Bosch CDI Compatible with MSD Coil?

[Mr.P 911T 1970]

Aloha,

Merry Christmas. Appreciate you all who take the time to reply to the forums - very grateful for the community.

Now on to the real business - the issue.

CURRENT State: Rebuilt my 2.2T - new pistons (S), new cams (E), new PMOs, rebuilt distributor, plugs, CDI, PMO fuel regulator, etc.

PROBLEM: Runs great, very rich and hard to get the initial ignition on the start, takes a couple of tries. Using non-ethanol gasoline only 89 - 93, hard to get higher octane on island. I checked all six plugs with valve adjustment and the plugs were blacked up.

IMMEDIATE SOLUTION: So, we drop the fuel jets from 120 to 115 size and swapped the plugs from NGK 7 to 5s. The engine and throttle are a little bit more "snapper", good response. Yet, I'm still rich and difficult to get that good ignition response.

Feels like I need more (hotter longer) spark...

It was suggested that I switch my ignition coil from the Bosch to MSD. Is the original Bosch CDI compatible with the MSD coil? Blaster Series? High Vibration? Which one?

What about re-gapping the NGK5s to something larger after adding the MSD Coil? How about new spark plug wires from 7 to 8.5mm?

I want to incrementally walk myself into the ideal solution without changing too many variables at once or like installing whole MSD box system

Mahalo!

[Bob Ashlock]

In a normal situation, a properly working Bosch CDI unit and its original German made Black CDI low inductance transformer (coil) is more than adequate to fire your engine right up and have it run strong. When properly tuned, these engines start right up with no drama, so I'd be looking elsewhere AFTER determining the stock CDI box and coil are actually good. What you describe points more to fuel mixture/tuning issues.

Substituting the original Bosch CDI coil with an MSD blaster is routinely done. In my opinion, it is not the best solution because that MSD coil has considerably higher inductance that results in a somewhat weaker appearing spark. And slapping a multiple-spark MSD box on may make it start easier and run better, but I submit that would be masking the real tuning problem.

[Schulisco]

Definitely check the mixture with a lambda tool, both cold and warm. Guessing it's still too rich. The CDI generates such a strong ignition spark to ignite a rich mixture as well. (This is one of benefits why Porsche introduced the CDI). How is the idle CO adjusted? (factory setting was 3,5-4% or carburetted 911T).
Does your distributor work properly? Check out if the advance works correct as given by from factory, especially for the lower rpms before start (almost 0° adv on start, up to 35-40° on 6000rpms on carburetted engines, depending on yours and the mixture (the richer, the more advance and vice versa) and the fuel; 40° is pretty high! Be aware of damage!
Are you sure that the PMO's won't run empty while sitting? It's a common problem on some carburetted Porsche or beetle engines after sitting a (longer) while that the carbs run empty and the fuel pump requires some time to refill the carbs while cranking. Does the engine starts the second time better? If so you can add a second fuel pump parallel to the normal one operated by a push button on the dash to refill the carbs quicker.

Originally Posted by Mr.P 911T 1970

Feels like I need more (hotter longer) spark...

It was suggested that I switch my ignition coil from the Bosch to MSD. Is the original Bosch CDI compatible with the MSD coil? Blaster Series? High Vibration? Which one?

Have a look on this page: https://www.911-hkz.de/Zuendspulen.htm (automatically translated by Google translator) Check out the full text, below there's more about the MSDs.

Thomas

[Mr.P 911T 1970]

Thanks Bob and Thomas, I will do both.

Today, we replaced the new Bosch transformer with an earlier (black) one from a '78 SC and it certainly made a significant difference - fired right up and I got my "snappiness". My idle went from 850-900 rpms to 1050-1100.

We discovered that the newer one installed was incorrect, it was intended for '65-68 model years...confused on how that got into our BOM for this project but we had been collecting parts over a 2 year span.

I cleaned out the tail pipe - removed all the black soot and snapped some before pictures. We'll finish off this tank and give it a break for the holidays and will reengage in the new year.

Now, we are back to 0...but feeling better about dialing-in the fuel/air ratios, advancing, and a better replacement transformer (I hope one is out there somewhere).

I'll keep this post going, hopefully, someone else will get some benefit out of it.

