Generally, how do you know when you advance the initial to much?
answer; When the engine detonates under load.
Here's my 2cents;
Your "initial timing" needs to satisfy idle requirements and that is all.
Your Power timing is just that. From stall to about 3600rpm, your centrifugal timing has to satisfy the first rule; give it as much timing as she wants at WOT, until it detonates then subtract 2 or 3 degrees for a safety margin.
Now; by these two, your timing is correct under exactly two conditions; namely idle, and WOT.
Under the thousands to millions of other conditions your engine could be operating under,at any one time, all other timing is wrong; dead wrong.
That is where the vacuum advance comes in. It tries to bridge the gap.
Here is a test; rev your engine up in Neutral to about 2000rpm and set it on a fast idle step. Now reach in and start advancing the timing, and simultaneously readjusting the rpm to maintain the 2000 rpm. Just keep cranking and readjusting to 2000. When the rpm fails to increase with more timing, stop. Now read the timing. I bet you find a number over 50*. maybe over 55*. Maybe approaching 60*. Back the D up, and flip the engine back to idle.
So what did you discover? I'll tell you: under no load conditions at 2000 rpm, your engine likes way more timing than you imagined, am I right?
But if you had tried to drive it like that, it would not have taken much throttle to begin the death-rattle of detonation.
Between stall and about 3600rpm, your engine is very load sensitive. After 3600 not so much. So from stall to 3600, you the tuner have to satisfy the engines timing requirements for not just WOT, but the thousands of other in-between throttle and load settings.
Just reaching in and cranking the D to some arbitrary number that somehow satisfies your azzdyno is an exercise in foolishness.
What is the purpose of changing ignition timing?
Answer; to cause peak cylinder pressure to occur at a specific time (measured in crankshaft degrees), that provides the optimum energy transfer from the hot expanding gasses to the spinning crankshaft throws. Your optimum window is very small.
It takes time for the pressure to build , in the chamber, and as the rpm rises there is less and less time to get it done, so we have to start the fire ever sooner. Until somewhere between about 3200 and 3600 where this phenomenon stabilizes, and no more advance is required. This is under full load and full power.
But when NOT under full load NOR under full power the parameters change.
For instance; at idle, very few oxygen molecules actually find their way into the chambers when the intake valve is open. And of course, when they get into the chambers, they tend to space themselves apart to fill the entire cylinder. And the gas is not that crazy about it but in the best of situations it too spreads out. Now, as the piston comes up, it squeezes all those molecules ever closer together, but at idle, there are so few of them that it takes a long time for them to all find each other. And so sometimes, if you don't start the fire soon enough, some of those gas molecules often the biggest clumps,never do find oxygen to react with, and they go right out the tailpipe. Or maybe they finally find oxygen in the exhaust system, and burn there.So now you know why your engine likes so much advance at idle.
Your job, as a tuner, is to make it easier for the gas and the oxygen to find each other once in the cylinder.Well once the engine is built, you are sorta stuck with what you have.
If you have a carburator, you run into another road block which is the transfer-slot exposure underneath the primary throttle blades. That exposure has to be set over a very narrow range to baseline your idle fuel delivery, and your tip-in response. If you set the idle timing too far advanced, then to keep the rpm down, you have to reduce the throttle opening, which destroys the transfer slot fuel delivery. You can compensate for that somewhat with the mixture screws, and so you can make it idle. But now with the transfers drying up, you get tip-in issues and hesitations, sags or outright bogs. So you blame it on the accelerator pump, or worse the mainjet and spend unnecessary time working thru those systems, cuz all the engine wants is a tad more transfer slot fuel. But some guys get stuck thinking they have to have racecar timing on their street cars and so end up tuning for 20 to even 30 degrees of idle timing, (if they are tuning with a vacuum gauge). Don't be one of those guys. After the Transfer synchronization is set,your engine doesn't care about idle timing. Don't waste time looking for in the 20s when 12* is lots. Or 10 or 14 or whatever it ends up being to satisfy the Transfer slot exposure and a reasonable idle speed.
After that the mechanical timing is set for WOT conditions between stall and 3600.
And then the V-can does the rest. And very often, the Power Timing has to be sacrificed to satisfy the Part throttle timing.
Your azzdyno will never feel the difference of 2 or 3 degrees short of perfect power timing below 3600rpm, so don't waist an entire summer looking for it.
. The car go's really well for a amateur street car im just trying to optimize as i go
