[kleetuz]

I saw one of these on ebay, then I decided to read about them.

One of the features is that it can change the timing curve at different rates at certain rpm (Switchable), and it is made to work with distributor based ignition systems.

Another feature is that it has automatic start retard from 1 to 25 degrees.

I'm just a little confused about this because

1.) The distributor is turned by the cam

2.) The weights in the distributor change the angle relative to the shaft to advance the timing and control the rate of advance.

So How can a computer change the timing curve or advance at different RPM of a distributor, without physically altering its orientation relative to the drive? I could see some variation by really precise timing, but the rotor and cap only have so much room and time where contact is made for each spark.

I mean it's not physically moving the distributor shaft relative to the housing, - that is controlled by the fly-arms and the rpm they are spinning at and the springs attached to them.

So how is this possible? Seems you would need a mechanical linkage, that could move an arm, like the vacuum advance arm, where it is actually attatched to the plate.

Also, how can it retard the timing by 25 degrees for the same type of reasons.

I'm confused, I just don't see it.

 

[coolfalcon]

Its called micro processing. It will work best with a locked out distributor.

 

[kleetuz]

Well you can process a lot of information as fast as you want, but if my processor tells the coil to discharge voltage to the spark plug and there's no contact between the rotor and cap there won't be any energy getting to the plug, it just can't. This is where I don't see being able to control it so well.

So they process the engine rpm to time it just right to use that window where there is contact between the cap and rotor to send the voltage and slightly alter the timing?

If you are doing this, how can you get away with 25 degrees difference? If I want to make a 25 degree timing change its a pretty large rotation of the distributor housing relative to the drive.

 

[Neal]

My wild-a$$ed guess is that it comes down to the size of the contacts on the rotor and in the distributor cap. I don't think that those have to be perfectly lined up to complete the circuit. So the spark could pass between the contacts at any point from when the rotor's front tip first approaches the cap's contact to when the back tip reaches the very outside of the cap's contact.
Does that come to 25 degrees? Maybe...