The ports the two vac/boost connections are made to are a version of a "ported" connection.

The boost-retard connection is just outside the leading edge of the throttle butterfly so it dose not see boost at idle which is possible (I pulled about .2 bar at idle.) When the throttle is opened this port moves to a point past the butterfly and it sees the intake and sees the same vacuum or boost the motor sees.

The Vac-retard connection sits just inside the other end of the butterfly. At idle it sees vacuum. Once the throttle is advanced it moves outside the butterfly and sees the same pressure that one would see at the inter-cooler exit tank.

Thus, past idle, there will be no vacuum on the Vac-retard side and at cruse it will actually see boost.

At cruse the boost-retard side will see significant vacuum. With WOT when the intake manifold shifts to positive pressure it will see it.

Idle: vac on inside port, boost on outside port.

Cruse: Boost on inside port, vac on outside port.

WOT: Boost on both ports. --- This is why we need the solinoid to close. If we see boost on both sides, there will be no boost retard as proven above with the teeing to both sides of the pot and adding pressure.

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With the single port Euro it only has Vaccum-Advance. It is hooked up to a port that sees no vaccum at idle (we do not need advance there) and on curse it will se vaccum. With acceleration the vaccum goes away and the vac-advance is pulled back to a safe level for running on boost.

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I am very interested if there is more than 10 deg of retard past .8 bar. I was expecting a stop as 365-930 found he got full retard with 5 lbs of pressure.

On the first higher flow fuel head were I cam up with using a MSD rpm switch to delay enrichment, Brent used one of those solenoids that was left over to pinch off the signel to the WUR so he would not go pig rich.

Thus, I am not expecting it to be pulse on /off valve. I will try to check if it was the air pump or Vac-retard solenoid that was used and if it was open or closed with current. I do not know if there is difference between those two valves or not. Again, I am an idea guy.

I checked mine again, and it definitely does not hold pressure or vacuum on the back side diaphram connection using the mityvac. But if I hook it to engine vacuum it does. The engine can more than make up for the vacuum "leak". I would assume the same would be true under boost.

The reason I think a bleed must be required is that, if you close the solenoid under pressure or vacuum, won't it just trap the pressure or vacuum in the hose and diaphram if there is no bleed? What would be the point in that? You would just seal vacuum or pressure in. I think the solenoid must cut off boost to the back side so that retard can occur, so I think there must be a bleed.

As far as those who have taken their solenoid off, if you leave the hose on the back side off, then you get retard sooner than you want it. If you leave the hose on the back side on, and connect directly to the original port on the throttlebody, you get more retard at idle, and no boost retard. I don't think it will knock in all cases, maybe not at all if you can get 94 (r+m/2) octane fuel.

What year is your car? What are the numbers on the distributor? and is your car USA or ROW?
Also which vacuum pot connection are you referring to when you say "back side", the red hose to the left or the blue hose to the right?

My distributor is fairly low mileage, I mentioned the numbers on it in an earlier post. I believe it is in good condition and working correctly.

And both sides of the vacuum pot on my distributor hold vacuum with a new mighty vac hooked up to it directly on one port at a time... no leakage at all.
Maybe yours is a different model or maybe yours has a leak.

I just drove mine a little with the blue vacuum retard line disconnected and it idles about 300rpms higher and does seem a little peppier under 3000rpm. Then I stopped and put the blue vacuum retard line back on, burning my hand on the fan housing in the process and drove some more and it seemed to loose a little pep under 3000rpm.
I was on city streets and never really got into boost.

I'd like to just leave the blue vacuum retard line off and lower the idle speed at the throttle body down to 800rpm where I like it but then I don't know what the timing will be under boost and I don't want to take a chance on breaking piston rings or whatever with detonation.

If we were talking about fluid it would be a real issue. With air, the trapped air will compress. Especially if you add the volume of the supply tube.

It might even be possible the solenoid can be pushed past or closes with vacuum on the back side. Just thinking out loud.

That is preferable to having equal boost on the back side.

Maybe this slows down the retard a little. Remember, 930-356 found that he got full retard of about 10 deg with only 5 lbs of boost.

When Brent 930 sent his distributor to Andial my understanding was they told him to leave the back side / Vac-Ret side unhooked.

