[gtofreek]

Originally Posted by Nicks67GTO

Paul, why did you decide to angle mill? I was always under the impression that was a SBC thing and wasn't necessary on a Pontiac? Is there an advantage to angle milling?

It had nothing to do with SB Chevy's. I angle milled it because I want the sparkplug closer to the piston, so the chamber is shallower, and give the engine less tendency to detonate. Most people think detonation occurs from a hot spot in the chamber. But it doesn't. Hot spots cause pre-ignition which happens during the intake stroke, when the piston is near BDC. If a hot spot lights off the in coming fuel, it starts burning, and as the piston starts back up the cylinder and try's to compress that burning mixture, the pressure that develops is so high, it will melt and blow a hole right through the top of the piston. Pre-ignition destroys an engine in milliseconds.

Detonation occurs when the sparkplug fires the mixture, but the mixture doesn't get completely burned before max cylinder pressure occurs, Then, what ever air/fuel is left over, detonates from the pressure. Engines can survive detonation for quite some time. Engines don't survive pre-ignition. So by getting the sparkplug closer to the piston, and making the chamber shallower, should get the fuel burned quicker[less area to complete the burn in] so there is none, to very little unburned fuel left to detonate. By angle milling these, I got the sparkplug .080" closer to the piston.