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I have a motorcycle with compressor ratio is 11.5:1 .
It is possible to upgrade turbo for this engine ( keep stock internal engine and using Ron 95 petrol ) .
Thanks for addvances
The answer is that yes, you will be able to turbo the engine even with 11.5:1, however on a 95 octane fuel you are almost certainly going to be knock limited so you will need to be quite careful with your tuning. I'd also suggest that you're going to want to keep the boost quite low (I'd start with around 5 psi) in order to avoid knock and the requirement for excessive ignition retard.