Why does dieseling happen?

[Capri306]

Correct, tmoss & Ieatcamaros. The geometry of the combustion chamber has a lot to do with the proper spark timing for optimal combustion. However, I completely agree 16 degrees BTDC is way too much. He might even make more torque with ~12, but a chassis dynamometer is the only way to know for sure...which I highly recommend once major components like cylinder heads are changed.

Keep running 92-93 octane gasoline. The octane rating (in simple terms) is the ability of the fuel to resist detonation, which is NOT the same as combustion. You are not "dieseling," you are getting spark knock, plain and simple. So-called dieseling occurs at shutdown only on carbureted engines (or fuel injected ones if the circumstances are right), just to clarify. Anywho, just back the timing off, be sure your injectors, fuel pump, and fuel pressure are up to snuff, and you should be good to go.

BTW, have you done a spark plug reading yet? They're probably covered in aluminum bits by now, anyway, so you'd better replace them before making too many more high-speed passes.

[89fast5oh]

Whenever I set my timing I just get the engine to operating temp and go out on the hi-way, and put it in 5th gear and just keep turning the distributor till I get a bit of ping, then turn it down so it stops.