[Mr.P 911T 1970]

For those who haven't read the article that Thomas provided, it's a must read.

I tried to read it with 3 hours of sleep and looked Greek to me...but now that I have time, whoa...really gives insight on the transformer behavior characteristics between the historical Bosch "black" and the newer replacements. Definitely good variables to consider in making decisions on engine modifications/capability desires.

I'll definitely reach out to 911-hkz

[mysocal911]

Originally Posted by Mr.P 911T 1970

For those who haven't read the article that Thomas provided, it's a must read.

I tried to read it with 3 hours of sleep and looked Greek to me...but now that I have time, whoa...really gives insight on the transformer behavior characteristics between the historical Bosch "black" and the newer replacements. Definitely good variables to consider in making decisions on engine modifications/capability desires.

I'll definitely reach out to 911-hkz

Check for here for Porsche ignition coil data under "Typical Ignition Coil Values"; https://www.systemsc.com/diagnostic.htm

Read here for comparative CDI functional data; http://forums.pelicanparts.com/porsche-911-technical-forum/676385-msd-ignition-exposed.html

[Mr.P 911T 1970]

Thanks, Dave. Appreciate the values and will certainly use these over the next couple of weeks. The biggest take away from the articles you and Thomas provide and lends creditability to Bob, is that the MSD 8222 is acceptable replacement when it comes to reliability and as a "suitable" replacement for Bosch-Black; performance isn't really gained above what Porsche originally intend. I'm getting a longer spark, weaker current.

I'm running NGK5 series spark plugs- would a larger gap support this longer, weaker current. It seems ok now.

Do you or anyone know of a secret hiding spot for the Bosch transformers - the black ones, made in Spain or Germany?

[mysocal911]

Originally Posted by Mr.P 911T 1970

Thanks, Dave. Appreciate the values and will certainly use these over the next couple of weeks.

By chance, do you or anyone know of a secret hiding spot for the Bosch Coils - the black ones, made in Spain or Germany?

Check here; New Porsche Parts, Porsche Restoration, Used Porsche Parts, Rebuilt Porsche Parts, Porsche Service, Porsche Repair, Porsche Custom Fabrication, Porsche Accessories

[Bob Ashlock]

Mr. P, glad to hear you found the problem. That early coil made for traditional Kettering inductive discharge does not play well with the Bosch CDI unit. It produces a weak yellow-appearing spark. Way too much inductance.. somewhere around 7 mH if I remember correctly!

Some things to share from my own experience:

(1) I have never seen an original black steel-can German CDI transformer that has randomly failed in normal operation. (They can be damaged by being connected as a conventional ignition coil.)
(2) Some aluminum-can replacements often have a short life and fail by arcing internally. Many of the shops I do business with report such failures, and I have some dead examples here. They draw current, but nothing comes out the high voltage tower. I was told by one shop that there was a recall. Unfortunately, date codes for the 'bad' ones are not known.
(3) Unpainted aluminum-can Brazil replacements primary inductance is around 400 uH. The original German ones are around 200 uH. This difference is not significant as far as normal operation goes.
(4) Recently one shop reports they are routinely buying the replacements again with no more problems.. newer ones with the problem apparently corrected. But without date code info it's hard to nail it down. These replacements are available from a wide variety of distributors and who knows whether they have good ones or bad ones on the shelf?
(5) Now here's another twist... recently I received a couple of CDI units to rebuild and the customer sent in the coils with them to check. At first glance, the coils appeared to be black originals, but then I realized they were imposters .... aluminum can ones that had been painted black, complete with proper sticker. He bought them that way! So, for a quick check for black imposters use a magnet and see if the can is aluminum. The original German ones are all in steel cans.
(6) So far, aluminum can ones always show the same stamped date code "908", but followed by an additional re-stamped "real" date code. For example, three I have here show "647", "653" and "988". (This was also discussed in the excellent Gerberding writeup.)

[Jonny H]

^ What he said.

There is also another 'imposter' made by Beru. There are black and silver versions but they are longer than the Bosch CDI coil.

Having spent too much time researching into the Bosch Black coil, the reason they are so reliable is mostly down to the black 'tar' insulation that they are filled with. When heated, this turns into a thick oil that is pretty much self-healing in terms of filling any voids / air gaps between the windings.

