Re: BigKev's 1954 Packard Clipper Deluxe Sedan

Posted by BH On 2010/10/16 19:55:34

Not formally schooled in automotive technologies, I've heard and seen distributor vacuum advance function and effect described a few different ways. Yet, the more I try to find the definitive answer, the more confused I get as to what is correct.

If the burning rate of the air/fuel mixture is a constant, as engine speed increases, spark must occur sooner. Too late and the expanding gas of combustion will be wasted on the downstroke of the piston = loss of torque/power. Too soon and it actually works against piston travel = detonation/ping.

What I do know from practical experience is that a leaky vac advance diaphragm is often overlooked, and the engine is tuned around that problem, at idle. However, when you give it some throttle, the engine stumbles. Perhaps this is due to a combination of a lack of timing advance and a leaner air/fuel mixture - both due to a vacuum leak in the vac advance diaphragm.