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Macht Schnell
 
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Hi,
I've always been mystified by the myriad of advance/retard diagrams in the "Cryptic" factory manuals. I really wished they made an absolute manifold pressure trace to help out with figuring out what is going on with the distributer. But here is a quote from the manual:

"The charge air pressure is used for full throttle retard ignition control, to avoid coming into the range of excessive advance ignition at full throttle with the ignition timing which is 5 degrees earlier than the US version."

Page 28-14 in the manual. There is also a graph showing boost retard in the Factory manual and an entry that says you can leave it connected during timing as long as the engine does not go on boost. The graph looks like it retards timing about 5 degrees max.

Additionally, it makes sense that Porsche would retard on boost, and not leave you at full mechanical advance , which is 29 degrees on Euro's and 25 degrees on US plus or minus 4 degrees.

The graphs also show a vacuum retard.

Rarly, do you have the Factory manuals? Perhaps you can elucidate?

The 930 distributer is definitely a complex piece. More complex than one would think for a distributer.
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---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 04-06-2008, 08:37 PM
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Les, you hit the nail on the head.
My explaination was simplistic as this is generally how the distibutors function. If you look in the factory manual (yes I have the manual and the PET and the CD) you will see several ignition curves for different years and type numbers (for different countries). Smog controls further confuse the issue.
My engine is a '78 California, 930/63 if memory serves, and may be the most complex as far as the distributor plumbing is concerned. With that unit I stripped away all of the smog crap and tested the function wich was as described. In the end I chucked that distributor for a single pot Euro that had a more agressive curve. Later on I bought an '86 and played with the mechanical portion of the curve.
356/930, what year and type number is your distributor? Is the smog equipment still intact? I am interested in any difference of function performed by the double pot on that unit vs what I have worked with. We can look up the curve and pot functions/configurations in the factory manuals.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 04-07-2008, 05:21 AM
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356-930, I carefully re-read your post and see what you were doing on the Sun.
I do recall reading in the factory manual about the actual reduction of advance during boost on specific distributor models vs the lack of advance on others. I believe they were later model 930. I also recall that there were switching devices in play that allowed for different events to occur at different engine loads. The manual described a boost retard situation but how that retard came about was not by simple reaction of the pot to the signal. Do you have that information? If not I can look it up in my notes and send it to you. We are not allowed to post pages of the manual here on the board.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 04-07-2008, 07:33 AM
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Quote:
Originally Posted by RarlyL8 View Post
356-930, I carefully re-read your post and see what you were doing on the Sun.
I do recall reading in the factory manual about the actual reduction of advance during boost on specific distributor models vs the lack of advance on others. I believe they were later model 930. I also recall that there were switching devices in play that allowed for different events to occur at different engine loads. The manual described a boost retard situation but how that retard came about was not by simple reaction of the pot to the signal. Do you have that information? If not I can look it up in my notes and send it to you. We are not allowed to post pages of the manual here on the board.
Thanks for the study and info. I appreciate your offer of factory manual data. Thankfully, I have access to the factory manuals.
My donor engine was a '79 3.3 liter and it didn't have any of the switching controls you note were employed by Porsche. That's why I ran the Sun tests, to see how the distributor behaved without vacuum/pressure switching control. I'm satisfied it's ok as is. My only concern is potential damage to the control diaphragms seeing vac/press they might not see if the controls were in place. If the engine starts to mis behave in the future, I'll look first at the distributor.
I run an MSD ignition with an MSD boost retard module and can pull out an additional 15-deg of timing if needed. (It's really advantageous to low end performance to run substantial advance. I presently pull out 3-deg with the MSD - helping to keep the pin in the grenade handle.)
Again, Thanks.
Chris
Old 04-07-2008, 08:50 AM
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Macht Schnell
 
