you probably won't get more than 8. A little stock engine is 6 and to get that to 10 would be a lot of machining.

To maintain a proper squish and combustion chamber swirl you can't take that much off. You would have to machine a whole new head to be able to reduce the volume enough.
 
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