the main thing is to take a dremel tool and remove any sharp edges on the piston donuts and the edges of the combustion chamber. this reduces the hot edges from being hot enough to ignite the fuel mixture before the spark does.  One thing for sure. if you were to take the pistons to a machine shop and have them mill the donuts off that would remove the chances of that and would keep the compression low enough you could run 87 octane and still have a better than stock. much better I think because you would have a 2.4L 20R