Which Tacho adaptor

Muscle-Manta · Post by **Muscle-Manta** » Tue Mar 10, 2015 3:20 pm

I am running an MSD 6AL programmable ignition system on my Rover SD1. The Tacho works up to about 4k before flicking about all over the place.

I tried using one of these http://www.summitracing.com/int/parts/msd-8920 to sort the problem. However it didn't work at all..no tacho. As I bought the unit at an autojumble it might have been faulty. Or on the other hand may not have been suitable for my Tacho.

Noticed MSD do at least four other tacho adaptors.

Would anyone be able to help as to which model I need.

Thanks,

Paul.

DEVONMAN · Post by **DEVONMAN** » Tue Mar 10, 2015 3:37 pm

Have you wired the msd 8920 for a voltage triggered tach?

DaveEFI · Post by **DaveEFI** » Tue Mar 10, 2015 5:17 pm

Good luck.

Have EDIS on my SD1, and none of the circuits MegaSquirt gave worked 100% properly with my SD1 unit. Despite others reporting success. It could be there is quite a bit of tolerance across the SD1 units. In the end, I replaced the electronics inside the unit with a modern design.

Muscle-Manta · Post by **Muscle-Manta** » Tue Mar 10, 2015 7:36 pm

DEVONMAN wrote:Have you wired the msd 8920 for a voltage triggered tach?

I tried the voltage triggered first and when it didn't work I tried the other method shown in the instructions. That also didn't work.

Muscle-Manta · Post by **Muscle-Manta** » Tue Mar 10, 2015 7:39 pm

DaveEFI wrote:Good luck.

Have EDIS on my SD1, and none of the circuits MegaSquirt gave worked 100% properly with my SD1 unit. Despite others reporting success. It could be there is quite a bit of tolerance across the SD1 units. In the end, I replaced the electronics inside the unit with a modern design.

That sounds like what I may have to end up doing. Have you still got the original tacho dial fitted to the new internals ?

DaveEFI · Post by **DaveEFI** » Wed Mar 11, 2015 12:24 am

Yes, it's just the PCB - the meter movement stays. I fitted it to the outside of the housing to allow access to the adjustment since there's plenty of room, but could equally well be fitted where the original was.

It's based on the LM2917. It will trigger happily from a 5 or 12 volt tach pulse.

Parts cost is low.

Robrover · Post by **Robrover** » Wed Mar 11, 2015 7:48 am

With a Smith's tachometer, if you are using the white wire into the MSD-6AL you'll need an MSD 8910 tach adapter.

It hangs off the MSD-6AL red and white wires IIRC. I'm running an MSD-6AL
and MSD-8223 Blaster 3 coil, a Bosch based Scorcher distributor with vacuum advance, NGK spark plugs

When I wired it up without the tach adaptor on hard acceleration or above
3000 RPM, the tach signal would wave around and drop to zero. The MSD 8910 fixed the problem.

If you are using the magnetic pick-up input (green and violet wires) to trigger your MSD Ignition, I think you will need the MSD 8920 Tach Adapter.

Muscle-Manta · Post by **Muscle-Manta** » Fri Mar 13, 2015 11:43 pm

Thanks Rob, I'll try the 8910. I am using the blaster 2 coil and an MSD pick up mounted in the rover dizzy.

Cheers

Paul.