Ive decided to go with a mallory unilight distrubuter to get rid of my old points system. But im having trouble deciding which route to take. I like the simple vacum advance plug and play but what benifits are there in going mechanical advance? How do you set up a mechanical advance? Im kind of lost when it comes to this.
All distributors have mechanical advance but not all distributors run vacuum advance. If yours is a street car you should be running vacuum advance IMHO. When running vacuum advance the choice is whether to run full manifold vacuum or ported vacuum to operate the vacuum advance mechanism. I have set my distributor up to operate properly running full manifold vacuum for best performance but on a stock or nearly stock engine ported vacuum is best.
I am not an expert by any means but I would be happy to elaborate if needed.
I'm running straight mechanical advance on two of my cars and they run just fine BUT they would get better gas mileage with vacuum advance on them.
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One thing I can tell you about the Mallory Uni-lite unit is Do Not leave the ign. key on for any length of time. I have that system on my 550 h.p. big block Chevelle mechanical advance and I accidentally left the key on and burned out the eye. A $95 mistake. I was recently told that you can buy some type of resistor to insall in line to prevent this from happening. Good luck with it. For my newer project of my recently purchased 65 Mustang fastback (With the help of a lot of VMFers ) I pulled out the Accel dual point dist. (which was also mechanical advance due to the radical cam) and went with the Pertronix 2 dist. and Flamethrower 45,000 volt coil drop in unit and am very happy with it. Good luck.
I don't recommend the Unilite. Just way too sensitive and replacements is really spendy. They are no more accurate than a magnetic pickup. The Mallory magnetic is a great dizzy and really tough. Get a vacuum advance unit. It will perform better, plus better milage.
You might take a look at the Pertronix brand dizzy. They are very well built and have a bearing at the upper shaft. I don't recommend the MSD units as they have dissimlar metals in the advance unit and corrode quickly amking the advance sluggish or not work at all.
Location: The woods of the Finger Lakes, western NY
Originally Posted by 02Lightning
How would you define manifold vacuum or ported vacuum? Manifold is obvious but what do you mean by Ported vacuum?
"Ported" = at or above the throttle butterflies
"Manifold" = below the throttle butterflies
Ported vacuum is a creature of the emissions monsters. IIRC, it's more effective at keeping N-oxides down while at or near idle, as it controls ignition more tightly in low-opening transition states. Somebody with a clue could probably explain it better than that.
I use ported vacuum on all of my cars. A big advantage is that you get a little boost of timing right off idle at throttle tip-in, this helps improve driveability and fuel mileage. I've tried a manifold vacuum setup several times and I just don't like the way it feels or drives.
You'll get the usual feedback of "vacuum advance is for smoggers" and every mutation of that statement you can think of. Simply put, if you have a stock or mildly warmed over engine, then you're just wasting a whole lot of fuel if you don't use vacuum advance.
My ignition setup of choice for a street cars is a Ford Duraspark dizzy with an MSD box and coil. Dead nuts reliable and if the dizzy goes bad, parts are as close as your local auto parts store.
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Originally Posted by TommyK
It says "author unknown" but it was written by Lars Grimsrud.
I thought it looked kinda familiar. Lars and John Hinkley (aka John Z), both Corvette guys, have written a whole series of articles on engine topics (particularly ignition) that are really textbook quality. John is a retired engineer from Chevrolet, and I believe that Lars background is similar.
This brings up something else I have put off. I have both a MSD dist and several Ford distributors. I have been running a Ford because someone spent a lot of money getting it set up right for the motor it came with (I still run it). When ever I try to hook up the vacuum advance the engine dies. I have tried several distributors (I have a box full) and its always the same thing. I tried every port on my 4150 and my intake manifold they are all the same. So I run without vacuum advance. I would love to hook it up if someone understands what I'm doing wrong. Wouldn't mind a little better gas milage...
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