The V8 Owners Forum -

Pal in the SD1 club wants to fit an MSD unit to a Vitesse with a DLM dizzy. Personally, I can't see the point - but does anyone know if the VR sensor in the DLM will trigger the MSD unit OK?

If anyone has done this and has a wiring diagram, it would be a big help.

I guess the point is that you get a much stronger spark and you get multiple sparks on top of that, when I went from a standard system to an MSD there was a big difference in the engine performance especially above 4.5 RPM.

I think that the standard Lucas trigger would probably fire an MSD unit but the issue is which way round do you connect the wires up, if you connect them incorrectly you will trigger the MSD on the leading edge of the spike which is not correct, it should trigger as the pulse decays on the trailing edge.

I run a Lucas dizzy to fire my MSD and I have setup at least three other systems in the same way but the big BUT is that I removed all of the guts from the Lucas system, I made my own back plate and mounted an MSD pickup on the plate, I still used the standard Lucas spike wheel but it has to get very close to the MSD pickup in order to trigger the system. The dizzies that I have modified in this way also have no advance system at all because I use a programable MSD system, you can basically dial in any curve that you like via the software. It might be possible to fit an MSD pickup into a Lucas dizzy and retain the bob weight system but you would need to be handy with your tools and a good metal worker to do it! You could trigger the MSD off the crank I suppose!

Why is he not using the amp that the DLM normally activates to drive the MSD via the white trigger wire? The amp will be more reliable driving the msd unit compared to driving the primary circuit of a coil.

I've looked at the various circuits MSD provide, but none really cover an injection car with a dizzy where the ECU tach signal comes from the coil negative. MSD do say nothing else must be connected to their coil negative.
They do provide a tach output for a rev counter, but that won't drive the rev counter on the SD1, so would need an adaptor.

Of course all these things can be worked around - but not that easily if you're not too confident at such things.

The circuit they give for European cars does show and amp on the dizzy, so that would be the more obvious one to follow. However, the DLM amp is a known trouble spot, so if it were me I'd prefer to ditch it. Although if no longer driving the coil, it might be more long lived.

MSD state that you should not drive the tacho from the coil because they put about 350v across the coil (and at low RPM it is a multiple pulsed signal). The MSD tacho output will drive a standard SD1 rev counter up to about 5k RPM, after that for some reason or other the rev counter drops to 0 RPM

The SD1 rev-counter can be tricky to drive to work as normal. I know this from EDIS on mine.

If MSD does really produced multiple sparks, there would presumably be multiple pulses at the coil negative which would confuse the tach?

DaveEFI wrote: ↑

Fri Jan 18, 2019 9:51 am

The SD1 rev-counter can be tricky to drive to work as normal. I know this from EDIS on mine.

If MSD does really produced multiple sparks, there would presumably be multiple pulses at the coil negative which would confuse the tach?

The MSD systems do produce mutliple sparks at low RPM, there is a youtube video where a guy puts an oscilloscope across the MSD LT, you can see the multiple pulses at low RPM.

I think that MSD (the company) would be in court pretty quickly if their product did do what is says on the tin....Multiple Spark Distribution.

The rev counter output of the MSD is OK but like you said it does seem to cause an issue with the SD1 rev counter. It was on Paul F H's car that we had an issue. I'd be interested in knowing how you solved the problem!

Dave below is Sidecar's modified DM8 Distributor with MSD trigger as fitted to my 4.6.



The SD1 tach worked up to around 4.5k then goes to zero! Paul.

Please note that the dizzy was 'locked out', it has no bob weights because the MSD unit has the advance curve programmed into it.

This is the pick up https://www.summitracing.com/int/parts/ ... /overview/

Dave, in your opinion would the use of this https://www.summitracing.com/int/parts/msd-8920 solve the Tacho reading problem on my SD1?

The SD1 tach is connected to the coil negative - common practice in those days. Due to the inductance of the coil, there is a large flyback pulse generated - something like 50v peak. The SD1 tach input circuitry is designed with this in mind. The tach output from the MSD unit - and others - will be no more than 12V by nature. More likely 5v.
One way is to make a high voltage generating adaptor, to produce high voltage from that low voltage tach output. Common way is to switch an inductor with a transistor to generate a high voltage pulse. Many use the coil taken from an ordinary 30 amp car relay as the inductor, which costs not a lot to build, as a suitable transistor is pennies.
I assume that's the way commercial adaptors work, but I've no experience of them.

I actually changed the electronics inside the SD1 tach for a modern purpose made chip, which allows it to be adjusted to spot on. Easy on the chassis type SD1 tach, unlike an all enclosed one.

Muscle-Manta wrote: ↑

Fri Jan 18, 2019 4:57 pm

Dave below is Sidecar's modified DM8 Distributor with MSD trigger as fitted to my 4.6.


The SD1 tach worked up to around 4.5k then goes to zero! Paul.

As a matter if interest, did you first try the VR sensor fitted to the Lucas DLM dizzy? You can get at the connections to it by removing the amp. They are standard small spade connectors.

Years back when I tried using Mallory setup it would not work when using injection as it would not trigger successfully. Century Performance said they had seen it working but could not supply and details of customers with it working. Then they brought out this

https://centuryperformance.freshdesk.co ... structions

The below has copied from the MSD manual...

The MSD Ignition features a Gray Tach Output wire that provides a trigger signal for tachometers, a shift light or other add-on rpm activated devices. The Tach Output wire produces a 12 volt square wave signal with a 22.5° duty cycle

sidecar wrote: ↑

Sat Jan 19, 2019 12:30 pm

The below has copied from the MSD manual...

The MSD Ignition features a Gray Tach Output wire that provides a trigger signal for tachometers, a shift light or other add-on rpm activated devices. The Tach Output wire produces a 12 volt square wave signal with a 22.5° duty cycle

Thanks for that. It explains why it won't drive older tachs like on the SD1.Which expects to see more like 50v.

If the SD1 tach used a more conventional PCB, it would be possible to modify that for a smaller signal. But it uses some weird system.