A lucky eBay find: NOS SWB Coil

[mike curnow]

John

I have two Bosch coils with the number 0 221 114 006, then a Bosch Symbol (I think) and 007. Is this the 1966 coil you are talking about? Neither has much of a sticker. I also have a Bosch coil 0 221 102 061 12V It has a tin foil sticker that says " cad discharge system" any info on this one.

Mike

[304065]

Mike,

When I mean an '006, that is a Bosch 0 221 102 006. The Bosch usage list is not very clear on the 114, maybe a mercedes coil from the 1970s? On the 0 221 102 061, this is a 08-68- (garbled) usage coil-Bosch says it's for the 911T. Can you post a photo of that one? The T didn't use a CDI, and the Germans didn't call it "cad discharge" so I wonder what that's all about.

[mcampuzano]

. .

[304065]

Now THAT looks great. I will lay a piece of paper over the original and mark the locations of the letters and send it to you. I guess mm for units?

I can't remove the NOS one, it would destroy it (and how would I be able to compete with all the perfect repro stickers? )

[304065]

Added Pertronix stats to the archive.

[gled49]

I wanted to move this thread to the top. This I know about electricity, +,-, and 500ma is 1/2 amp I think. Great info, trying to absorb it. Between Kettering and CDI, Porsche used a Transistor ignition in limited production cars like the 911R. A system M.B. used as well with a different box but with the same Bosch part number. Loren called it an Inductive Discharge Ignition. Any info/help in understanding how this fit in or how it worked. Gordon

[304065]

Gordon,

Yes, this is the elusive finned black box that some people have discussed. It's basically a transistorized electronic ignition that switches the coil.

Recall from the other thread that the max current limit for points is about four amps-- more than that and they burn up for a handful of reasons. Bosch, and others, figured out that if you use a transistor to switch the current you can switch more amperage, without the issues associated with points "bouncing" (or multiple open-close cycles).

If you use more amperage to charge the coil you can charge it faster. Without going into all the math, the more amperage and the LOWER inductance, the more energy is built up in the coil at the first time constant. You can sort of infer that from the difference between, for example, a Bosch Blue coil and a Motronic coil-- the Blue has high resistance and lots of inductance-- would be great for a slow-revving 4-cylinder VW motor, for example, where there is plenty of dwell time to charge it.

On the other hand, a six-cylinder motor like ours doesn't have that much time to charge the coil, particularly at high RPM. By the time a big coil charges and discharges, the next cylinder has already come around. The practical effect is that the coil energy just doesn't get that high, resulting in weak sparks, right when you need them most: High RPM.

How did the Factory cope? Porsche took the conservative route: in 1969 they retained the points, but only as a trigger for the CDI, and with only 420mA running through the points, they would last a long time. The sacrifice with CDI was the extremely short spark duration-- even though the CDI charges the capacitor and dumps it into the little CDI 001 coil with plenty of time to spare, the sparks are so short that you're at risk of misfires depending on load, mixture, etc. But it generally worked well, and in 1978 the Factory went to a magnetic reluctor triggered six-pin CDI to eliminate the points entirely. This is, by the way, the reason that the CDI coils have such small primary resistance and are so physically small-- the coil doesn't store energy, it's just a transformer to step up the 350V voltage output of the CDI up to ignition level. You actually do not WANT a bunch of resistance, I think it would be BAD if you used a Bosch Blue coil with a CDI, might burn things up.

Coming full circle-- remember that I said if you use more amps you can charge faster. Well, with the advent of transistorized electronic ignition, Porsche gave up on CDI in 1984 when it was integrated into the control unit for Motronic. These can switch on the order of 10 amps (don't quote me on the source). This allowed Bosch to charge up the coil faster and still generate enough ignition energy to reliably light the mixture with fewer emissions-causing misfires.

So that's that's all the box is-- a big transistor with an even bigger heatsink attached. Probably done in the days before CDI as an attempt to switch the coils faster to avoid high-RPM low ignition power.

The M-B folks show it like this:



So that's what it is and how it worked-- as far as its usage on race cars, it's just a footnote-- I've only seen a couple photos of those boxes over the last 10 years or so-- I keep wondering whether they will turn up in some other Bosch application, like a Volvo or something, but they are quite rare.

Hope this helps.

epilogue:

With the 964, Bosch moved the coil switches off-board, to a separate "igniter" like a BIM 124, looks like this below. They are even smaller and better and more reliable today-- these are found in junkyards all over the world. THIS is what Bosch was after with that old box in the 911R-- but it took twenty years of semiconductor development to get there.

I have a few of these and the matching coils and a plan in my head. . . but it will have to wait until LONG after Parade 2013. . .

double epilogue:

Today we have inductive pencil coils, which fit on top of the plugs-- with six individual coils, there is plenty of time to charge even a small coil to an energy level high enough to reliably ignite the mixture AND do it in a way that doesn't misfire and push unburned hydrocarbons out the pipe. For REALLY high RPM applications (think sportbikes) there are Pencil Coils that are CDI-- they are actually driven with 90V input from a CDI ignition. When we start hacking coil-on-plug for 911 motors, this is the limitation-- easy enough to find coils that fit down on the spark plugs, hard to find a box to charge them. It can be done, just time. . . and lots of money.

[718RSK]

Checking in on this thread. Curious to learn if the decal has been reproduced yet?

On another note the 006 coil appears to be the the new Bosch part number equivalent of the TK12A10 coil. This coil was used on all 12 Volt 356 era cars including the 904 and C2's. I am not sure when Bosch phased in the new part number but am sure that most/all 901's and a bunch of the early 911's likely had the TK12A10 coil and not the 006.

[304065]

RSK, a I haven't ever seen any references to a TK coil being used on the six cylinder Porsches. I do see them in the Bosch literature for four cylinder applications here and there however.

Here is the page from the Bosch original equipment list-- showing, for example, that my '66 was equipped with an 026 which is electrically the same, except for flat terminals instead of stud/faston.

[718RSK]

Attached is the Bosch table for assigning the new ten digit part number to the old coils. I am not 100% sure when the change to the 10 digit part number was made but believe that it was somewhere in '64. Brad are you out there? As such any 12 volt car made in '64 could have been fitted with the TK12A10 coil.

JK