Have spoken to a number of transformer winding companies and essentially you can't get that black tar anymore - most use a resin or a transformer oil to accomplish the same thing but this requires the bobbin to be wound using different insulation materials - e.g. the design has to be different for a resin filled coil.

I have cut/machined open many failed Bosch silver coils and they fail because they are filled with epoxy. Often 'bubbles' or voids are present in the epoxy which points to lack of or incorrect vacuuming of the epoxy when setting. This is a difficult process in terms of repeatability. Temperature, vacuum and time are all critical.

The next part is speculation. Imagine you were the Brazilian coil manufacturer and you were mainly making epoxy filled 'low voltage' coils and were asked to remake the CDI coil. I would wager you would just use the old bobbin design and just fill the coils with epoxy instead of 'tar'. I very much doubt you would go back and check the the design is suitable for epoxy fill. They get away with it on the Kettering coils since they are not under as much stress.

[mysocal911]

Originally Posted by Mr.P 911T 1970

Thanks, Dave. Appreciate the values and will certainly use these over the next couple of weeks. The biggest take away from the articles you and Thomas provide and lends creditability to Bob, is that the MSD 8222 is acceptable replacement when it comes to reliability and as a "suitable" replacement for Bosch-Black; performance isn't really gained above what Porsche originally intend. I'm getting a longer spark, weaker current.

I'm running NGK5 series spark plugs- would a larger gap support this longer, weaker current. It seems ok now.

Do you or anyone know of a secret hiding spot for the Bosch transformers - the black ones, made in Spain or Germany?

Yes, using coils with higher primary inductance will provide a longer spark pulse width, which allows for a more complete combustion.
As an example, the original small black Bosch coil with a primary inductance of .20mH will develop a spark of about 30us.
When the blue Bosch coil with a primary inductance of about 12mH is used, the spark pulse width is about 140us, over 4X the spark pulse width.
Obviously, it's nowhere near the better spark of an inductive discharge system which approaches about a one millisecond spark pulse,
which explains why all Porsche vehicles now use an inductive discharge ignition system.

[Mr.P 911T 1970]

Thanks for the insight, folks. Bob, you repair my CDI a few years ago and it's working great - thanks again.

I found two other alternatives that I found but they don't list their spec sheets - as far as performance, not sure of likeness. Both are oil filled. The only spec sheet I found was on the MSD 8222 on Holley's site.

First, NGK, p/n U1130: the only added benefit is the 3 year/36,000 mile warranty. But NGK has a good reputation for its plugs...

The second is Wells Vehicle Electronics out of Wisconsion, p/n 5C1381. They provide basics on the can's construction but nothing critical to the conversation of inductance.

I've reached out to both companies for a spec sheet but we'll see...I'll share if I hear something.

[Fred Winterburn]

The bitumen or tar filling of the older Bosch coils seems to last well in moderate to hot climates, but not so well in climates that experience really cold temperatures. At least that's been my experience with older Bosch inductive coils for 60's era Volvos. The coils can fail sitting on the shelf inside the shed without being used. In general I don't trust any old coil, especially German ones. Oil seems to preserve early magnet wire better, but today magnet wire is so well made it probably doesn't matter what you fill the coil with providing it allows for some thermal expansion and contraction of the copper wire and there are no voids. Fred

Originally Posted by Jonny H

^ What he said.

There is also another 'imposter' made by Beru. There are black and silver versions but they are longer than the Bosch CDI coil.

Having spent too much time researching into the Bosch Black coil, the reason they are so reliable is mostly down to the black 'tar' insulation that they are filled with. When heated, this turns into a thick oil that is pretty much self-healing in terms of filling any voids / air gaps between the windings.

Have spoken to a number of transformer winding companies and essentially you can't get that black tar anymore - most use a resin or a transformer oil to accomplish the same thing but this requires the bobbin to be wound using different insulation materials - e.g. the design has to be different for a resin filled coil.

I have cut/machined open many failed Bosch silver coils and they fail because they are filled with epoxy. Often 'bubbles' or voids are present in the epoxy which points to lack of or incorrect vacuuming of the epoxy when setting. This is a difficult process in terms of repeatability. Temperature, vacuum and time are all critical.

