[gtofreek]

Originally Posted by Blued and Painted

Those are good 1/4 times for the 2.56 gear. Must have quite the top end charge.
What cam with the hi compression iron head 455.

Run on is pretty common. The question for me is, does detonation occure before or after the normal idle ignition timing.

Detonation and pre-ignition are two totally separate things. Detonation occurs after the spark when all the fuel has not been burned by the time max cylinder pressure is reached[usually around 14° ATDC]. At that point, if the octane is too low, whatever un-burned fuel that is left in the chamber, detonates from the pressure, much light a bomb. The trick is too burn all the fuel before max cylinder pressure occurs. If you can do that, then you will not have detonation. This is where small, shallow fast burn chambers really help. Big chambers take more time to burn all the fuel. Detonation starts in the farthest points of the chamber from the spark plug. Usually on the other side of the exhaust valve.

Pre-ignition occurs during the intake stroke, long before ignition. If there is a really hot spot in the chamber, it can light off the a/f mixture as it enters the chamber, while the piston is on it's way down the cylinder. Now, with the a/f burning, the piston starts it's way up the cylinder, compressing the a/f while it's burning. Now the heat and pressure becomes so extreme that it melts the top of the piston, and the pressure blows a hole in it. If an engine pre-ignites, it won't run more that a few revolutions before the piston melts down. This can occur in less than a second. Think about this, at 2000 rpm, the piston is dealing with combustion over 16 times per second.