Wow, that thing had water corroding and killing the insides for a while.
It's hard to tell what is what inside that vacuum pot anymore.

It sucks that Porsche put the 911 distributor and ignition coil right where rain can and will soak it down everytime if given the chance.

Then on top of that add the salt in the incredibly humid here in Florida air near the coast and...

Thats Zane Coker's incredible water to air intercooled amd turbocharged BMW he built.

I've seen it in person and it starts right up cold and runs perfect.
He knows Haltech EFI very well.
The attention to detail and quality of fabrication he has done is absolutely incredible... I hope I get a ride in it someday.

He's rebuilding his 930 engine in his free time right now.

Copterdude,

You are the man!

Looks like condensation leaks down the vac line and sets on the dist can. Maybe inside and out. A little longer tube with a dip at the bottom might keep that from happening.

Will study it further.

Are there limit stops built into the linkage arm?

If so we might be able to increase boost retard range which could come in handy.

The back of the outer pot and inner pot are press fitted back to back and have no stops...appear to be limited by the flex in the diaphram. The notched out area on the control arm is where the springs were in the retard pot.

See 2nd layer diaphram pic.

In the center is where the pots were back to back and fixed. I had to pry the outer diaphram off. It did not take much as rusty as it was.

Thoughts so far.

I am thinking the large diaphragm is best described as the Retard-Diaphragm. Our pot only retards and I believe this is the only working diaphragm.

On a single connection Vac-Advance pot there is a nipple on the outside that feeds the chamber that is sealed. The back side of the diaphragm is open to atmosphere thought the linkage hole.

With a double connection pot we can not just add a nipple to the back as the air would escape out the back with no effect. Thus, with the double connection pot there needed to be a second seal to retain the pressure.

Not sure I see clearly how the nipple on the back of the pot is connected. Is there a hole in the pot around its connection? Is the nipple hard plumbed to the plate we are calling the back diaphragm?

If so this is how the air gets behind the retard diaphragm.

----

It dose not look like the boost side of the retard diaphragm hits the outer shell to limit movement. It looks like the notches in the linkage limits its movement.

I know that Bosch mechanical advance is limited by 2 pins that are restricted in their length of movement by 2 slots in an adjacent steel plate.
You can take a small carbide bur on a die grinder and grind those slots longer to increase the amount of total mechanical advance or partially braze them up with a brass rod and small acetelene/oxygen brazing tip and then regrind them so the slots are shorter to decrease the amount of total mechanical advance.

Just a thought and maybe the vacuum advance has a similar stop that can be modified if you want.

I think altering or shortening the total amount of mechanical advance by shortening those slots and then advancing the distributors static timing the same amount of degrees to make up for the difference is a start.

That would give you more ignition advance at idle and cruise for better low speed response without doing anything to the vacuum lines and cold start vacuum retard solenoid and it doesn't cost hardly anything compared to the MSD retard boxes, it just takes some time disassembling the distributor and experimentation with brazing, grinding, and fine sanding till you get the ignition advance curve where you want it.

The visible outer canister is just a cover. The rear/inner pot nipple goes through a larger hole in the canister and is pressed into a very heavy/thick pot. that pressure or vacuum moves the diaphram back and forth. i reassmebled best I could and the notches do not have anything to lock against. That rear diaphram looks to have had very limited flex. The diaphram was actually a strong sealed cloth material seal around edges with rubber around outer edges giving it flex.
That orfice hole, when acted by press/vac would be pushing and pulling on both diaphrams at same time. Because the orfice is small it, would have just made the press/vac more slow to act. The outer would be immediate and large action.

Jim, I like that idea.

Today, while thinking this whole thing over, I came to the realization that the MSD boost retard does have it's limitations. Without going into huge detail, understand this: the MSD unit retards up to a maximum of 15 degrees, based on how much boost pressure you feed it. With our cars boosting 12 to 14 pounds, the MSD will always achieve the maximum 15 degrees retard...regardless of whether you want it to retard that much or not...because it needs to be set to prevent too much advance at the onset of boost. In my case, with my static timing increased to 8 BTDC, I have the MSD set to shave all those 8 degrees off by the time my boost reaches .3 bar. But...and here's the but....there is a lot of boost left to build, and the MSD will continue to shave off timing until it's reached it's 15 degrees max. So net-net, by the time I'm on full boost, my timing is actually 7 degres less than it would have been without the MSD. In other words, around 9 BTDC at full boost, vs. stock of around 16 to 18.

So, it would appear that gaining the bottom end off-boost response has a price to pay in less advance on full boost. I suspect I'm losing some of the turbo kick because of it.

Thoughts anyone? Unless I misunderstand the MSD's functionality, this is worth exploring. The only way to compensate would be to start with more static advance (like 14 degrees), so that your net timing loss after the MSD retards 15 degrees would be only one degree of additional retard on full boost. And 14 degrees advance is a lot of timing. Make sense? Or am I smoking the wrong stuff in my pipe?

Mark,

If you keep using your MSD in series with the stock retard and you advance your timing 8 deg and want to keep the same amount of stock retard. I would take the 8 deg and if ruining .8 bar take 14.7x .8= 11.76 lbs of boost. You would want 8 deg of retard with 11.76. Thus, 11.76/8 = 1.47 deg per bound of boost.

So, if you set the MSD up so you have 1.5 deg of retard per pound of boost you should come in where you want.

If you want to run 1 bar just do the math. 14.7/8= 1.84 deg of retard per pound.