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Quote:
Originally Posted by 356-930 View Post
Thanks for the study and info. I appreciate your offer of factory manual data. Thankfully, I have access to the factory manuals.
My donor engine was a '79 3.3 liter and it didn't have any of the switching controls you note were employed by Porsche. That's why I ran the Sun tests, to see how the distributor behaved without vacuum/pressure switching control. I'm satisfied it's ok as is. My only concern is potential damage to the control diaphragms seeing vac/press they might not see if the controls were in place. If the engine starts to mis behave in the future, I'll look first at the distributor.
I run an MSD ignition with an MSD boost retard module and can pull out an additional 15-deg of timing if needed. (It's really advantageous to low end performance to run substantial advance. I presently pull out 3-deg with the MSD - helping to keep the pin in the grenade handle.)
Again, Thanks.
Chris
What do you call "substantial" advance?
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Old 04-07-2008, 09:55 AM
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Chris, do you happen to know the year/type number on that distributor?
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 04-07-2008, 01:03 PM
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Quote:
Originally Posted by les_garten View Post
What do you call "substantial" advance?
Les:
Donít know what initial timing is now as I didnít check after hooking up vacuum advance. Presently running at 40 deg at 4000 rpm
Without vacuum advance, I ran 35 deg at idle of 1200 rpm (couldnít get idle any lower) so the little car would readily come off the line.
Iíll check timing at idle Wednesday with and without vacuum hooked up, let you know.
Chris
Old 04-07-2008, 04:09 PM
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Quote:
Originally Posted by RarlyL8 View Post
Chris, do you happen to know the year/type number on that distributor?
RarlyL8:
I intended to check that today and report back. Instead, had a Sr. moment.
I'll check Wednesday and hope to find the stamping or tag using a mirror. Pulling the distributor is a major task in this little car but if it's truly important information for you, I'll pull it.
Chris
Old 04-07-2008, 04:15 PM
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Macht Schnell
 
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Quote:
Originally Posted by 356-930 View Post
Les:
Donít know what initial timing is now as I didnít check after hooking up vacuum advance. Presently running at 40 deg at 4000 rpm
Without vacuum advance, I ran 35 deg at idle of 1200 rpm (couldnít get idle any lower) so the little car would readily come off the line.
Iíll check timing at idle Wednesday with and without vacuum hooked up, let you know.
Chris
Hmmm, Interesting, and this is on a 930?
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Old 04-07-2008, 07:10 PM
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Chris,
Don't go to the trouble of pulling it, I was interested in looking up the factory curve for that particular init. The actions you describe make me think it is a later model.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 04-07-2008, 07:49 PM
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Chris, interesting thread, and thanks for your findings.

I agree that 930s respond much better off-boost with more advance. I couldn't live with mine around town when it was retarded 4 degrees over stock - and it felt like it picked up a 1/2 liter big-bore kit with only a few extra degrees. This was done on some specific advice.

I read a little sidebar in the POC GB magazine (think it was in the 930 register section) that stated that the factory timing for the RoW 930S was 25 degrees, but I could never find it again...

I'm really intrigued by the J + S Safeguard, which offers individual cylinder knock retard and, if I'm reading it right, a built-in MAP sensor with adjustable boost retard. Oh, and it's capable of either firing the coil directly or triggering an MSD.
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Old 04-08-2008, 07:24 PM
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Crotchety Old Bastard
 
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Getting more timing in sooner, especially off idle, is an important part of increasing the driveability for the CIS engines. Quite a bit of what folks think is a CIS design flaw is not that at all but simply old school technology and conservative factory tune. Modern exhaust systems, turbos, and ignitions systems coupled with an SC or-like cam can really wake up the old CIS.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 04-09-2008, 01:49 AM
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Interesting thread here guys. I think what confuses me most is the fact that there were so many variations on the dizzys of our 930s over the years. When I see a post describing the pot actually retarding the timing it is confusing, since my 87 us model does not seem to do that. It only retards in the absence of vacuum, it does not respond to positive pressure at all. It seems that the pot in my car is only there for emmisions and cold starting. the retard port is blocked during start-up increasing the idle when it warms the pot sees vacuum. on the advance side the pot sees vacuum increasing timing during warm up, then a solenoid shuts the vacuum off, then with a warm engine the only function of the pot is for ignition retard at idle only, which is gone when you step on the gas. correct me if i'm wrong, i'm still trying to figure this thing out.

Eric
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Old 04-09-2008, 08:50 AM
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RarlyL8:
I/D tag on the distributor is partially mushed. Hereís what I can read:
0 ??? 302 009
Pg ??? 06 >
050

Les Garten:
Checked timing today
Timing at idle (1500rpm),no vac 2 deg
Timing at idle (under 1000), with vac 22 deg
Timing at 4000 rpm, no vac 40 deg
The advice Iíve been given is donít run advance greater than 29 deg but when my timing is that slow, very poor low end/low rpm performance, marginal to poor performance at high rpm.
The distributor I run pulls out 8 deg and my electronic boost controlled retard (MSD) pulls out 3 deg so net advance above 4000 rpm and boost above 6psi is 29 deg.
I was running 40 deg advance without the electronic retard but backed it off when I went to 1-bar boost.

Spuggy:
If the J & S Safeguard device works as represented, one could be employed to safely add a few more degrees of advance and the resultant increase in power.

