Turbo distributor

[Spruce]

Hi
Can some one explain the difference between US and Euro distributors (930/60 series engine)
Thanks

[PhatA55]

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[RarlyL8]

There are a few differences in the early 930s.
The factory repair manual references 4 different distributor specs per year. These are (1) ROW or Euro cars (2) Japan (3) USA and (4) California.
If you take the extremes, Euro vs California, you will see that the Euro has a more aggressive timing curve and only one vac port for retard when the throttle is cracked. The California (930/63) has 2 vac ports for emission use and a less aggressive timing curve.
There may be more differences, those are the ones I remember from dealing with the issue a few years back.

[NathanUK]

My euro '81 930 has two pods. Not the original engine. I doubt if it came from the US of A though.

The only movement I seemd to get from them was by sucking on the tubes. Blowing with my mouth didn't do much.

I would love to know what is what.

[PhatA55]

I've only got one can on my dizzy.

[RarlyL8]

Run the numbers on your distributor to see what year(s) it was used. It would not be unusual for the distributor, or any other part for that matter, to have been swapped out at some point in the engine's life.

The '78/9 units have a vacuum retard for emmission purposes. The California model has 2 vacuum ports that work in concert with the garbage can pile of CIS smog crap that the motor was burdened with. All ports are vacuum, that is why the dizzy only moves when you pull vacuum on the port. It is not a push-you pull-me setup. Pressure does nothing.

Is there something specific you are wanting to know about these units? The Euro distributor is (obviously) the best one for performance purposes but any of them can be modified to work the same way or better.

[PhatA55]

Brian, are you saying that the vacuum retard has no performance benefit, only emission reduction?

[NathanUK]

I think what Brian is saying is that when you blow into a pod nothing happens. I did this to my 930 and nothing happened. I did wonder if it was because of the low pressure from my mouth though and that maybe it would move at say .5 bar.

My engine is a 930/66.

[PhatA55]

I knew that blowing into it does nothing and sucking on it (that doesn't sound good ) retards it. I figured that out when I dismantled it to clean and lube it. I was just curious if the only reason is for the vacuum retard was for emission control or if there is a mechanical need for the retardation. My understanding is that while not in boost (vacuum on the canister is overpowering the springs in the dizzy) the timing is held in retard by the canister and when boost develops there is no longer a vacuum to hold the springs so due to their natural tension they return to their normal advanced postion. Is this correct?

[NathanUK]

I was going to ask you if you were sure that happens, but then when I read all of your post I see you were asking a question, not stating fact.

I really would like to know how this all works. I have a feeling that you have it wrong though.

I guess you could always check with a timing light what happens when you suck on it. Suck on it and see

[PhatA55]

As I remember, when I applied vacuum to the canister (sucked on it) the magnetic pickup turned counter-clockwise in the dizzy. The firing order is 1-6-2-4-3-5 going counter-clockwise. So, if the pickup blade was lined up with plug #1 with no vacuum, applying vacuum would move it closer to #6. This would cause the firing of the plug to be later than with vacuum applied. Wouldn't this be vacuum retard as Brian indicated earlier?

[RarlyL8]

You are correct, the vacuum pot(s) only retards the timing during off-boost events.
Contrary to popular belief, the '78/9 distributor does NOT retard timing under boost. You can blow on that bugger 'till your eyes pop out and it won't retard the timing.

[PhatA55]

Thanks Brian. That begs the question: if emissions were of no concern would it help, hurt, or make no difference to the engine if the vacuum retard were disabled? Does the engine require the timing retard for proper operation?

[Spruce]

In my case I removed the double chamber and replaced it with the single tube type as listed for the Euro distributor my problem is my mechanic is unsure if the distributor is different internally as the engine is ex California but has had all the emission gear removed.
Thanks for your replies

[PhatA55]

Does the double chamber canister allow advance AND retard reacting to both vacuum and pressure? If so I would wonder about the operation of the springs.

[fredmeister]

My 79 distributor has the vacuum retard side disconnected only, but the static intial timing at idle needs to be set at 10 degrees AFTC in order to prevent pinging. I think the original owner did this when all the emissions stuff "fell off"....how convenient.
Vacuum advance still functions.
Careful when messing around with this stuff as the turbo is extremely sensitive to detonation under boost, and total advance is a critical value.

[RarlyL8]

Advance is mechanical.
Retard is vacuum only.
Boost is not registered by the distributor.
The Euro single pot vacuum retard is not very agressive and is best left alone.
If you wish to maximise the timing curve you can mechanically block the retard function and set the timing at 28* total. The timing will come in as quickly as your block allows. Always back up your tuning with a dyno run or an LM-1. Boost and detonation do not mix.