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I think this has been a source of confusion in some instances.

In reading the manuals, on some cars you're instructed to set the timing at 4000 rpms (some with and some without the hoses connected), then check the timing at idle against the specs with hoses connected (to confirm the vac retard). Setting it at 4000 means twisting the dizzy to get the correct value. Checking at idle means just that...check to confirm it's correct. If it isn't correct at idle, then there is something wrong with your dizzy advance mechanism and you're recommended to have your dizzy checked out/repaired. If after going through setting at 4000 and it ends up not being correct at idle....and if you were to twist the dizzy again to correct the idle (since there is no other way to affect or adjust the action of the pot/can), then it will be off at 4000 rpm. Obviously the most important setting is your 4000 timing when all your mechanicall advance is in.

Make sense?
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Old 04-03-2010, 05:28 AM
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Quote:
Originally Posted by mark houghton View Post
I think this has been a source of confusion in some instances.

In reading the manuals, on some cars you're instructed to set the timing at 4000 rpms (some with and some without the hoses connected), then check the timing at idle against the specs with hoses connected (to confirm the vac retard). Setting it at 4000 means twisting the dizzy to get the correct value. Checking at idle means just that...check to confirm it's correct. If it isn't correct at idle, then there is something wrong with your dizzy advance mechanism and you're recommended to have your dizzy checked out/repaired. If after going through setting at 4000 and it ends up not being correct at idle....and if you were to twist the dizzy again to correct the idle (since there is no other way to affect or adjust the action of the pot/can), then it will be off at 4000 rpm. Obviously the most important setting is your 4000 timing when all your mechanicall advance is in.

Make sense?
That is exactly it. I wasn't as clear in my description. Set at 4000, check at idle. Edited the other post for clarity.
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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

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Last edited by equality72521; 04-03-2010 at 06:34 AM..
Old 04-03-2010, 06:16 AM
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It seems condensation can drip down the boost retard hose to the pressure pot. Thus, there is potential for it to rot out on that side at least. A long enough tube with a loop at the bottom might reduce that potential.

Checking operation buy verifying timing at idle as Mark notes would seem important.

But what about verifying 'boost retard' is working correctly.

This would require a hand pump. If the vac retard side (inner) is disconnected idle should increase. that by its self and also tells us vac retard is working.

Then adding pressure to the boost retard side (outer) with a hand pump sould retard and bring idle rpm back down. Better to observe at the timing mark.

Then there is the solenoid on the Vac-Ret side of the double pot dist. It would be good to be sure it is working correctly as this may be necessary to block vac-retard to ensure we get boost retard. (not verified)

As noted by Dave, these ignitions are getting pretty dated. Verifying that all functions work might be a good idea. Especially anything relating to boost timing.
Old 04-03-2010, 07:45 AM
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[QUOTE=911st;5274430] Then adding pressure to the boost retard side (outer) with a hand pump sould retard and bring idle rpm back down. Better to observe at the timing mark. Use a pump-up bulb from a blood pressure tester.

Then there is the solenoid on the Vac-Ret side of the double pot dist. Get rid of it....I don't have one and not really needed IMO. One less thing to worry about. QUOTE]
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Old 04-03-2010, 08:37 AM
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[QUOTE=mark houghton;5274496]
Quote:
Originally Posted by 911st View Post
Then adding pressure to the boost retard side (outer) with a hand pump sould retard and bring idle rpm back down. Better to observe at the timing mark. Use a pump-up bulb from a blood pressure tester.

Then there is the solenoid on the Vac-Ret side of the double pot dist. Get rid of it....I don't have one and not really needed IMO. One less thing to worry about. QUOTE]
I have to agree with you on removing the vacuum retard delay solenoid since installing the MSD boost retard box and advancing the static timing to around 12* BTDC at idle. You just don't need it anymore.

When the idle speed timing was at the weak stock setting of 0* or TDC then that vacuum solenoind delaying the vacuum retard signal to the distributor was a help to keep the idle speed up around 1100 rpms for the first 2 minutes after a cold start.

