Hi Folks,
I'll be brave and show my ignorance with these questions.
I'm trying to get a grasp of ignition timing so that I can understand it rather
than just follow directions in some manual.
I understand that the basic idea is. . . the spark needs to advance (happen
earlier) as engine speed increases, because it takes some time for the flame
front of the ignited mixture in the cylinder to expand. So when the piston is
zooming up towards the top faster, the spark needs to fire a little earlier.
And I understand that this is taken care of by the mechanical advance (springs
and weights) in the distributor.
What I don't understand is why there is a stop (an upper limit) for the
mechanical advance?
I mean . . . if you run the car up to 5000 or 6000 rpm, doesn't the same logic
still apply? You need to have the spark earlier to compensate for the faster
moving piston?
Secondly, I'd like to know about timing at idle.
Once again, I understand that if the spark happens too early (is advanced too
much) the air fuel mixture is going to be fully ignited and expanding BEFORE
the piston gets to the top of its stroke. It is easy to see why that's a bad
thing.
So . . . why would it be wrong to set the timing at idle by just slowly
rotating the distributor around and finding the spot where the idle is highest?
The thinking being that an earlier spark is going to work against the rising
piston and slow things down, and a later spark is sort of wasting energy.
What would happen if someone were to do this?
Would the engine ping like all heck under acceleration?
I know this is a simplistic view, and I'm probably missing something obvious
about the whole concept (heck, I'm not even looking at vacuum advance or
retard, (yet)) but I figured I'd use the knowledge of the list as a reference
rather than try and look it up somewhere.
(Guess I just showed that I'm ignorant AND lazy)
Thanks for your help.
Scott
1970 TR-6 Daily driver
It gets me to work, or I have to bum a ride from my wife. Gotta fix that TR-4
so I can have a back up vehicle.
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