Jim posted a nice reply to a gent this week who was asking what the maximum compression ratio is for a certain octane of pump gas. Jim states that there is no solid rule of thumb, then goes on with this very insightful paragraph...enyoy the subtleties!

"One of the best rules of thumb I've found is to include in any engine package the most efficient level of fuel atomization possible {MPFI is an example of this}, mixture motion that is intended to minimize air/fuel ratio extremes in the combustion space and cylinder-to-cylinder and and mixture proportions optimzed as possible. It not so much the failure of a fuel's octane level that leads to detonation as it is lean/rich conditions in the combustion space where the leaner mixture dominates, burn too quickly, raise peak cylinder pressures {pre-TDC on compression but after spark initiation}to inordinately high levels and cause the spontanenous breakdown of the propogated flame."

Jim's site is http://www.n2performance.com I think.

Regards.
BigMoose

 

I can't believe it. I understood that.

 

His articles are always really good.

He's always spoken pretty heavily on proper air:fuel mixture homogenization and intake charge quality (swirl and velocity).