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Ultimate 930 Distributor, advance, retard, timing, Turbo lag, MSD, mod, thread.

How can we improve a 930's ignition?

I suspect there is a solid improvement to be made in off idle response, spool time, and fuel economy.

To see the potential of a more ideal timing, just pull the vacuum line off the inside connection to the vacuum-boost-retard-can on the distributor at idle. This will advance timing about 9 deg. Idle will increase about 300 RPM because the ignition will be closer at a more ideal setting. With this it will make more power with the same amount of air and fuel. Timing is ideal if combustion pressure reaches its max at about 12-14 After Top Dead Center on most motors.

I have reviewed many of the threads on timing and it looks like there seems to be some general misunderstanding on how our system works and a fair amount of miss-information. Further, most do not seem to know what a more ideal timing curve might look like. Together, lets fix this.

There also seems to be very few solid suggestions on how to make improvements in if there are they have gottin lost among all the clutter. Some even believe that some of the 930 tuners have figured out how to make improvements but are not talking.

When the 930 was built Porsche seems to have made many design accommodations in the name of emissions. They shaved most the cooling fins off the cylinders to get the motor to run hotter, they put a cat on it, they added an air pump, they put small intake ports and funny tops on the pistons to get a better air/fuel mixing and who knows what else.

They also seem to have made compromises with the ignition by adding a Vacuum-Retard function whose prime function is reported to increase heat in the motor for emissions. This appears to be at the expense of low rpm throttle response.

Of course the best way to achieve ideal timing would be to change to a fully programmable system and abandon the weights & springs with vac/boost-retard can. Porsche did this with the C2 turbo.

I am thinking one possibility for a best practices set up would be based on the newest fully programmable MSD with a locked distributor. However, I suspect significant improvement can be made with the stock set up by re-curving the distributor and shortening the mechanical advance to increase the advance off idle.
Old 09-23-2009, 10:41 AM
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So what is our timing like and what would a more ideal look like?

For a stock US 930 I believe our timing looks approximately like this.

+1 (1 deg ATDC) at idle (quickly jumping to apx -8 with acceleration),
-26 (26 deg BTDC) at cruse above 3000rpm,
-16 to -17 on boost.

This comes from a combination of the following:

-Vacuum-Retard of about 9 deg. When this goes away with acceleration and effectively advances timing. There is no vac-advance on 3.3 Turbos. In general I belive vac-advance is to increase economy and vac-retard it to benefit emissions.
-Mechanical Advance of about 18 deg that is full in by about 3000rpm.
-Boost-Retard of about 9 deg. that is full in by about 5 psi.


What would a more ideal timing look like”?

I would love to see more input on this but one EFI turbo ignition timing table reviewed leads me to think it might look more like the following:

-15 (or more) at idle (w aggressive advance by 2500rpm)
-35 on cruse (seen reference up to -42 w little load)
-16 on boost

Our net on-boost timing seems good. We come up short with on cruse timing. However, cruse timing dose not seem hurt our performance to a significant deg. It dose however cost us, by one report, about 5% in fuel economy. Our best and most usable opportunity seems to be to improve idle and pre-boost acceleration. More low-end could also mean earlier boost onset. Further, our boost-retard seems to be all in with about 5 lbs of boost. Bringing this in, in a more progressive manner might reduce spool time.

Thus, we can do better!

Last edited by 911st; 09-23-2009 at 11:33 AM..
Old 09-23-2009, 10:41 AM
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First however, it might be worth testing to see if it is worth the effort. I am thinking we should test the low-end opportunity from more advance and the on boost opportunity to find our truly what our timing goals should be.

Testing low end timing advance.

This can be done as simply as resetting idle timing advance from the stock +1 (1 deg ATDC) with a timing light and going out and doing some acceleration runs up to 2500rpm. Do not go into boost much as you may not have enough boost retard protection. I suspect we could bump timing to about -6 to 9 deg at idle and feel the difference.

I would like to suggest that we also test eliminating the Vac-Retard function that comes from the fitting on the can at the distributor and closest to / facing it. Some of my reading indicated that vac-ret was added to cars to make them run hotter at idle for emmissions. When this is done idle will increase about 300rpm because timing is set to a more ideal level. If we try this we would just re-adjust the Air Bypass screw to reset idle. Timing will jump to about -8 deg at idle from this alone. Try adjusting for more advance and idle should increase further. Again if the idle increases is an indication that timing is at a more ideal point for the amount of load and AFR at that time. However, under load we can not take as much advance as when not under load. If we go to far the car will balk and tell us. Most likely we will get to the end of the adjustment range available at the distributor before we reach the best advance for acceleration. I suspect about -15 is going to be a good place to be.

