What fuel to stop detonation with high compression help please

I am putting together a wr400, 444cc big bore with 13.5:1 hc piston.

I was hoping to run 98RON fuel.

How do i find out what fuel to run. I know if it pings to run higher octane, but how do i determine the correct fuel.

I can get higher octane but its expensive and not available at the pump.

Can i run 50/50 pump and race fuel? Can i use an octane booster? Is there any fuel i cannot run Eg. Methanol, ethanol etc.

There is a 10% ethanol mix available at some pumps thats called 100 octane.

I live in Australia so im talking RON ratings.

I want to know how to test my new engine safely to find the right fuel, and know what additives work.

Hopefully 98ron will be ok but if its not i can get up to 106ron for $$$.

Does any changes require jetting/fuel system changes.

Thanks for the help and only answer if you have credible knowledge.

Race fuel mix is the most common solution

You mix to the minimum amount of race fuel to eliminate detonation

13:5 is a substantial increase, so 50/50 should be expected

Ocatne boosters are typically just Toluene: not a very good fuel source on it's own.

For more detailed info, you should contact the Piston company


and I woundnt experiment with fuel/ combustion ratio's etc..

98 should/ could work fine,

but if not, use a booster, make sure "other" fuels dont "eat" rubber/ plastics...

98 RON should be more than enough.  In fact, the originally required 95 RON should be adequate.  Here in the states, gas pumps are all labeled with "AKI" ( anti-knock index), which is an average of RON and MON, and most pump premium is labeled 91-92.  This is roughly equivalent to 95-96 RON, and generally works out as being enough for most people running 13.5:1 with no other additives.  I wouldn't worry about it too much.

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