The next part is speculation. Imagine you were the Brazilian coil manufacturer and you were mainly making epoxy filled 'low voltage' coils and were asked to remake the CDI coil. I would wager you would just use the old bobbin design and just fill the coils with epoxy instead of 'tar'. I very much doubt you would go back and check the the design is suitable for epoxy fill. They get away with it on the Kettering coils since they are not under as much stress.

[mysocal911]

Originally Posted by Mr.P 911T 1970

Thanks, Dave. Appreciate the values and will certainly use these over the next couple of weeks. The biggest take away from the articles you and Thomas provide and lends creditability to Bob, is that the MSD 8222 is acceptable replacement when it comes to reliability and as a "suitable" replacement for Bosch-Black; performance isn't really gained above what Porsche originally intend. I'm getting a longer spark, weaker current.

I'm running NGK5 series spark plugs- would a larger gap support this longer, weaker current. It seems ok now.

Do you or anyone know of a secret hiding spot for the Bosch transformers - the black ones, made in Spain or Germany?

Can you please describe how you determined/measured (scope/current probe) the "weaker current", as indicated in the above post? Thanks

Yes, the MSD 8222 is a good replacement for the original small Bosch black coil. As linked to in post #6 (maybe missed it), here're the coil's parameters;

MSD Blaster (8222) - R(primary) = 1.1 ohms, R(secondary) = 4700 ohms, N = 95, L(primary) = 4.2 mH, L(secondary) = 38 H

[Mr.P 911T 1970]

Hi Dave,

No I haven't measured the current, I'm going off of Thomas's article that he posted above.

https://www.911-hkz.de/Zuendspulen.htm

[Mr.P 911T 1970]

Johnny, thanks for the tip on the tar substance...

I'm ordering two transformers: MSD 8222 and another which is proprietary. The supplier [omit] provided the data to support a "Bosch-Black" likeness with the tar; the chart data is downloadable once you've purchased the coil from them. This coil is also offered by Stoddard but they don't provide any data that adds value to the converstation.

Zoom in on the side profile of the picture and you will see the manufacturer of the proprietary transformaer. https://www.*************/sic60250201-sic-602-502-01.html

I"ll post my decision on whether I went with the (1) MSD, the (2) 44-year old black Bosch coil, or (3) the new "proprietary" one.

[Mr.P 911T 1970]

Well, l'm lucky then. The donor SC is from Hawaii, so the coil has been hanging out in warm climate it's whole life.

Just compared the temperatures from the new Bosch coils to the original black one, after I drove it the same distance, same load. The original Bosch coil (44-year old) was noticeable cooler (warm) to the touch while the newer Bosch was hot.

[mysocal911]

Originally Posted by Mr.P 911T 1970

Hi Dave,

No I haven't measured the current, I'm going off of Thomas's article that he posted above.

https://www.911-hkz.de/Zuendspulen.htm

Thomas's report;

"The ignition coil BERU ZS-109 can be used, see the following explanations, even if a longer ignition spark (120 µs instead of 27 µs)
occurs here with a lower combustion current due to the principle. Engine test bench tests with overhauled original engines
and engines with moderate performance have not revealed any differences in the running behavior of the engines. Unfortunately,
this coil is no longer produced."

It appears he didn't actually do a measurement, which reduces the credibility of the report.

[mysocal911]

Originally Posted by Mr.P 911T 1970

Well, l'm lucky then. The donor SC is from Hawaii, so the coil has been hanging out in warm climate it's whole life.

Just compared the temperatures from the new Bosch coils to the original black one, after I drove it the same distance, same load. The original Bosch coil (44-year old) was noticeable cooler (warm) to the touch while the newer Bosch was hot.

Why do you over-complicate the issue?
1. The original black Bosch coil is very reliable.
2. The Bosch silver coil is junk.
3. The MSD 8222 is a good replacement for the Bosch black coil.
4. Only by switching to an inductive discharge ignition system will there be any significant spark improvement.

[Mr.P 911T 1970]

I over complicate the issue because I am on night shift...930 pm to 530 am...6 days on....lol

I'll keep you all updated. Thanks again.