Of course a better test would be to find a dyno and a good tuner to supervise and do runs from 1000rpm to 2500 or a load type dyno so load can be set at say 1500rpm and then advance timing from stock a little at a time and then backed off a little once the most power is found.


Testing Full Power timing under Boost Retard:

This is more involved and best requires a dyno and the supervision of a good tuner. I am thinking we would start by setting timing per factory procedure but at a lower setting to something like -22. I suspect we should use tune for max power at “Torque Peak” instead of HP Peak as or point of reference. My reasoning is at TQ peak we are most sensitive to detonation (running rich at TQ peak could be an advantage). I would verify AFR’s to be no leaner than 11.5 (or what ever your tolerance for risk and beliefs dictate).

From there after, try advancing timing some and retest until TQ is maxed and back off a little for safety. This should give us an indication of our ideal timing given our build and the type of fuel we are running.

We will probably not know our actual timing goal under load unless we sit on the timing light when on the dyno. We will have to back into it.

Until then I suspect we want to be at about -15 to -18 at full boost.
Old 09-23-2009, 10:42 AM
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How do we improve the existing 930’s ignition.

I am thinking the following methods might be worth considering.



MSD, fully programmable:

MSD-6AL-2 Ignition Control - 6421

I suspect can we not only get more ideal timing using a programmable ignition system, MSD offers a unique advantage in that at low rpm its higher intensity and ability to generate multiple sparks will be more effective at burning a lean air-fuel mix that is typical with a boost-enrichment WUR that dose not have acceleration enrichment capability. This is one of the prim advantages of twin-plugging a CIS Turbo.

Thus, it would be a double win!

Because of emissions goals and limitations of using a “weights & springs” mechanical advance with a vacuum canister, we should be able to make improvements in the following areas.

Of idle: We are at about +1 deg at idle jumping to about -8 off idle when we blip the throttle. I suspect we should be closer to -15 at idle and to about -22 by 1500rpm. This should increase throttle response off idle, get us to boost onset faster, and even lower the boost onset point. It will also make for a cooler running motor at idle.

Cruse: If we time our cars to run on US fuel with the stock system we are going to be at about -25 or -26 at curse. Our low compression motors when under the low demand of cruse I suspect can benefit from being at about -36 and read of one built turbo running at -42 on the freeway. This should help efficiency /fuel economy significantly as much or more that 5%. Fortunately, running less than ideal advance at cruse dose not effect the ability to make power.

Boost-Retard: The stock system goes to full retard at about 5 PSI. Thus, it is kind of an all or nothing. This might be less than ideal. If so pulling back boost in a more progressive manner might add some power to the spool part of our operating range. Spool being that point between boost onset and full boost. Further, with the stock 930, Boost-Retard is a fixed position. If one runs .8 bar and wants to jack boost to 1 bar from time to time, one would have to compromise on the side of safety and run less advance at the lower boost level. With a programmable system we can better fit the boost timing to the actual boost level. Additionally, as a motor is more sensitive to detonation near Torque-Peak, a programmable system should allow us to bend the advance curve around TQ peak and thus make more HP later in the rpm range with more ideal advance.

With this system I believe we lock out the existing mechanical advance and set timing to about -16 and eliminate the retard-can. We then use the stock trigger signal and plumb in GM MAP to the intake manifold for load.

Thus, combining fully programmable MSD with CIS could be a powerful combination and improvement.
Old 09-23-2009, 10:43 AM
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Modifying the stock system:

Because of the design of the stock system it is not a good idea to just set the timing for more static advance. This is because the on boost timing will move with it. Thus, on cruse advance is going to mostly have to be lived with at the expense of MPG. Again, this dose not have any solid impact on performance.

On Boost: Setting the stock US dist at -26 deg yealds about -16 to -18 deg of advance on boost. I suspect we really need to be near the lower end of this for safety. Bruce Anderson in his book on modifying Porsches suggests setting timing at -25 if running .9 bar boost on a modified 930. We do not want to advance this any furter.

Off idle: It looks like -15 with very quick advancement offers better throttle response. To get this the best way will probably be to shorten the mechanical advance feature. Further, we see full advance by -3000. Some readings seemed to indicate that we might benefit from seeing full advance by 2500rpm. How do we modify for this. One is to “re-curve” the distributor by putting softer springs in it so the weights advanced faster. The other is to shorten the mechanical advance. This can be done by limiting how far the weights are allowed to extend.

