10.25:1 pistons- what octane rating would you suggest?

The short version is that there are just to many variables to take into consideration to tell what octane fuel an engine will require, static compression ratio really don't have much to do with it. You can build a 14:1 motor that will run on 87 octane or a 10:1 motor that requires 94 to avoid pinging.
Cooling, intake air temp, % of cylinder filling, cam timing, ignition timing, spark plugs, combustion chamber design, plus a lot more, all have an effect on the required octane of the fuel.

The only practical answer is use the lowest octane rating that your motor will tolerate without pinging, trial and error

steell wrote:

The short version is that there are just to many variables to take into consideration to tell what octane fuel an engine will require, static compression ratio really don't have much to do with it. You can build a 14:1 motor that will run on 87 octane or a 10:1 motor that requires 94 to avoid pinging.
Cooling, intake air temp, % of cylinder filling, cam timing, ignition timing, spark plugs, combustion chamber design, plus a lot more, all have an effect on the required octane of the fuel.

The only practical answer is use the lowest octane rating that your motor will tolerate without pinging, trial and error

yep.

agawam wrote:

timing and camshaft duration, not nessesarily compression ratio would be cause for higher octane fuel, the higher the octane the slower the fuel burns,if you had advanced the cams, timing or lenthend the ignition advance more octane would be needed, bikes with short runner intakes deliver a good a/f mixture so uping the octane isn't always nessesary, if you went to 12.5 then maybe

Do you have a reference for the bit about lower octane fuel combusting at a greater rate than higher octane fuel? Thanks. -Duck

Burn speed and octane rating are not directly linked. Although some higher octane fuels burn slower this is not always the case. The burn speed is actually a result of the chemical composition, percentage of aromatics etc, and while this is also responsible for the octane rating there are some race fuels around that have high octane AND high burn speed.

Here's a link www.aaoil.co.uk/tech_tips.cfm/type/fuels

zRider, it sounds like your motor is timed at the fire mark. I just backed mine way down after i installed the 1015cc kit. If i ran it at the fire mark it would need more octane. Im thinking that the energy levels are the same here. I dont like riding at 70mph, feeling the vibration of detonation and having a very narrow power band. So back down buddy! lol.