Note the "electrical on/off valve" that is plumbed on the Advance-Retard side of the dist Pot.


http://forums.pelicanparts.com/uploa...1248143722.jpg

This sounds like it might be an important lead.

Brian,

Again, how can this help us?

Please, explain further.

Is there somthing here we can use?

Thank you for your help.

pm sent.

One of the things I plan to offer more of as business grows is fuel and ignition tuning. I do this now on a limited bassis as it is time consuming. I am gathering CIS equipment to make a test bench and will do the same with the ignition. For many reasons it is an advantage to be able to make these adjustments without having the car in front of you. If you know how the car is set up you can dial these systems in pretty good on the bench.
Locking the distributor is just that. Same actions as we used back in the day when re-curving distributors in our V8 hotrods. The distributors are the same, just play with springs and advance/retard controls until you get what you want. With modern electronics you can go further and add electronic inputs from other areas.

Keith... I really wish you still had one of these cars so you could spend lots of money and time experimenting with it and try out all your theories.

Brian.

I did not understand "locking" and "applying our own timing curve" used together.

If one was going to build a race turbo one could probably just lock the dist at the peak boost value and bump the idle a bit and get by. For us on a street car that would not be a step forward.

Was hoping you had some of those "tuner secrets" we could use".

Again, thanks for the input.

The best. :)

Been there, done that, twice (78 euro & 91) and miss em so hoping to do another someday in the not to distant future.

I just blew up to many motors. One turbo (failed tensioner) and two new 2.4S motors (rod/crank) and it was getting expensive and just did not want to go through it again.

Wish they had the fully programmable MSD when I had my 91 C2Turbo. The ignition was a burned in program that was non adjustable except for an octane jumper. It should be such a good fit putting MSD with CIS injection and being able to fully map it. I think it could just use the existing crank sensor to fire it.

I love these cars and have been starting kind of a living document of what I might do next. Mostly I would build a light weight 930 in the form of a 73RS with a track capable suspension but mostly stock appearing for DE's. If I did it today it would have Recaro race seats with plaid inserts and seat heaters so I could run bare headers. ;)

Words don't mean the same thing to different people.
What I mean by locking it down is to disable any vacuum/boost advance/retard function and set the timing at 26 @4K as a base. Then alter the mechanical curve and add back any vac/boost advance/retard function you wish.
Nothing magical.

To improve a 930's ignition we need to come to what the ideal might look like. I contacted Steve Wong of 911Chips.com to see if he could give us any guidance.

I told him our target motor specs were stock 7/1 compression with SC cams, and a decent turbo & intercooler.

I noted that I thought our 930 timing looked as follows:

-15 to -19 on boost
-25 to -29 at cruse.
That idle started near 0, jumped to -10 w loss of vaccum.


He responded as follows:

Brian,

Would love to see someone build a flow bench to re-profile the metering assembly. Could be a major, major contribution.

Got it.

We discussed that possibility/method earlier.

My thought being it is best to start on a dyno with an operator that knows how to get the most out of a motor without going over the top. First to set the "on boost goal" (-26 mightt be leaving power on the table or might be to much for a given motor). Then find the off idle timing goal. Then rebuild the mechanical advance section to fit.

I mightt add:

Disconnecting the vac/boost signal to a Euro and working the mechanical advance should be good as the vac advance is just for cruse.

With a US or 930 dist with the double pot, I would caution that we would need to leave the Boost-Retard side hooked up. We could disconnect the Vac-Retard side or we would not have boost retard and would be running -26 deg on boost which is to much timing on boost to be safe.

On a dual pot, I am thinking I would just leave the Vac-Ret off all together. I believe when Andial sets up a distributor for a customer they say to just hook up the Boost-Retard side and leave the vacuum-retard side off.

In total, I suspect there is solid gain and or piece of mind to be had in the "on boost" section. There should be solid gain to be had in the area off idle on the way to full boost.

I've experimented with modifying the electronic fuel injection and distributors on normally aspirated 2.0 and 3.5 liter BMW engines from the seventies quite a bit.

