Re: [Chevelle-List] Advancing Timing

[Drippylimb]

Keith,
      Just a guess here, but even as low as 1500 RPM, the time it takes for a piston to go from 12 degrees BTDC to TDC has got to be milliseconds. So, if you fire it at say, 6 degrees BTDC, and figure the time it takes for the air/fuel mixture to fully ignite, there's a possibility that the piston may actually be on its way back down the cylinder bore before any power is applied, wasting some of the power stroke. Firing the plug earlier, at 12 degrees BTDC, gives you the time needed to fully ignite the charge while the piston is at or near the very beginning of the power stroke.
      Lets do the math.  1500 RPM equals 25 revolutions per second. That's 9000 degrees of travel every second. Assuming that a 350 mouse motor is a 4" stroke, ( I'm not sure ), 12 degrees BTDC equals roughly 1/8".  That's 10.8 milliseconds before TDC. And that's at a fast idle....imagine 4 or 5  thousand RPMs.
      OR, I could be way off base with these figures. I never thought about it before, and its the best answer I could come up with quickly. Take it easy, its nice outside.

           

Dan McIntosh     
65 Malibu