All:
Please understand I know nothing about these engines other than what Iíve learned on web forums and my own experimentation. Iíve learned that lots of timing obviously has its benefits. Iíve also learned itís risky to an expensive engineís life. Running a lot of timing in a street rod that spends very little time in boost is one thing. Running a lot of timing on a track under boost. . . .
Old 04-09-2008, 11:33 AM
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Les:
I got my idle advance numbers backwards
Idle, no vac 22 deg
Idle with vac 2 deg

Chris
Old 04-09-2008, 11:36 AM
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Great thread guys.....
I am having similar issues with pinging last nite since I changed from a 0.8bar boost spring to a 1.0bar spring.
My car is a 79 930 with the dual port can, the boost retard is open to atmosphere. Vacuum side is connected as normal.
Checked timing and here is what I have which confuses me:
at idle of 1000rpm..... timing = (neg) 7 degrees BTDC VACUUM PORT CONNECTED
at idle of 1000rpm..... timing = (neg) 29 degrees BTDC VACUUM PORT DISCONNECTED
Honestly I was shocked because I thought that the 29 was aweful high at idle because as I rev to 4000rpm (NOT DONE AS YET, SO CANNOT REPORT RESULTS) I expect the mechanical advance to go even higher.
Now the safe limit from other posts I have read under full boost and high revs indicates 26-28 degrees max timing BTDC......I wonder what it will be when I run it up to 4000rpm with vacuum disconnected.
Questions:
1) In short, how much more advance does the mechanical advance add by itself?
2) Are my mechanical advance weights frozen at idle to explain the above results so far?
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---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-10-2008, 02:41 PM
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Quote:
Originally Posted by fredmeister View Post
Great thread guys.....
I am having similar issues with pinging last nite since I changed from a 0.8bar boost spring to a 1.0bar spring.
My car is a 79 930 with the dual port can, the boost retard is open to atmosphere. Vacuum side is connected as normal.
Checked timing and here is what I have which confuses me:
at idle of 1000rpm..... timing = (neg) 7 degrees BTDC VACUUM PORT CONNECTED
at idle of 1000rpm..... timing = (neg) 29 degrees BTDC VACUUM PORT DISCONNECTED
Honestly I was shocked because I thought that the 29 was aweful high at idle because as I rev to 4000rpm (NOT DONE AS YET, SO CANNOT REPORT RESULTS) I expect the mechanical advance to go even higher.
Now the safe limit from other posts I have read under full boost and high revs indicates 26-28 degrees max timing BTDC......I wonder what it will be when I run it up to 4000rpm with vacuum disconnected.
Questions:
1) In short, how much more advance does the mechanical advance add by itself?
2) Are my mechanical advance weights frozen at idle to explain the above results so far?
The results you posted are the result of vacuum and absence of vacuum. The mechanical advance, whether working or frozen, has no effect at low rpm. Itís a centrifugal mechanism and dependant on rotational speed and speed change to act on timing. Donít know where it begins to move but not likely under 2,500 rpm.
Remember, the term vacuum advance is misleading. When a vacuum is pulled on the vacuum port of the distributor, it retards the spark. As vacuum decreases with rpm increase and/or engine load, timing advanced due to the loss of vacuum.
Based on your posted data, you are 7 deg advanced at idle with vacuum. Loss of vacuum moved timing to 27 deg or added 20 deg of timing which is as it should be.
Mechanical advance may vary from distributor to distributor but expect 18 deg.
Timing with full centrifugal advance in will then be 45 deg. If you hook up the boost retard (uses same line as the vacuum line) 8 deg of timing will be pulled out above 5-psi and net timing will be 37 degrees.
Based on the factory setting (29 degrees is marked on the crank pulley) 37 is a bit much.
I find it reliable on my í79 930 engine to disconnect the vacuum to the distributor, plug the vacuum line, run the engine up to 3500-4000 and advance the timing until the engine starts to stumble, back it off till itís running smooth again and lock it down. The point the timing makes the engine stumble is a nominal maximum timing level. With the vacuum hooked up again, suspect you will be close to 0 degrees.
If youíre not running boost retard, Iíd be nervous with timing in excess of 29 degrees at 4000, especially under boost with a potential of getting to 1-bar.
You should also be nervous if you donít have a handle on the engineís AFR under boost.
Old 04-10-2008, 06:58 PM
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Quote:
Originally Posted by fredmeister View Post
Great thread guys.....
I am having similar issues with pinging last nite since I changed from a 0.8bar boost spring to a 1.0bar spring.
My car is a 79 930 with the dual port can, the boost retard is open to atmosphere. Vacuum side is connected as normal.
Checked timing and here is what I have which confuses me:
at idle of 1000rpm..... timing = (neg) 7 degrees BTDC VACUUM PORT CONNECTED
at idle of 1000rpm..... timing = (neg) 29 degrees BTDC VACUUM PORT DISCONNECTED
Honestly I was shocked because I thought that the 29 was aweful high at idle because as I rev to 4000rpm (NOT DONE AS YET, SO CANNOT REPORT RESULTS) I expect the mechanical advance to go even higher.
Now the safe limit from other posts I have read under full boost and high revs indicates 26-28 degrees max timing BTDC......I wonder what it will be when I run it up to 4000rpm with vacuum disconnected.
Questions:
1) In short, how much more advance does the mechanical advance add by itself?
2) Are my mechanical advance weights frozen at idle to explain the above results so far?
Meister,
When I told Brian Leask that I was ready to go to a 1 bar spring, he suggested purchasing a modified fuel head from IA. He said that I'd need the 20% extra fuel otherwise full boost enrichment would prove lean. I have the PLX afr gauge, thus I can tell you that at 1 bar WOT, I ain't lean. Along with the fuel head, I had to buy the rpm activated solenoid from Brian. Of course, the adjustable WUR is part of the equation too. I'm sure lots of people run 1 bar without the extra fuel, but I wonder what kind of readings they are getting, if any at all. I assume that with a 1 bar spring, an afr gauge is a must.
Old 04-10-2008, 07:19 PM
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Quote:
Originally Posted by 356-930 View Post

