Spinrique:
A distributor performs 3 functions:
- Triggers the coil. The distributors that came with pre 1980's Alfas did this with points & condensor. Newer distributors, aftermarket models sold by Centerline and others, as well as the 123, do this electronicly - using a photo-electric, hall effect, or magnetic trigger. In this area, the 123 is the same as other "electronic" distributors sold by Centerline et al.
- Sends the spark to the correct plug. All distributors handle this function the same way, using a rotor and cap. So, again, 123 is like the others.
- Changes the phase of the spark based on rpm - this function is called "advance", since the spark needs to lead the crankshaft by a greater amount as rpm increases. This is because the flame in the combustion chamber takes time to propagate, so when the engine goes faster, you need to light the fire sooner. In this area, the 123 differs from all other distributors that I am aware of. Other distributors perform this function mechanically, using springs and weights. The 123 does it with electronics, making it simpler to change the advance curve, and providing greater accuracy & consistency.
Cheez - I sound like a shill for 123! Note that I've never owned one, or even seen one. Still, it seems like a neat idea. Obviously a crankshaft-fired ignition has the potential to be even better, as you don't have timing inaccuracy due to slop in the crankshaft-oilpump gears. But, the 123 device is a lot simpler to install.