I took the distributor apart many times on the 3.5, changed advance weight springs and tried enlargeing the slots that control how far the centrifical advance goes with a die grindrer and carbide bur. Felt like I went too far and ended up brazing my enlarged slots back to about the origonal length or dimension and sanding them back to smooth.
I also tee'd into the single vacuum advance line and ran a hose into the car to a little valve I could open while driving to see if I could feel any difference in power while accelerating. I could feel a difference.

In the end I found the stock skinny euro single pot vacuum advance distributor advance curve was pretty good and anything I did to change it was a waste of time and didn't make anything better.
Like most distributors, full mechanical advance was in around 3000rpm and with crap for gas it was best to leave it at that.
I also found that increasing ignition advance a little more than stock in the areas around 1700-3500rpms while the engine was running free with no load made the engine misfire a little. Driving at steady speed on level ground in third gear at speeds around 35mph I would also notice the slight misfire from ignition being advanced too far so that was no good either.

It sounds like some people have gotten a little bit more low speed power by making timing advance more in the 1500-3500rpm range than the stock distributor does with the MSD boost retard box on a 930.
Seems like thats about all you can do to improve the ignition timing and if you buy the stuff to do it new it's going to be around $450 plus your time or labor charges installing and trying to tune it.

Sounds like a really big risk doing that... especially while experimenting with running on the edge of detonation in summer weather unless you're going to rebuild the motor anyway.
There is no way for the average home mechanic to know how far you can go with timing advance without going too far and damaging the motor... then it's too late and you'll wish you didn't mess with it.
Some people don't even know what pinging and detonation sound like and/or their exhaust is so loud you can't hear it anyway.

Having sad that, you could probably take apart the distributor and carefully braze up part of the slots in the plate that control how far the centrifical advance can go to limit it, and then turn the distributor clockwise and tighten the nut to advance the static timing the same amount to compensate so full centrifical advance will be the same as it was.
Idle and low speed timing would then be advanced while full advance would be the same.
If the vacuum and retard pots and vacuum lines are hooked up correctly and working then that could give you a similar final result as buying the MSD boost retard module without spending a bunch of cash on more MSD stuff... and the cold start - high idle - vacuum solenoid in the vacuum retard line could still work too if you want it.

JFairman,

We are very much on the same page in terms of what can be accomplished using the factory distributor.

More advance off idle by shortening of the mechanical advance portion and re-curving should add better response as has been adoped successfuly by some here already.

Keep on boost timing at a proven level.

I might add.

MSD could add its own potential to pre boost operation with or without boost retard or programability.

It might be worth it to verify on boost timing goal on a dyno by starting off at a low timing value and adding it advance to find a safe peak timing on boost to fit the specifics of a given build. We are just shooting in the dark and -26 base timing might even be to much for some builds (1 bar, depending on the turbo, cam, inter-cooler efficiency).

The other way to go being a fully mappable by load (boost/vac) and rpm. This offers more potential as the timing curve could be bent around sensitivity at TQ peak or the less than ideal AFR curve that comes with CIS and better fit to what the motor would take.

This should also allow for more aggressive timing on low load cruse for a significant increase in fuel economy and some increase in throttle response.

Tuners have been finding solid performance increased in the ignition side sense the first motor. We get so in to the fuel and air side and rarely look to the ignition side other that twinpluging with the CIS 930.

A dyno-tune where AFR & timing values are optimized by someone that knows what they are doing is in most cases going to make a significant difference.

Asked Steve more about timing at idle and here was his response.

If your assumption is correct (ie 11 degrees of centrifugal advance and 0 static advance) I dont see how it is possible to set the advance at 29° at 4k as recommended by Porsche: this would be achievable only if vacuum advance was 18° (or just a tad less if you have a bit of static advance) which seems quite a lot! What do you think?

Not sure I understand.

I belive as follows so far:

We have about 10 deg of vac retard or vac advance depending on the pot. Plus about 18 deg from mechanical advance for a range of 28 degs total.

