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.