MSD connection for twin coil 911 setup - HELP NEEDED

[stv951]

Hello fellow Pelecaners,

we have built a 911SC with 3,2 high compression pistons, ditched the K-Jet in favour of the PMOs and twin plugged the heads.

We use a 964 twin distributor and twin coils with single MSD 6AL PN6425

Can someone with a similar setup help with the wiring connection ?

I used search engine, but i didnt find a sililar setup (964 twin distributors)

can someone elighten me ?

TIA

[sigchuck]

I ran into wiring issues (user error) with my single plug MSD install, but in researching my problem found a few threads on twin plug applications. I think you wire the coils in series:

MSD for Twin Plug

[stv951]

Originally Posted by sigchuck

I ran into wiring issues (user error) with my single plug MSD install, but in researching my problem found a few threads on twin plug applications. I think you wire the coils in series:

MSD for Twin Plug

Thank you

i have seen this setup and tried it but still doesnt work. Can anyone confirm that its the right wiring for my application ?

[jpnovak]

The 964 distributor does not have an internal trigger for timing. How are you sending an input signal to the MSD?

Post some more information about how you currently have it wired and we can provide more assistance.

[Mahler9th]

My 3.8L racing engine was single-plugged for over a decade. It used an SC distributor, an MSD 6A and two MSD Blaster coils. The MSD boxes were wired in series.

We ran single plug due to simplicity-- I did not need the extra power that dual plug enables.

I converted to twin plug in about 2016 when I changed to a racing class where I needed the twin plug power. That set up used the same MSD components, but a modified 993 factory distributor.

I bought the distributor used at a dismantler.

The distributor was then modified to include an SC-styled pickup by my friend/engine builder. The process, which he had done numerous times, took him about 6 hours. This included a belt change. This allowed the MSD set up to get the type of input signal it needs from the 993 factory distributor.

It worked fine initially, but the distributor had a "hidden" issue that was not discovered when it was modified. It failed during a racing warmup session at Sears Point, and the resulting misfires damaged (broke!) the crankshaft. There is a thread on this elsewhere in these forums.

Yes, the misfires broke the crank.

Instead of buying another 993 distributor and modifying it, I bought one of the excellent JB racing twin plug distributors.

When my distributor failed, it got the attention of my engine builder/friend and another friend-- Jerry Woods. His builds used 993 distributors and factory ignition modules-- not MSD. He liked the factory stuff for logistics purposes for trackside support.

Jerry had considered having replacement 993 distributor bearings made as they were not and likely still are not available from Porsche. Instead his customers just bought brand new 993 distributors from time to time as part of maintenance.

I suggest making absolutely sure that your distributor is tip/top.

And I don't think the MSD boxes can fire with a standard 993-style distributor output signal.

[targa72e]

As others have said you cant use a standard 964 distributor to send a signal to trigger the MSD. The 964 triggered the coils from the ECU which got its signal from a sensor reading teeth on the flywheel (same as 3.2 Carrera, 944, etc). It sounds like you will need to modify the distributor or replace it with one that can trigger the MSD.

john

[winders]

I have a 964 twin distributor modified for use with a twin iginition/twin coil MSD setup sitting in my garage that I don't need anymore.....

[Jonny H]

Originally Posted by stv951

...twin coils with single MSD 6AL...

Apart from your triggering issues, that won't give you a very good spark due to reduced voltage and you'll probably lose all the benefits of the twin plug head. You need two boxes!

[Mahler9th]

Dang, Winders has one that will work right now today. I have seen it. I would try to cut a deal for that one and sell the stock one. Then I'd run twin msd boxes and twin blaster coils.

[Mahler9th]

Decided to take greater precautions after my busted crank.

With this scheme, the mag pulses from the modded factory style distributor are sent in parallel to the two MSDS.

Each of those gets power and ground, and can fire an MSD blaster coil. The high vibe ones are potted. The normal ones are not-- they are oil-filled. You choose, but if the latter you cannot expect them to survive if mounted upside down.

If the tach goes dead, you know that MSD box #1's tach signal may be the culprit. And if it is, it might have stopped because the box has a problem.

The tach out of MSD box #2 goes into a ~$40 rpm switch. Set the rpm switch to say 2k rpm. Above that and the NC contact goes to open. Below that it is closed. So above 2k rpm, the dash light is off .

The light comes on below 2k rpm, including zero rpm, which might be seen if MSD box #2's tach output signal goes to zero.

After I made he dwg I decided on an amber color rather than red.

So you have a visual warning if either MSD box output signal goes to zero. Not foolproof. MSD can possibly have failure modes that do not effect tach output. I inquired but they could not really help with that scenario.

I decided that this scheme was easy as I already had the rpm swith installed for the hour meter. And I had an extra amber dash light.

[Mahler9th]

I use this 12 VDC dash light (amber):

https://www.summitracing.com/parts/rnb-84916?seid=srese1&gclid=Cj0KCQiAyJOBBhDCARIsAJG2h5chsRAHWiWJkj9dhEOd frb63zbeev0kIb94Pv7uX4MgHJgAUMfRotIaAryREALw_wcB

I use a similar blue one for my alternator warning light.