How much we limit this is open for debate. I am leaning toward killing the Vac-Ret function totally. This would advance the timing to about -8. If my goal is -15 at idle that means we need to take about 7 deg out of the mechanical advance. 7 deg of 18 is about 40% of total advance. Thus, we would need to reduce the weights ability to advance about 40%. This will effect when we get total advance and it might make total come about 25% faster so this might be all we have to do.

If however one wants to keep the Vac-Retard function to maintain the increase in rpm that is available during the cold start function (and maybe A/C tuning on but not sure), we might target something like -10 at idle with every thing hooked up. That would mean taking about reducing mechanical advance about 11 of the total 18 available. This is about a 55% reduction in weight travel.

This, we should be able to increase our off throttle response by shortening the mechanical advance part of the total advance available to us.

Note: I suspect the small solenoid that is hooked up to the low pressure side of the distributor (Vac-Ret) has an important function in achieving boost-retard. If this solenoid id not function, boost will enter both sides of diaphragm on the distributor and in effect equalizing pressure on both aides keeping it from retarding. One resource indicated that with his test, applying boost to both sides of the retard-can still retarded boost, however I would not want to count on that.

Last edited by 911st; 09-23-2009 at 11:41 AM..
Old 09-23-2009, 10:44 AM
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MSD with Boost-Retard in series w stock.

This is being done by a couple here. With this timing can be advanced from -25 to about -36 using the factory timing method. Thus, gaining fuel economy at cruse. It also advances timing off idle from +1 to about -9 for improvement off idle. The boost-retard available from MSD then is used to pull timing back the 11 deg that static timing was advanced. The added benefit being the higher output at low rpms where we can use it. Further, it was pointed out to me that another advantage to this set up it is easier to back things out of one has issue meeting smog cert’s if needed by disabling the MSD retard and retiming the car. (Thank you Chris Toy “930-356” for suffering through my questions and helping be better understand a 930’s ignition.)
Old 09-23-2009, 10:44 AM
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MSD w Boost-Retard substituted.
This might have some potential and involves disabling the Vac/Boost-retard canister on the distributor. It can gain many of the advantages we seek plus having timing on boost come in, in a more progressive manner. (I suspect if I was building a 930 today this might be what I actually do a version of this but play with the mechanical advance. )

There is a limitation with this unit in that it can only retard timing a max of 15 deg. Thus, if we want total timing on boost to be at -16 we can set total timing at 4000rpm at -31. This is better than -26 but short of cruse ideal so we should see some improvement. If total timing is at -31, 18 deg of that would be from mechanical-advance. Thus, timing at idle would then be -13 which should be a solid improvement but probably less than the motor would take. This approach might benefit from a softer spring in the distributor that would bring in total advance in faster. Optionally one might hook up the Vac-Ret hose (closest to the motor) if desired for a bump in rpm during cold start and bring idle timing to about -5 deg.
Old 09-23-2009, 10:45 AM
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Disclaimer:

I am not an expert, just someone that loves figure out how Porsche’s work. First is was MFI where I eliminated the thermostat, adding an external AFR adjustment knob to the injection pump, remote cold start priming, and grinding on my own space cam for my 2.8 twin plug build. Next it was CIS when about 7 years ago I set up my own WUR add on that was programmable for all loads and rpm levels so I achieved near ideal AFR’s everywhere, more fuel up top, and increased throttle response. Way before the D-WUR popped up. My thoughts also resulted in the first higher flow fuel head that went to Brent 930 that then became the HF head. I also first suggested the use of the RPM boost circuit clamp using an MSD switch that was just one way to try to tame the increased fuel that came with the modified fuel head and a desire to access increase fuel needed up top by lowering control pressure (a reverse Andial-Fueler approach).

I make a lot of mistakes along the way to learning and might have made some here.

However I hope other’s will offer positive correction where needed and new ideas so we can all benefit.

Old 09-23-2009, 10:46 AM
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Great start on what may prove to be another great thread!

I know of three of us (myself, Chris, and Cole) that I believe are still using the MSD boost retard module to gain controlable advance and to shave it off progressively as boost builds. I think Chris is running with the most static advance (and until I re-index my distributor, I'm stuck at 8 degrees max). Besides the improved lower end power and response, I'm getting very close to 20 mpg when just sanely crusing down the highway.
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Old 09-23-2009, 11:31 AM
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I like what you guys have done. Better timing and a better quality spark with the MSD. You probably have not left much on the table to be improved.

