detonation

Retard the ignition timing
Burn higher octane fuel
Lower the engine temperature with a 160 thermostat
Run a "colder" spark plug
Lower the compression

"D" any/all the above depending upon how your engine was built.

I would look into water injection, A lot of turbo people do the DIY rout with agricultural high pressure pumps and have had great results.

Water injection can use straight water, or a water methanol mix, a lot of people just use windshield washer fluid.

http://www.dawesdevices.com/water.html

Jordon