Having said that, I like the idea of not running it in series but in place of the factory retard.

If you goal on boost is say -18 and you have 15 deg of retard, you could run (18+15=) -33 deg of advance on cruse. At one bar that would be 14.7/15= .98 deg per pound at the most.

If you want you could have it reach full retard earlier by setting it at more than 1 deg of retard per pound.

If you do set it at -33 on cruse, with 18 deg of mechanical advance you would be at 18 deg at idle. If you keep the Vac-Retard functioning you would start another 10 deg lower at idle or at about -8. If you need more mechanical advance do as J says.

Might be a great set up.

I am just not sure how fine of adjustment you can put on the MSD and if you can lock it so it dose not get bumped.

I like the idea of fine tuning the stock set up.

A better set up would be a programmable system set up with RPM by load (vac/boost) and be able to trim the timing depending on the air temp at the exit of the inter-cooler.

This way we could bend the timing curve around any sensitive area like TQ peak or a lean AFR at upper rpm and still have the timing protection of pulling back timing on a hot day for safety.

Could pick up preboost, shorten lag, and increase cruse efficiency from running closer to the ideal.

Would take an investment in tunning.

With the pot do we basically have three pistons.

One on each side of the large retard disk and one smaller one that is the seal that keeps air from escaping out the linkage hole?

The way it looks to me
1. The outer pot is sealed and can move in and out with vacuum/pressure
2. The inner pot is orficed to act on both of the diaphrams. The retard diaphram and then as the pressure/vacuum continues to build it sucks or pushes the outer bellows to assist.

Hey 911

356-930 #27 post
c. P/N 6420 with P/N 8977, aka MSD 6AL with Multi Function Ignition Controller with Boost Control. Improves on a. and b. by providing control of ignition timing by rpm and boost retard onset and rate (up to 25 degrees retard). Boost retard is "additive" to any timing map. In other words, lets one build a detail/custom timing map.
This digitally controllable system can be used to eliminate the distributor’s vacuum/boost advance/retard and mechanical advance.

The 6530 replaces these 2 units and I understood it had up to 25 degrees retard?
If that is correct would it not work better?

It is not clear in my mind how vac/boost gets into the inner champer.

Is the nipple in effect hooked directly to the inner chamber?

If not, would not air pass out the linkage hole?

J,

I had been thinking about this. There is something else we have to keep in mind. Lets say for example we shorten the mechanical-advance function 25%. This will also quicken the time that we achieve full advance by about 25%.

Thus, if we were starting at 1000rpm idle and achieving full advance by 3000rpm. After shortening the weights travel we would see full advance 2500rpm. (25% of 2000rpm range)

This might actually work to our favor.

Assunming we limit advance on the outter end of the weights travel. If we do in on the inner range of travel we migh still get full advance by 3000rpm but we would then proably not see a start of any mechanical advance untell about 1500rpm.



Our main limit seems to be how much timing we can take on boost first. If we could increase this we could bet more advance at idle and on curse.

Then we could shorten up the mechanical-advance to get to our ideal on idle assuming we can still use more advance there.

K

Mark,

Your degrees of retard is adjustable from 0*- 3* per pound of boost. You can take out !/2* pr. pound for a total of 7* at 14lb. of boost if you want. You don't have to use all 15*

Cole

The boost retard function on the SafeGuard has "Start" and "Rate" knobs.

The Start knob lets you set at what psi boost retard will begin. The adjustment range is 0 to 10psi.

The Rate knob sets the amount of retard per psi, and is adjustable from 0 to 2° per psi.

The adjustments can be accurately set using a voltmeter in conjunction with the test points on the front panel. For example, if you don't want boost retard to begin until 7 psi, adjust the Start knob until its test point reads 7v. If you decide you want 1.5° of retard per psi (above the start point), adjust the Rate knob so its test point reads 1.5v. At 14 psi with these settings, you would have (14-7) * 1.5 = 10.5° retard.

The unit also has a FI/NA mode switch that moves the start point by 10" hg, so if the Start knob is set to 0v, "Boost Retard" would start at 10" vacuum. This would be the equivalent of vacuum advance. As you step on the gas and the vacuum drops below 10", the unit would start to retard.


The knock retard function has ten steps of retard. The step size is either 1° or 2°, set by the 10/20 mode switch on the front panel.

The amount of retard per knock event is proportional to knock intensity. The controller can retard up to 14° with a single knock event, applied to the knocking cylinder the next time it fires. Timing on the other cylinders is not affected unless knock is detected in them.

You may be thinking "Oh, it doesn't do anything until it hears knock." You are absolutely correct. However, it responds to knock YOU cannot hear. When you adjust the timing, you really have no idea how close you are to audible knock. How many engines have been lost where the driver said "I never heard it knock."? SafeGuard will prevent that, while optimizing timing in each cylinder.

pic removed see next post

OK, I can't stand it any more. Here is what it looks like in cross-section. It is shown in the full pressure retard position.

There are two diaphrams. The left one is like a donut. The right one is like a dinner plate. The thing in the middle is not a diaphram. It is a damper to keep the rod from shaking back and forth when in the mid-stroke position. The orifice is to make sure that air from behind the right diaphram can escape to the outside. More later.

http://forums.pelicanparts.com/uploa...1254624778.jpg

Speedy
Does the orfice bleed down the center and out back or into pot and out nipple.
The one I tore apart is a bunch of rusty a$$ pieces bent up fro deconstruction.
Cant really tell
Thanks