I do not want to slight the stock components as if AFR's are well managed the stock components are very solid.
Old 09-23-2009, 11:50 AM
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great thread, and just in time for me to work on the timing table for my EFI/ignition control project. It has been explained to me like this: An engine at WOT is at it's highest efficiency, any throttle less than 100% is less efficient and therefore needs more timing advance to compensate. In my experience with user programable efi i always targeted 25-30 advance at idle then moved to 35-38* as the engine approached 2500rpm and keep it there till the onset of boost. So i tend to agree with everything you've mentioned so far, except i will not be keeping the dizzy. crank trigger/coil pack and full user control is the way i'm going. I'll be able to dictate how much timing the engine will see in every rpm/load scenerio possible.... my biggest issue right now is WHAT those numbers should be.... i'm all ears
Old 09-23-2009, 07:33 PM
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Individual cylinder knock retard is also quite useful
Old 09-23-2009, 07:34 PM
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Well here goes a "for what it's worth"

First, thanks to Keith we are looking at a topic that is rarely discussed and very misunderstood by most of us. I have been looking at timing for some time now as I think it happens to be a largely overlooked performance enhancement that is nearly free compared to some of the mods we do.
As we start here remember that the word death is actually spelled "detonation" and you need to know how to avoid it because it will destroy an engine in a millisecond. So before you even think about screwing with timing make sure you have considered the following preventative measures. Never run pump gas go find the highest fuel you can get and use it religiously, install a larger intercooler, definetly have a system to monitor AFR's and know what your afr's are always, make sure you have a good free-flow exhaust or header system, consider running one range cooler plugs, and don't screw with the timing without knowing what your doing.

I am aiming this at all us poor bastards that can't afford to destroy a motor
and go buy another tomorrow and run the standard bolt on type mods. Our cars call for around 0 - 4 degrees at idle and 26 - 29 degrees at 4000 rpm. A couple little tid bits: you can actually experience detonation in the 800 -2500 rpm range if you advance initial timing too far. At higher RPM's we don't need excessive timing because our engines are relatively low compression and excessive timing increases the chance of detonation, cools exhaust temps, and creates power loss. Excessive retarded timing at higher RPM's will create excessive heat in the heads and cylinders and loss of power.

From what I have gleaned from a lot of reading is it's good to add about 6 - 12 degrees of initial timing as this will improve low end performance, but once you reach about 2 psi of boost you need to start retarding timing and end up at the 24-26 degree at 4000 rpm. There are several ways to do this. I have a MSD6AL and a MSD Boost Retard in the "Old Sled" which makes it pretty easy. There are also ways to replumb the distributor pot to retard timing when intake pressure becomes positive at boost. Also the distributor can be recurved by changing springs and weights.

Hopfully someone smarter than me will tell me I'm full of s--- and we can get this thread moving.

Untill then this is my story and I'm sticking to it.


Cole
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Last edited by cole930; 09-23-2009 at 09:30 PM..
Old 09-23-2009, 09:17 PM
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Old 09-23-2009, 09:29 PM
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Yes, an A/F ratio gauge is good, but it can't detect knock or do anything about it. Running rich doesn't guarantee you are safe.

If you are worried about detonation, get a system that can respond to inaudible knock and keep it inaudible.

Here is a link to a short clip that shows an individual cylinder knock controller on an engine tuned for 91 octane, but running a 50/50 mix of 89 and 91. The system is responding to inaudible knock:

bgstew6's knock controller demo

Your engines are rare and expensive. The knock controller is a small price to pay to protect it, and it won't slow you down, since it retards only the knocking cylinders.
Old 09-23-2009, 11:55 PM
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Old 09-24-2009, 12:08 AM
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Cole,

Thx! I am sure I still have alot to learn and am glad to get your imput.

Everyone wants to run 12/1 AFR w big boost and they are not looking at the ignition side.

I am concerned that many of us are running to much advance on boost and do not even know it.

I suspect that the original stock setting at -26 US at 4000rpm may not be enough for a built car. Again, Bruce Anderson notes setting it to -25 for a car that runs .9 bar or has limmited runs to 1 bar. That was written years ago and I think before we started getting the gas with alchol in it. Also, one ignition sheet I was given showed that timming on boost was pulled back with more boost retared of about 1.7 through 1 deg more when going from .8 to 1 bar boost. Thus, we might want to look at setting timming at about -24 for a car with a health unmodifed igntion if running more boost.