We have two reports today that with the Vac-removed we see a little bit snappier acceleration. This might indicate that there is potential on the off idle portion.

We are only removing the Vac-retard part and not really advancing the off idle part.

JF: Your description makes the most sense to me... My car goes into the shop to have the "vaccuum pot" changed next week [while i'm on vacation]. Hopefully, by then, we can come to some sort of solution as to what [and how] the heck the vaccuum solenoid does and works! Right now, my soleniod is disconnected...

On a side note: It's amazing how something so simple and "assumed" can turn out to be "not so!!"

Mooney,

Please get the take off and cut it open or send it to someone that can so we can see what is inside?

That would be major.

Thx.

This dose not directly relate however, I came across it and it dramatizes how different builds will be able to handle different boost depending on inter-cooler efficiency.

We have the same issue on the ignition side. It will depend on the AFR's being run, inter-cooler efficiency, cam, C/R...

Thus, a "dyno tune" is going to get the most from our motors. Still, we need to build in a safety margin as these motors do not have knock sensing or the ability to adjust ignition or fuel.

will do... I'll get back on this when i return [after the 14th]

One source seems to think the Solenoids are Normally-Closed.

Maybe just try to blow or such through one with the key off.

If this is so, it would see voltage at idle when warm to close it.

We still need to verify this.

My part number is the same as yours 0237302045 and the other number is PGFUD6. I was referring to the blue hose, so maybe mine and copterdude's are broken.

If someone can tell me where to get another one, I'll cut this sucker open right now, unless it costs $500 or something!

Piston, not diaphragm???

Looking at a dual connection pot, I am wondering if they might have a piston in them instead of a diaphragm?

10 deg of range is more than most Vac-Advance pots that use a diaphragm I suspect usually have.

If there is a piston it might be shaped like a cup and thus be directional.

Then with boost from one direction and vacuum from the other, it would better seal when working.

If this is the case and we put pressure on it from the vac side, such pressure might push past the side-seal of the piston. Same thing if vac is put on the boost side.

This might explain some of the differances in findings on some of the tests.

The dual port pot dose not have the seam on the side like a normal Vac-advance pot where the diaphragm might reside. It has a barrel to it and a recess where a spring would set if you wanted it to push inside a piston cup.

Just a thought???

No, I have seen the inside. There are two diaphragms. One is like a disk, and the other is like an annulus, and there are two springs, and two sets of stops. One set limits the minimum and maximum that the red hose side can move, and the other makes it so the blue hose side can only retard, not advance.

I have one. I will have to dig around for it. it had a broken vac retard port so I found another one. Will disect it and report.

I tested voltage at the female also and just turning key on , not starting, read battery voltage for a min or so then 0. I will put it all back together and play more.
This is getting expensive, a vacuum advance, and solenoid. The MSD 6530 is now a clear option. It's fully programmable, incorporates the 6420 and the 8977 into one package. Then I can get rid of it all.

Copterdude.

Great info.

So the solenoid is powered during cold start which means it must be normally-open and closes with power.

A programmable MSD that gets fully mapped ignition is probably a best practices set up! Has the potential to make improvements on many levels. Would be great if it had a temp sensor input. Most modern EFI set up I believe pull back timing with intake air temp.

Copter, are you in need of a vacuum pot? I found my old one, I believe it is functional, if you can figure out how to attach a line to the inner nipple as it is broken off and the PO I guess tried to JB weld it back on. I don't know if it would be of any use to you, but I will send it to you if you need it. I know first-hand that they are expensive. Just a thought before I crack it open in "the name of science".
Eric

According to the little symbol in the workshop manual it is a solenoid valve with three ports and two positions. When the solenoid is unpowered, the vent port to the atmosphere is blocked, and flow can go through the valve from port 1 to port 3 (unpowered = open). When powered, the port labeled "3" goes to port 2 (atmosphere). It does not show latching, so it has to be powered all the time to vent. The vent also explains how the blue hose side of the diaphram is bled down, so that makes sense, and further convinces me that copterdude and I have broken diaphrams on the blue hose side.

Can the ring change the pressure ratio from side to side so the boost side can overwhelm the vacuum side should it see an equal boost signal on both sides?

That is, if we have two pistons pushing against each other. One has twice the surface area and both get the same pressure, the larger piston will dominate.