[Spridgets] 1275 vacuum advance

[lists]

You're all correct, some for 25%, others for 75%, and a very few of you to 0%.

The true story about vacuum advance:

Vacuum advance kicks in, when the engine is revving and the throttle is not fully open. The higher the revs (eginge breathes) and the more the throttle is closed (breathing is restricted) the more vacuum you have in your manifold, which results in more (up to a certain degree) spark advance.

Reason for that: The more vacuum you have in your manifold, the lower is the filling degree of your cylinders (because the engine can't breathe as much as it wants to). The lower the filling degree of your cylinders, the slower is the burn rate of the air/fuel mixture. The slower the burn rate of the air/fuel mixture, the more advance you need (because otherwise the pressure resulting from the burnt gases hits the piston too far down its way to its BDC).

Conclusion: Vacuum advance is very effective for the driver not putting the pedal to the metal. For the racer it will not come into effect.

Eric
www.brits-n-pieces.com
specialists for 123ignition