Now at 12* BTDC at idle and a cold start in Florida, the idle speed is about 1000rpms with only the help of the cold start air bypass valve because of the advanced timing making a stronger idle and then it drops down to 800 rpms when air bypass valve and engine warms up.

Now I'm using that vacuum solenoid with a summit racing RPM switch to delay the boost signal to the WUR. It's currently set to open the solenoid at 4500rpms with a K27 7006 turbo. Works great.
Old 04-03-2010, 09:15 AM
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After some 50 pages of ignition learning and discussion I still do not understand if the solenoid dose or dose not have importance when it comes to getting boost retard out of the dual connection pot.

If we get boost to both sides of the pot, do we get boost retard?

Or do we need the solenoid to block the Vac-Retard to ensure we get boost retard?

Thx.
Old 04-03-2010, 01:04 PM
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I didn't have much time today but I had a little. What I found is the pot is vacuum only, no pressure. When vacuum is applied with a pump the arm is pulled into the pot causing the spider ring (not sure what its called) to turn counter-clockwise. Remember, I have a left side mounted single pot. More to come.
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Old 04-03-2010, 01:13 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #107 (permalink)
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Quote:
Originally Posted by RarlyL8 View Post
The distributor function is very simple. Vac pulls down the timing at idle, mechanical advance operates during accelleration and the lack of vacuum prevents any further advancement or retard. The timing is mechanically locked down at 26* @4000rpm.
This indeed matches my observation.
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"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
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Old 04-03-2010, 01:23 PM
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Mark,

Works as expected then.

How much timing that can be run on boost safely depends on the car and conditions.

Again, the C2 Turbos run about -18 to -23 depending on intake air temps and US 930s run about -16 to -19. You might be able to run more under some situitions. As you do not have a boost retard function I would not exceed this much without good info to the contrary.

If me, I would add MSD with boost retard. Set timing at about 33-35 deg with vac line temporarily disconnected and set the MSD boost retard at about 1.1 to 1.3 deg per pound of boost and fine tune from there.

Or, convert to a US dist.

There is info that some are going more aggressively than this without issue.

Please verify above with a real expert.
Old 04-04-2010, 09:10 AM
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Quote:
Originally Posted by 911st View Post
... dual connection pot...do we need the solenoid to block the Vac-Retard to ensure we get boost retard?
Thx.
Anyone know for sure?
Old 04-04-2010, 09:13 AM
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I'm not sure. I wish someone with a stock system would check it. I know for sure that with pressure to both sides there is no retard.
Quote:

Quote de 911st



... dual connection pot...do we need the solenoid to block the Vac-Retard to ensure we get boost retard?

Thx.

Anyone know for sure?
Old 04-05-2010, 06:08 AM
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Quote:
Originally Posted by 911st View Post
After some 50 pages of ignition learning and discussion I still do not understand if the solenoid dose or dose not have importance when it comes to getting boost retard out of the dual connection pot.

If we get boost to both sides of the pot, do we get boost retard?

Or do we need the solenoid to block the Vac-Retard to ensure we get boost retard?

Thx.
That solenoid which is in-line with the vacuum retard line on the later dual pot cars...it just blocks the retard signal on cold start for perhaps a minute or so to help with establishing a higher idle. I believe it is then triggered through a time circuit which is part of the Lambda control system, and the valve opens to let vacuum retard the timing. As I said earlier, it really isn't needed. The AAR does a sufficient job of raising idle at cold starts in my opinion.

There is one more doo-dad (a thermal valve, non-electrical) that 's in line with the advance side of the pot. It's normally closed until about 150 degrees F, when it stays open. I believe its' function is to delay vacuum advance until the engine is somewhat warm - for emissions purposes. It, too, is most likely not needed and just another item to fail.

To answer to your question: No. I sure hope not anyway, or I've been running with 38 degrees advance on full boost all this time!!
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Old 04-05-2010, 10:55 AM
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I think you're 100% right Mark.