We need to build safety in to the tuning of a 930. It dose not have the ability to adjust timming and fueling with temp or altitude like the more modern cars.

Timming on boost is directy tied to full timming is set at on these cars and is retarded about 8-10 deg from that setting. Anyone that sets there timming at -29 probably better be running race fuel because they could be at -20 on boost and need to be as low as -15 or so.

Yes, run the best fuel possable but set up your car to work with what ever you usally run.

Detonation is not directly tied to timming. Pre-ignition is. Detonation is when there is ignition from heat or compression before the spark.

Anyway. When I was big on understanding CIS I concluded that one of the reasions for the high rate of failures with 930's was because of the potental for uneven fuel flow per cylinder (others say uneven air flows).

As such I am a big beliver is having the injectors cleaned and matched and the head ballanced so we are not in a suituation where we think we have a healthy AFR of say 11.3/1 on boost but have one cylinder at 14/1 with the others at 11/1.

Now that I am looking at the 930 ignition side it looks to be succeptable to failure. If the vac hoses are not in good shape or the diphram in the retard-can is leaking we will not get retard and will be pulling -25 deg when we should be at about -15. This system dose not fail toward retard. If fails and we get no retard but do not know that is what happened.

Also, there is a little solonid on the vac-ret side of the can the seems to be essential to getting boost retard. That solonoid really needs to close on boost. If it dose not, both sides of the can recive a boost signile that should cancel each other out. I suspect if that happens, we will not get our boost retard.

One member I talked with thinks the dist has some magic in it that if the dist dose get an equal boost signle to both sides of the retard-can it will still retard against its spring. It would be good to have someone put a hand pump tee'd to both sides and add pressure to see if this is true. I am very suspect.

If I were doing a 930 I would 'look at' removing the Vacuum-Retard side at the can so I would not have to wate for the vac to go away to get my advance and to protect me a little bit more from failure.

Thus, we are probably running to much timming to begn with for a motor that is running higher boost, we probably have less than ballanced AFR's at each cylinder, and have a higher than average suseptibility to ignition failure that would limit our boost-retard without us knowing it.

Last edited by 911st; 09-24-2009 at 06:27 AM..
Old 09-24-2009, 06:22 AM
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Old 09-24-2009, 07:27 AM
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MSD!

Mark, Chris or anyone that has done an MSD conversion, can you confirm what needs to be done?

Tach drive?

Rotor, eliminate resistor?

Rev-limiter, do we need a "pill" at the MSD box to reestablish the rev limit?


MSD in concept is a great fit with a 930's lower compression ratio pre-boost than almost any other turbo cars and with it's CIS that tends to have a lean surge off idle. These two factors make for potentally a difficult mix to fire. Outside of twin-plugging it seems a very good way to address this. Even if it is not used for any other purpose.
Old 09-24-2009, 07:46 AM
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Keith,

I have an 80 ROW 930 and therefore have a single pot distributor and the factory timing spec is 29 degrees at 4000 RPM. Total distributor retard is 4 degrees. I used to re curve distributors on small block Chevy by changing springs and weights. Jerry Woods at Smart Racing will still rebuild and re curve a distributor if you send it to them. So there are still resources out there.

I personally think twin plug and programmable digital timing control is the right choice if you are running a serious track car, just like EFI is the way to go for fuel. But none of this is practical for the average smuck like me running on the street. Hell that 16 grand it takes to twin plug and EFI would actually pay for 1 of the 18 chemo treatments I'm still paying for, so The Old One goes to Evil Bay and buys MSD parts.

I have a MSD 6AL 6420 $64.00 and shipping used, a MSD Boost Timing Master 8762 $34.00 and shipping used, a MSD 8920 Tach Adapter $40.00 and shipping new, MSD 8207 Blaster coil $28.00 and shipping, Porsche non resistor rotor from our host $15.00 and a new set of Magnecor 6594 Plug wires on line for $140.00 and shipping. I have a total of $321.00 in parts and sold my Bosch CDI and Coil on the board for $350.00. Probably not the best system available but it really works great for a street car and I am very pleased with it. I made up a harness that allows me to plug directly into the original engine harness connector. Pretty sweet set -up. I run the MSD with a 6000 RPM pill.

Cole
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Last edited by cole930; 09-24-2009 at 10:17 AM..
Old 09-24-2009, 10:08 AM
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