Thus a settinging at -29 at 4000rpm would be about -1 at idle (-19 on boost).

A setting at -26 would be about about +2 at idle (-16 on boost).

All this talk about timining got me to go to my mechanic and "show" me how to properly time my engine... In doing so, we noticed that when we removed the vacuum line from the back of the dizzy, the idle didn't change [he said it should have]. Therefore, the idle isn't "retarding" properly at idle??? Is this correct??

Also, in checking my timing, he came up with:

13-Deg Advanced at Idle
And, -26 Degrees at 4K RPM [with both vacuum lines removed].

How does this sound?

Also, I'm going to have the vacuum pot changed out next week... Or, should I just not worry about it??? It runs really well in the "low bands" right now...

You could put a hand vac on the dist to the low pressure side and with vac it should pull timing back about 10 deg and the rpm should drop. If it dose, it is not the pot. You could also put pressure to the other side and it should retard timing also and drop rpm.

You could put a vacuum gage on the vac line and see if you are getting vacuum. If not, your issue is up stream.

There is a solenoid on that line that stays closed for a short time upon start up when cold to bump rpm. Then it opens after a short time. It would be good if that solenoid fails in a closed position so you would still get boost retard. If that is the case, this might be your issue.

I could be off bit I believe this is correct. Let me know what you discover.

Again, I belive that solenoid is essential for proper retard on boost with the double conection pot. If it dose not close under boost, I suspect there will be no retard.

I have read that some have eliminated it thinking it is a smog part. If I did not have it, I would leave the vac-retard side disconected.

I believe the part most have eliminated or bypassed is the thermoswitch in the picture you posted above. Is this what you mean by the solenoid?

My car never had a solenoid other than the thermoswitch as in the picture above but has the two hose pot/distributor.

Your car dose not have the "electrical on off valve" as indicated in post 81?

It is on the Vac-Ret side (inside) connection to the pot.

Chris seemed to think there might be some magic built into the double connection pot that if it seed equal "boost" signal in each side of the Pots diaphragm it will retard.

We need someone to tee a hand pump to each side of the pot, the car should have a fast idle from being disconnected or fit a timing light. Then when pumped up if will work without the electrical on/off valve, it should retard. If not that valve is essential to on boost operation.

More info from another post on the valve:

Not to worry. The vacuum is ported. It sees no vacuum until the throttle is opened by a few degrees.

SS,

I think the Vac-Retard is on the ported connection just inside the butterfly so it sees vac at idle and retard timing.

Then that goes away when the throttle opens a little. With the the timing jumps about 11 deg.

The front or outer connection is ported outside the butterfly and dose not see vac at idle.

I think this is what you told me in a PM.

Wait, you said the back side. In that case you should see a small timing retard. Did you have vacuum on that hose at idle?

I think that only the later us cars had the solenoids ('86-'89). I think that the earlier cars ('76 to '80) had the cut-off valve. When boost builds up the cut-off valve removes the pressure from the back of the distributor diaphram and dumps it to the air cleaner housing instead. This item is frequently removed.

SS,

What is your opinion of removing the cut-off valve (sounds like a check-valve)?

If there in nothing to stop equal boost pressure from filling both sides of the Pot's diaphragm, it would not be able to retard on boost.

That would not be a good thing.

If somone wants or needs to run without somthing on the Vac-retard side to impead flow, it would be safer to run without the Vac-Retard side from being hooked up at all and just reset the idle at the air bypass valve.

The little vacuum solenoid in the boost retard line only closes during the first minute after a cold start so vacuum retard is blocked and doesn't reach the vacuum retard pot, the timing advances a little because of that, and idle raises about 3-400rpms for that first minute after a cold start.

There is no elctrical or mechanical boost sensor anywhere on the car that closes it during boost and the only other thing in there that could do it is the throttle position switch in the full throttle position and it doesn't affect that vacuum solenoid either... thats real easy to test, just open the throttle all the way with the ignition on, motor hot, and check the wires going to it with a voltmeter.

