Hey team
A bit of theory on distributors for anyone who might be wondering. The ability of the breaker plate (the plate the ign points are screwed onto) to move relative to the distributor housing via the vacuum servo is how the dizzy modulates ign timing wrt engine LOAD. The ability of the cam that opens and closes the ignition points to move relative to the dizzy drive shaft is how the dizzy modulates ign timing wrt engine SPEED. The load side of the timing 'map' is there to advance timing when the cylinders are not filling as efficiently, which is when we're cruising at highway speeds, with lots of manifold vacuum (ie only part throttle opening)...this is essential to achieving good fuel consumption. The speed side of the timing map is there to advance timing as the engine speed increases, and there is less time for the fuel charge to burn...this is essential to increasing power as the engine speed increases, so that maximum cylinder pressure is being achieved throughout the power stroke.
To disable the load side of the dizzy will mostly affect everyday driveability and especially fuel consumption. To disable the speed side of the dizzy will mostly affect driveability and power.
While you can fiddle around with a timing light in your back yard and all that, it is impossible to set a dizzy up properly in a car without a dyno to load up the engine, and effectively superimpose the effects of load and speed on the distributor to understand what the timing is across the engine operating range. This is a job best done by an auto electrician/engine man who has a distributor test bench...they mount the dizzy on the bench, which can run through the full speed range while applying vacuum as well, and therefore work up the whole picture for you. They will mess around with spring tensions, advance weights to get not only the total advance where you want it, but also develop the curve between the setting at idle thru to full power. This is driven by compression settings, cam timing/profile, exhaust and carburettion etc.
The very best set up is to go to someone who has a chassis dyno and a dizzy bench, and they will get the whole thing setup to give max power thru the rev range, good driveability and good cruise/fuel consumption as well. You can then decide which of these you want to compromise on depending on what you're using the car for.
CHeers
Jamo