The little mechanical thermo valve down under the airflow meter housing is in the vacuum advance line to block vacuum advance when the motor is cold and during the early part of warmup so the timing is not advancing much and exhaust temperatures are therefor higher and heat up the catalytic converter on 1986 and later USA cars faster, making it do it's EPA thing sooner.

The centrifical advance is still working all the time and it has to or the car would be an unbearable slug below 3500rpms when cold.
Old 04-05-2010, 11:38 AM
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Good. I think that does it then. I have also found out that the vacuum electrical solenoid has to be energized to open. It is a normally closed valve. When it is cold, the temperature switch on the front, by the chain tensioner oil tubes tells the relay under the seat to leave the solenoid off.

Also, that explains how the boost retard works. The solenoid is off over 2200 RPM in all cases, which blocks pressure to the back side of the diaphram and lets the boost retard work.

Thanks911ST for starting all this. I think we've got it.
Old 04-05-2010, 01:54 PM
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Speedy,
The solenoid blocking pressure above 2200 rpm would indeed produce retard with pressure on the other side. Since I have no factory info that describes this solenoid, does a factory bulletin describe the block at 2200 rpm, or did you test this? If factory, this would certainly end the debate. Either way interesting point. Also is this a late US car you are talking about?
Eric
Old 04-05-2010, 07:05 PM
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A properly function system, whether the pot by its self or with the help of the solenoid blocking the Vac-Ret side, must retard on boost or it would not have been added to the dist.

There has been a couple of tests where if boost is put to both sides of the dist pot and it did not seem to create any retard.

One could run without the vac advance side hooked up. This would ensure the boost retard functions.

Testing the dist with pressure tee'd to both sides and or hooking a light bulb or volt meter to the solenoid and taking the car for a ride might help give us come confirmation.

Not sure if the solenoid is open with power or not.

To me this is the last outstanding piece of info as to how the dist works.
Old 04-06-2010, 06:40 AM
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My gut is telling my that my 87 US was designed to run at 26BTDC on .8 bar boost. However if this solenoid does indeed block the boost signal above 22 as Speedy says my thinking will change. Just find it hard to believe that the Porsche engineers are protecting this expensive motor with a cheap electrical solenoid, who's failure could result in a blown motor. Very interested in this detail.
Eric
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Old 04-06-2010, 08:08 AM
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You can always add a knock controller.
Old 04-06-2010, 10:07 AM
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Seems a dist that works with Vac advance would be a good way to go. If it failed it would most likely just not get full advance at cruse. Unless the 75-77's work that way none have Vac-Advance.
Old 04-06-2010, 12:28 PM
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Quote:
Originally Posted by e170drvr View Post
My gut is telling my that my 87 US was designed to run at 26BTDC on .8 bar boost. However if this solenoid does indeed block the boost signal above 22 as Speedy says my thinking will change. Just find it hard to believe that the Porsche engineers are protecting this expensive motor with a cheap electrical solenoid, who's failure could result in a blown motor. Very interested in this detail.
Eric
Agreed on that. And for all the people who have ripped out all emissions stuff except for the Lambda frequency valve behind the fuel head, all those cars would be toast right now if that little solenoid was so important for retarding ignition.

I'll say it once again: I am running with 38 degrees advance at no-load 4000 rpms. My MSD BTM retards 12 degreess of that by the time I'm on full boost, and I have to trust that the rest of the timing (another 8-10 degrees) is coming off as a function of the distributor pot boost retard.

I do not have that silly solenoid in-line, never have had it. My car has not melted a piston, nor does it cry the death rattle. This either means that the solenoid is not an integral part of the equation, or it means that I'm running with 26 degrees advance on boost with no problems. You be the judge, 'cause I don't know.

If I ever get a wild hair, I will attach various vacuum and pressurized air sources to my distributor and see what's really happening beyond conjecture....and will share the results if/when I do it. Until then, happy motoring!!!
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Old 04-06-2010, 02:09 PM
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