If you think that vacuum solenoid closes during boost so no pressure reaches the vacuum retard side of the pot, what do you think is sensing boost and sending 12 volts to that solenoid to close it?

The left vacumm solenoid in the picture up the page activates the air pump diverter valves and it is an emission control. That one also has a broken off vacuum line fitting on the top side so it is NFG and is not doing anything.

so safe to disconect the 2 solenoid if we have no cats??
Thanks

I got rid of the one that controls all the air injection crap. I kept the other one so I would have the high idle at startup.

Eric

I think it is safe, if you remove the hose from the back side of the distributor diaphram also.

Here is how I have been told the solenoid works at full throttle: The control unit gets the full throttle position signal from the throttle position switch, AND it gets the speed threshold signal from the speed relay. That is why I think the "Fairman test" does not make it work. To test it, you have to be above a certain RPM (don't know what) AND at full throttle. I never tested it though, so I'm not sure on this one.

That would be cool if you are correct that the vacuum solenoid in the vacuum retard line has dual purposes. Havn't heard or seen any indication that it does though. I guess you could hook up two long wires to it's plug and run them into the car and hook them up to a little 12 volt bulb and see if it lights up under boost while at full throttle.

What speed relay are you referring too?

If you mean the left hand smaller relay under the drivers seat, that one is the rev limiter that shuts down the ignition abruptly at 7200rpm.
I don't think it's a dual purpose relay with 2 sets of points.

The other relay in between it and the K-jetronic ECU is the full throttle enrichment relay which is hooked up to the throttle position switch.
It removes the oxygen sensor signal from the lambda emission control circut and puts it into open loop mode and the frequency valve to a set pulse frequency (70% I think) which richens the fuel mixture a little at full throttle.

Maybe that relay also operates the vacuum solenoid in the vacuum retard line in relation to full throttle position also?
I don't know, yet.

I am glad we are talking about this as I am not 100% on this.

How can the dual connection-pot push against its internal return spring when there is boost filling both sides of the internal diaphragm. With equal pressure on each side of the diaphragm there would be not movement and thus no retard.

Running the car up in the driveway for a test is not going to work. Only on a dyno so there is boost on each side of the throttle butterfly.

To test this we just need a hand pump teed to each side of the pot so it pressurizes each side at the same time. If the distributor plate moves, the timing changes, or idle slows, it is able to retard with equal boost signals.

If not, there has to be a check valve, a solenoid, or something to block the signal on the back side of the can.

Go to post 99. There are two solenoids in the picture. One is probably for blocking the on idle vac-ret signal and the other much be for the air pump.

Also, look at that schematic. I shows the solenoid on the Vac-Retard side of the pot.

Anyone have a hand pump, at tee, and some tubing and willing to test the pot?

What is driving the solenoid during the start up for a higher rpm?

What is used to bump/maintain rpm when the A/C goes on?

If the solenoid is used to block the vac-ret side for boost-retard, all that is needed is a low pressure sensor some where that senses boost in the intake manifold section I would think. I would not think it would depend on the throttle switch.

Anyone have a wire digram and can run down the source of the Distributor?

"What is driving the solenoid during the start up for a higher rpm?"
The K-jetronic ECU under the driver seat.

"What is used to bump/maintain rpm when the A/C goes on?"
Nothing does on a 930.

Having said that I installed a vacuum solenoid with a 10mm inside diameter from a late seventies BMW that bypasses the throttle body and opens when the AC compressor comes on.
It actually raised the idle about 100 rpms when the AC came on so I put a small spray gun ball valve inline with it so I could adjust the AC on idle speed to perfectly match the idle speed with the AC off. Works perfect.

"If the solenoid is used to block the vac-ret side for boost-retard, all that is needed is a low pressure sensor some where that senses boost in the intake manifold section I would think"
If there was "low pressure sensor" on a 930 I would have found it by now and/or someone would have found it and mentioned it by now.
There is no electrical MAP sensor of any kind on a 930.

You may be on to something here.

