On a carb engine you got MAX load part load and idle, when it comes to spark advance, right?
So whats the need for all the cells on the EFI cars? Just a aid to keep the MPG down or to enhance preformance? Or both?

When I talk to carb users about the tuning involved on our cars they just shake there heads. And wounder if we ever got time to enjoy our cars hehe, they got a point i guess..

Thanks...

 

A non computer controlled dist. uses a vacuum can which senses load at fixed throttle and throttle position at a fixed load sorta. It uses weights and springs for rpm based advance. When graphed, both are a straight line.

Basically vacuum is applied to a spring loaded diaphragm which is attached to the mag pickup mounting plate in the dist. Move the plate, change the timinig. Anything that changes vacuum, will change timing. There is more to it.

Same as an EFI car. Except MAP and TPS, plus some other stuff is used to calculate the desired adder to the base.
You can do more with a computer and tables, so you get better emissions and performance.

As an example, when I started tuning my MSD vac. adv, I had to "map" how much the can gave me in total adv. Then what vac it started and finished at. Then I had to make my own limit plate and fit it to the dist. It will go in two ways which will alter the curve. It also limits the amt of total allow from the stock 15*. I could also change cans to alter the curve. Actually it's a line since it has a straight rate spring. Just the start and stop vac #'s change. There are also two vacuum sources. One only has vacuum at part throttle, the other is manifold vaccum.

How much work is it to change the adv in $8D?

Most people just disconnect the vac adv when it makes the engine rattle. .. monkeysee monkeydo,misconception, ignorant, lazy, whatever.

All the cells are required so you get an actual curve instead of a line. Look at the graph of a spark table. It does stuff you could never do mechanically.