Les Garten:
Checked timing today
Timing at idle (1500rpm),no vac 2 deg
Timing at idle (under 1000), with vac 22 deg
Timing at 4000 rpm, no vac 40 deg .
Hi,
Thanx for that!!

Les
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Old 04-10-2008, 07:44 PM
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Quote:
Originally Posted by 356-930 View Post
The results you posted are the result of vacuum and absence of vacuum. The mechanical advance, whether working or frozen, has no effect at low rpm. Itís a centrifugal mechanism and dependant on rotational speed and speed change to act on timing. Donít know where it begins to move but not likely under 2,500 rpm.
Remember, the term vacuum advance is misleading. When a vacuum is pulled on the vacuum port of the distributor, it retards the spark. As vacuum decreases with rpm increase and/or engine load, timing advanced due to the loss of vacuum.
Based on your posted data, you are 7 deg advanced at idle with vacuum. Loss of vacuum moved timing to 27 deg or added 20 deg of timing which is as it should be.
Mechanical advance may vary from distributor to distributor but expect 18 deg.
Timing with full centrifugal advance in will then be 45 deg. If you hook up the boost retard (uses same line as the vacuum line) 8 deg of timing will be pulled out above 5-psi and net timing will be 37 degrees.
Based on the factory setting (29 degrees is marked on the crank pulley) 37 is a bit much.
I find it reliable on my í79 930 engine to disconnect the vacuum to the distributor, plug the vacuum line, run the engine up to 3500-4000 and advance the timing until the engine starts to stumble, back it off till itís running smooth again and lock it down. The point the timing makes the engine stumble is a nominal maximum timing level. With the vacuum hooked up again, suspect you will be close to 0 degrees.
If youíre not running boost retard, Iíd be nervous with timing in excess of 29 degrees at 4000, especially under boost with a potential of getting to 1-bar.
You should also be nervous if you donít have a handle on the engineís AFR under boost.
This is exactly what I stated in my post, except I see 22 degrees of advance without vacuum connected because it runs right up to the 29 degree timing mark, I guess this is still within tolerance of 20 degrees which you said was normal.
But what bothers me is the fact that with 18 degrees allowable in the mechanical advance, this puts me at 47 degrees BTDC at 4000rpm with my current set up.
Now if I hook up the boost retard line and get back 8 degrees that leaves 39 degrees total under boost conditions. This still is about 12 degrees too far if you target 27 degrees BTDC at 0.8-1.0 bar boost which from previous posts on the forum I see as safe limit. Is 27 degrees too conservative or can I run more safely? What is a real safe timing limit above 27 degrees I hope.
In order to get here I need to run 5 degree ATDC timing at idle.....and from my experience the driveability of the car at low rpm is absolutely horrible at this setting. I have even run around 0-1 degree BTDC before and this is the reason I am now at 7 degrees BTDC.......
I cannot see how the factory set the car to run at 5 degrees ATDC and got the car to move out of its own way at low speeds.
Last season when I was running the 0.8 bar spring at these same timing settings it ran well and I never heard pinging. I just wonder if it was still happening just not audible enuff for me to pick up on it, or if something has changed in my distributor over the past few months.
Need to try teeing the vacuum line into the boost retard fitting on the dizzy can and at least getting that amount of retard back....thanks for the tips.
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---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-11-2008, 08:08 AM
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