Question ive wanted to know for ages

[Mr bayce]

OK you know how the dizzy's advanced is controlled by vacuum in the intake manifold as well as the centrifugal weights inside it?

I thought when the throttle is closed, there IS vacuum and at full throttle there is NO vacuum. wouldnt that make it advance at idle??

OR,

is it advanced when the engine is stopped? and when idling (under vacuum), does it get pulled back to the normal pos? therefore at full-throttle (no vacuum) make the dizzy return to advance?? get whet i mean? hmm

and does the same go for wastegates?

[Ben Wight]

There are two reasons you would want to advance the ignition timing of an engine.

It takes a set amount of time for the combustion process to occur, so as the engine rpm increses, its made to occur sooner and sooner. This is why distributers have mechanical centrifugal advance. The faster they spin, the more advance they deliver.

Also, when engines are under heavy load, and they are offered more ignition advance than what the mechanical advance offers, they will detonate. However, when an engine is under light load, they can handle more advance. This extra advance creates both more torque, making it more efficient, and a smoother idle when idling. I cant remember how it affects emissions.

When the engine is idling, or under light load like whilst cruising, then vacuum advance delivers a bit extra on top of the mechanical advance, which the engine can handle.

When under heavy load, like when the accelerator is floored, the vacuum drops to zero, and the only advance is delivered by the mechanical device.

Ben Wight