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Old 10-29-2021, 10:26 AM   #8
DailyDriverMods
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Originally Posted by 142 guy View Post
Are you doing sequential injection and coil on plug (or similar) or are you just doing timing control in MS3 and retaining the conventional coil and distributor?

Something to consider in repurposing an old distributor to provide a cam position signal is wear on the distributor shaft. On my B20E, wear on the distributor shaft contributed to significant timing wander at 3000 crank RPM. Volvo used to sell distributor rebuild kits through GCP which allowed you to re bush the distributor. This worked as long as the distributor shaft itself is not worn, although getting the split pin out of the drive end of the distributor shaft to allow disassembly can be a challenge.

If you are going with coil on plug or a similar arrangement which eliminates the need for the distributor function, consider the Yoshifab adapter to mount an optical cam angle sensor in place of the distributor on OHC redblocks. Gives you both a cam position signal and a medium resolution (12 crank tooth equvalent) tach signal. That was my solution for dealing with a worn distributor shaft although it is significantly more expensive than the $30 Hall sensor. Clearly does not work if you need to retain the spark distribution function.

As bobxyz notes, the Aliexpress part looks like a Pertronix clone. Eliminating the centrifugal and vacuum spark control by locking the breaker plate to do spark timing control via MS3 is trivial. Modifying the plastic collar to give you a single pulse per distributor revolution may be slightly more challenging. If you don't need the distributor function, you are relatively free in figuring out the positioning of the trigger. If you need to retain the spark distribution function of the distributor then life is more complex. I don't know about MS3; but, on MS2 the recommended positioning is to have the cam position signal occur about 60 deg before TDC on #1. Getting that 60 deg timing with an unmodified breaker contact plate and still retaining reasonable alignment of the distributor rotor with the contacts in the distributor cap can be a challenge.
I'm currently using the dizzy in combination with an MSD 6AL / Blaster II ignition system which is driven by the megasquirt. The megasquirt uses the crank sensor and an ignition map to determine the timing. The sensor in the dizzy would only be used to sync up the fully sequential mode, the timing itself will be determined via the crank sensor.

I think i'm going to try to make it work with the Volvo hall sensor dizzy. If this doesn't work out with the cam signal timing being too close to TDC, i can always use the Ali express sensor and maybe custom 3D print a new plastic collar.

A full-on cam trigger with a pattern wheel would be a bit overkill for just syncing up the sequential signal i think.
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