vacumm, mechanical, points???

[vintage_car]

I read about vacumm advance, and mechanical advance and points on a distributor. I think I know what each look like, but a picture of each would be great. What coils are best to use with each for optimum output and is one system better than the other? Maybe silly questions, but I'm just confused on it.

[BimmerSooner]

Not a silly question....I'd like to know too.

And what about electronic ignition systems? Better? What's the best whole-system electrical set-up for maximum performance?

[brad_c-ville_VA]

i don't have a picture handy, but the easiest way to tell a mechanical dizzy from a vacuum is to see if there is a hose running to a sort of saucer-shaped contraption on the side of the diz housing. if you have the hose and the saucer thing, you've got a vacuum dizzy. the mechanical advance units don't have the vacuum line and you can see the advancing mechanism if you take the mounting plate (the plate the points mount to under the cap and rotor). looks like a spring loaded whirly gig.

there are varying opinions on the use of both. some say a mech. dizzy is better for modded engines with higher comp. ratios and that vacuum versions give a better, smoother advance curve. i've used both in my modified engine and haven't seen a tremendous difference.

[vintage_car]

Is an electronic ignition system different than a mechanical distributor with a blue coil? Or is that a type of electronic ignition system?

[cyclopticgaze]

I asked about my distributor recently and it turns out it's a mechanical advance. Click here for the thread. Picture included.

[Beaner7102]

The Mechanical advance dizzy were fitted to Ti and Tii models, for two reasons 1. the Tii FI needed a quick timing advance to stop it pinking 2. no good vac ports on either the Ti or Tii.

The Vac advance dizzy was fitted to all Down Draft carb models.

The difference in advance is the vac advance acts slower (over a longer rev range) but gives a greater degree of advance, over the mech advance. But the mech advance is more reliable.

The electronic ignition on these cars is only an electronic points replacement (Pertronix, Crane etc). They are better as they can handle a more powerful spark (no points to burn) and should therefore be used with a better coil (e.g. Bosch black or red). You can also open the plug gap to about .035-.040 as the bigger spark can easily jump the bigger gap and give a more complete burn.

Hope this helps. Beaner7102

[brad_c-ville_VA]

an electronic ignition system has to do with how your dizzy fires off the juice to your plugs. in a stock 02 dizzy you have contact points that open and close via a eccentric cam located on the dizzy shaft. the cam is timed such that every 90 degrees of rotation of the dizzy shaft, an electrical connection is made, send from the coil through the dizzy to one of the spark plugs. (this is a very simplified explanation). of course all of this sparking has to be done in the correct order, at the correct time or you get an engine that doesn't start.

an electronic ignition relies not on contact points but rather spinning magnets at located on the dizzy shaft and electronic pick-up module (a hall-effect sensor) or a spinning disk with holes in it on the dizzy shaft and a photo-electric sensor that can sense the holes in the disc. like the contact points, the magnets or holes are located at 90 degree angles around the dizzy shaft and correlate to the positions that will align to send the spark on its merry way to the correct plug. check out www.howstuffworks.com for a good explanation of automotive ignition systems.

so basically, an electronic ignition system tells your distributor when to fire off sparks to the plugs. but, unlike contact points, the electronic ignitions have no consumable parts and don't rely on physical contact to time the electrical pulse. contact points work well enough, but can eventually corrode and wear down to the point where no contact occurs and you have no spark getting to your plugs. that is why all the old skoolers around here still carry spare contact points with them in their tool kits.

you can us a vacuum dizzy or a mechanical dizzy with an electronic ignition system with no problems. the pertronix electronic ignition system is a hall effect sensor (spinning magnets) system that fits neatly into the stock dizzy housing. other systems, like the crame xr700, are photo-electric sensors and require an exterior control unit about the size of your wallet to be mounted somewhere under the hood. i've used both and they are each typically reliable in my experience.

there are tons of useful resources on the net for contact point, pertronix and crane systems. all are are used or fitted on many, many vintage cars. i've learned most of what i know, which is a fraction of what manyof the 02 guys know, by reading and asking questions.

good luck,

brad.