PermaTune CDI

[andoni510]

Can anyone recommend where to send 6 pin PermaTune CDI for repairs? Thank you in advance.

[john walker's workshop]

Round file. That one looks like a modified 8 pin. A 6 pin has 2 rows of 3. Was it on an early 930?

[andoni510]

Originally Posted by john walker's workshop

Round file. That one looks like a modified 8 pin. A 6 pin has 2 rows of 3. Was it on an early 930?

Yes, need it for an early Turbo.

[mysocal911]

Originally Posted by andoni510

Can anyone recommend where to send 6 pin PermaTune CDI for repairs? Thank you in advance.

That's the universal PermaTune used as a universal CDI replacement. Do a Google search,
as there're many who rebuild CDI units. Use Bosch CDI in quotes, i.e. "Bosch CDI unit".

[john walker's workshop]

You can use a 6 pin unit if you use a 6 pin plug and put the wires in the proper place. Just did that on my 77 930 because the old 8 pin was dead.

[ischmitz]

Some of the Permatune units are potted, everything internally is encapsulated in a back resin. Those units are not serviceable at all. Even if the unit isn't potted I don't know of anyone of top of my head who would work on these.

In general the 8-pin and the 6-pin units are functionally interchangeable (both Bosch and Permatune). I don't know for sure about Permantune but assume the only difference between the 6-pin and the 8-pin is the external connector. Internally the are most likely the exact same electronics. For Bosch there are fundamental differences internally between 6-pin and 8-pin in the way they charge the main capacitor. The 6-pin uses a continuously running DC/DC converter and makes the distinctive whine, and generates lots of heat in the process.

The 8-pin use an all together different charging scheme. The trigger signal is used to release a pulse of energy that get's transformed and stored into the capacitor. So the box is only active once it "sees" a trigger signal and thus don't whine. In addition the housing of the 8-pin is much nicer, old-school hermetically sealed with a gasket. However, these units command prices in the 1000$ neighborhood if you can find one.

Externally both the 6-pin and the 8-pin take the same trigger input and deliver the same output to the coil (transformer) and tachometer. To use a 6-pin box in your car you either need to modify the existing harness or fabricate a little conversion harness from some spade terminals and wires.

Ingo

[mysocal911]

Originally Posted by ischmitz

Some of the Permatune units are potted, everything internally is encapsulated in a back resin. Those units are not serviceable at all. Even if the unit isn't potted I don't know of anyone of top of my head who would work on these.

The one posted is not potted. The Porsche factory used a PermaTune in the '76 911.
As posted before, many rebuild CDI units and a few also rebuild PermaTunes.
Again, the Google search function is your friend.

Originally Posted by ischmitz

The 8-pin use an all together different charging scheme. The trigger signal is used to release a pulse of energy that get's transformed and stored into the capacitor. So the box is only active once it "sees" a trigger signal and thus don't whine.

Which is how the posted PermaTune (& all PermaTunes) operate.

[timmy2]

If you decide to go 6 pin, there are only 2 wires that need to be joined together (shields/ground) in the original CDI wiring harness part of the engine harness. I can tell you how to do it and either supply or tell you where to buy the correct 6 pin plastic connector housing and terminals for it.
I also can supply the correct rubber boot for the housings. PM or email me.

[rick-l]

Does anyone have a link to a description on how this thing works? It sounds like it is different from a standard CDI.

[mysocal911]

Originally Posted by rick-l

Does anyone have a link to a description on how this thing works? It sounds like it is different from a standard CDI.

It combines an inductive type with a typical CDI output. Energy is initially stored in the
primary of a transformer and then transferred through the secondary to a capacitor,
and then subsequently applied to the ignition coil by a SCR. Ideally no energy is wasted
as is the case when using the typical free-running inverter.

[Jonny H]

Originally Posted by mysocal911

It combines an inductive type with a typical CDI output. Energy is initially stored in the
primary of a transformer and then transferred through the secondary to a capacitor,
and then subsequently applied to the ignition coil by a SCR. Ideally no energy is wasted
as is the case when using the typical free-running inverter.

Interesting. So this all happens off the points trigger? Surely, that would introduce a significant delay unless they use the falling edge? If this is the case, aren't we back to having a dwell time issue? How is this overcome?

The normal boxes are ~20W in 'standby', hardly a big deal so why would they bother with the extra complication?

Maybe something else different as well? I know some had a rev limiter function.

[mysocal911]

Originally Posted by Jonny H

Interesting. So this all happens off the points trigger? Surely, that would introduce a significant delay unless they use the falling edge? If this is the case, aren't we back to having a dwell time issue? How is this overcome?

The normal boxes are ~20W in 'standby', hardly a big deal so why would they bother with the extra complication?

Maybe something else different as well? I know some had a rev limiter function.

Buy one, you'll find it's a very simple design. The design was used in an Audi in the '70s
and by Porsche in the '78 turbo. Porsche also used the same Bosch 8 pin ignition of that
design in the 917 and some later race cars.

[john walker's workshop]

Up to '77 930.

[Jonny H]

Originally Posted by mysocal911

Buy one, you'll find it's a very simple design. The design was used in an Audi in the '70s
and by Porsche in the '78 turbo. Porsche also used the same Bosch 8 pin ignition of that
design in the 917 and some later race cars.

Not exactly easy to come by, especially not for sensible money. Which Audi?

I wonder why they fitted this to the early Turbo only, then reverted to back the standard 6 pin in later years?