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Distributor / Vacuum Advance Q .......

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George Zeck

George Zeck

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In process of upgrading many items and have purchased the Petronix Ele Ignition Upg (Neg Ground) (~ $65). The car is currently in many pieces at the moment and either me or PO broke the vacuum advance on the distributor.

I'm a bit blind on this -- but a friend suggested that I might not need this since I am going to be using the Petronix and figured many out there have installed / using this setup.

Before going and speding $$ on a replacement part that I might not need -- thought I'd try to find out if this was the case or not.

Do I need to use the vacuum advance when using the petronix ignitor I ??

Thanks tons !!

George Zeck
 
I believe you still will need to hookup the vacum advance. The instructions I got with mine did not indicate otherwise.
 
Hello George, I'm a Healey man, have a Healey 3000, but I was just surfing around and saw your post about Distributors. If you go into the Search mode on this site and search under 'vaccum advance' you will find some very informative discussion on your topic. A few years ago I did a buget rebuild of an MG Midgit 1275 engine for a young kid in the neighborhood. The vaccum advance was broken and he had no more money so I just plugged the vaccum line at the carb/manifold and he never new the difference. The vaccum advance is used primarily to help with throttle response at part throttle crusing speeds and to provide a little less gas consumption. But in most driving conditions you would never notice a difference with or without it. On deceleration, it tends to keep the timing advanced abit from what the centrifical advance would be holding it at and this just helps to smooth out the rpm transitions. /ubbthreads/images/graemlins/cheers.gif
Dave
 
Take a look at "MG Distributor Swap" currently on page 3. It has some good info and indications are you don't need the vacum. I am still learning things. Good to know that its not absolutely necessary. Please disregard my prior response, although the instructions with the Pertronic's doesn't mention to leave it off. Probally doesn't matter if you do or not.
 
Interesting - a quick look at Vizard's book, and he claims that it is wrong to not use vacuum advance for a street A series engine. I got a similar opinion from Rivergate (they built the engine I'm about to stuff into my Midget). My dizzy still has the vacuum advance working, so I'll keep using it.

The idea that the Pertronix would affect the need for vacuum, though - I don't think it changes anything. If you need the vacuum advance, you will still need it with Pertronix taking the place of the points (after all, the Pertronix basically is doing what the points were doing, right? In theory, at least, it shouldn't alter the timing).

JB
 
Hi George, the Pertronix installation doesn't duplicate the effects of the vacuum advance. I put one on my Midget and kept the vacuum advance. As far as how it behaves without the vacuum advance, I can't say I've tried that on mine, so I'd go with Vette's description.
-Dave
 
I have been running without a vacuum advance for over two years. You really don't need it! As Vette pointed out the vacuum advance just helps a little. Under high vacuum situations, i.e., starting off the line or backing off the throttle it will advance the distributor a little to help. Once you have "x" rpms the mechanical advance kicks in and basicly overrides the vacuum advance. My distributor has been modified (weaker springs) so that the mechanical advance starts working earlier. Also as Vette pointed out you will lose some gas milage but not that much.

Just out of curiousity what is broken on your vacuum advance that is not repairable?
 
On the "bell" shaped item on the end -- it split in 2 pieces. I am able to find a part, but since upgrading to the Petronix, was told might not need it so I didn't need to replace.

Not sure if I did this (falling off a shelf for example) or it was broken years ago and ran Ok w/o it. Upon disassembly of the engine compartment, the issue was discovered.
 
Hello all,
it depends on your driving style, if you have the throttle wide open a lot of the time the vacuum advance is redundant.
The other option is to tune the engine so that it doesn't need it, which will involve richening the low to mid range i.e. cruising part of the rev band.
Alec
 
Think I'll err on the side of cautionand pick one up. I'm not a racer (wide-open) so I think it probably wouldn't be a bad idea.

Tx-

George Zeck
/ubbthreads/images/graemlins/hammer.gif
 
George,
Another 'option' is find a used distribtor at a swap/parts meet that has a good vacuum advance unit. Take a piece of vacuum tubing with you to test the vacuum advance unit. You can safely run your car without it and the only downside will be a loss of 1 to 2 MPG!
 
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