Anyone Know? Compression Difference..

[JabberJaw]

Does anyone know what the difference in hp one would gain by changing from a 89.0mm 10.5:1 piston to an 89.5mm 11.5:1 piston?

Should it be very noticable?

[Mity Mo]

Unless your bike needs a piston change or you have any other reason for being inside the motor, it will not be worth the time and money for that swap. You might see 1-3hp but that would be alot. I would think it would be closer to 1 hp. Plus, I believe you would have to only use high octane race fuel or you would get spark knock. Plus with that change you also get a warmer running engine. Some things to think about........ Mo;)

[Tommy 17]

i have a good ?... what is spark knockin and detonation in the motor if u run 2 low of octane... i never been able to figure it out...

[VegasEx'r]

Pre-ignition (or pinging) happens when cylinder pressures &/or temps get too hot for the fuel, and it combusts before spark is delivered. The immediate impact is a loss of power & mileage, and the long term impact can be a shorter engine life. The higher the octane rating of a fuel, the slower it burns, therefore, the higher the CR of a motor, the higher the octane rating of the fuel needs to be to avoid pre-ignition.

This is also why there is no point in putting 108 octane fuel in a motor that has a 9.5:1 CR. The slower burning race fuel needs more compression to create power.

Hope that helps

[Wheelie]

I think you would see an approx 8% gain.