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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269

Please be cautious with the info you are receiving here from me an others.

It is my belief that the early single connection 930 distributors do not have a Boost-Retard function. It has a 'Vacuum-Advance' function..

To check this run your motor up to 4000rpm with it hooked up and set timing to -29 deg. Then remove the vac line to the dist and run it up to 4000rpm again. If you timing is closer to -19 deg, it is a Vacuum-Advance pot.

When you go into boost, the vacuum advance function then goes away and your timing is pulled back to a safe level (in the -16 to -21 range).

If I am correct, and I can be mistaken on this, if you were to try running with this disconnected and set at -24 to -29, you will not get any boost retard on boost and be at risk of damaging your motor.

If it is a Vacuum-Advance pot as I suspect, it should be attached to the throttle body in a way that you do not have any vacuum to the distributor at idle. This way there will be no advance at idle. However, above idle you will get vacuum. You could put a vacuum gauge on the line to the distributor and verify this as another check.

You could also hook a hand pump to the pot. Put a timing light on it at idle. Try putting boost or vacuum to the pot and watch what the timing dose. If timing advances as I suspect with vacuum it is a vac-advance pot and should function as I believe. If it retards with pressure (boost) is has a boost retard function.

Originally Posted by equality72521 View Post
I've searched but I'm still confused. I have a euro single pot distributor that I understand to be vacuum retard at idle/low rpm and mechanical advance above 4000 rpm. Does this pot have any other use throughout the rpm range? Does it serve any other purpose on a turbo engine? Is there an advantage/disadvantage to disconnecting it?

Last edited by 911st; 03-30-2010 at 08:47 AM..
Old 03-30-2010, 08:42 AM
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