The only time we need Vacuum-Retard is when at idle. Thus, it could be closed at all other times.

I think there is a switch at the Throttle for idle. Thus, any time off idle, the solenoid valve could be closed.

Better yet, maybe the solenoid is on/ open when energized!

This would be better in the event of failure. With failure in the closed position we still have boost retard and there would be a noticeable increase in idle.

Makes much more sense.

If there is a timer and logic for cold start it cold easily handle not being open above idle.

A note, the ported vac line can only supply vacuum at Idle anyway. Our issue is getting boost there.

We definitely do not want vac retard on cruse.

Vacuum retard while decelerating lowers nitrogen dioxide exhaust emissions and the EPA likes that.
Thats the other reason it exists along with vacuum advance on USA cars with distributors since somewhere during the mid to late seventies.

I tested the 2 vacuum lines today to try and make some sense of it all.
At idle cold the blue, line, to the inner pot originally showed no vacuum then after a few minutes showed 13-15 psi steady at idle. By 4000 rpm it was 0 psi.

The red line, from the temp switch, to the outer pot at idle showed 0 psi at idle and before 4000 rpm it was reading 15-17 psi.
At no time was there any positive pressure on either. I did this while checking timing and my inner pot is blown so was unable to see what effects it actually has on timing. Just my 2 cents..
Very good thread and at a very good time for me

Makes sense and as it should be.

The cold start kills the Vac-retard at first using the solenoid.

The port for the Vac-Advance is a small hole just inside the butterfly. At idle it sees vacuum. When the throttle opens the whole moves to outside the butterfly to where the turbo has built some pressure, even at idle.

This connection is just outside the throttle butterfly at idle and thus would not see vacuum.

I assume you mean you saw vacuum. As the butterfly opens a little this connection moves past the butterfly and the hole then is inside the intake manifold portion. Thus, at 4k rpm steady state you were at no load and were seeing vacuum from the motor as you should.

Under load the intake manifold would fill with boost and you would see positive pressure. You can not get boost in the intake manifold in the driveway.


What do you mean your inner pot is blown?

From all the above it sounds like you are performing correctly.

Quote "What do you mean your inner pot is blown?"
There has to be 2 pots, the outter will hold a vacuum. The innermost vacuum nipple will not hold vacuum. I just figured there were 2 separate pots. I removed dizzy, cleaned and lubed, advance is fine. The inner was just free air with no effect on dizzy. There was evidence of rusty (liquid) running out around vacuum nipple and throughout the whole vacuum line.
I am on hold purchasing a new vacuum assy. and watching this thread for maybe an alternative (MSD).

The double connection pot should only move in one direction. It pushes a rod in toward the dist. The connection on the out side dose so with boost. The connection on the inside dose so with vacuum.

Any movement the other direction should just be the effect of pushing the diaphragm back against its stop.

If the outside holds vacuum that part is intact. If the inside dose not it might mean there is a hole somewhere on that outside of the pot. Your evidence of rust on that side supports this.

Might try putting it in watter and pressurizing it with a hand pump. That air has to go some where. If it comes out the other connection it would be interesting. I would think it would come out from a hole at the nipple connection or around the outside but just guessing.

Interesting.

OK started thinking about this stuff, went out to the garage, and fiddled with the dizzy again. I found of course the outside boost retard port will retard the dizzy under pressure. the inside vac retard under pressure will not make the dizzy move at all. However I tried applying equal amount of pressure to both ports such as full boost, the dizzy would not move. Just as stated by 911ST. Soo, how am I getting boost pressure retard? The vac retard port (inside) must not be seeing boost pressure, or is vented. I think if it were I would have disconnected vacuum lines that popped under pressure. Or does that side of the TB not produce any significant pressure?

Eric

Eric,

You made my week!

Major, major point!

Thank you very much!

This confirms we do not see boost retard without the a proper functioning solenoid.

If one wants to run with out that solenoid, they need to leave the vac-retards side disconnected or configure a check valve of some type so it dose not cancel out the boost-retard function.

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