Re: Anyone install an MSD on their Howell TBI??
I hope I'm not jumping in out of turn, not knowing about the Howell, but this may help.
As far as the MSD vs HEI etc - the HEI & Fords are Kettering ignitions, the MSD isn't. The Kettering types apply power to the coil, charging the magnetic field up - storing lots of energy in it until it's needed. The module stops feeding the coil at the right time, the field collapses and generates the high voltage. The tach signal is based on the "open" or no current side of the primary's square wave.
The MSD, a CD, does just the opposite - it stores the energ in the big internal capacitor, it uses the coil as a transformer. So the "open" side of the primary pulse is AFTER the spark. The tach signal needs to be taken from the "on" side of the pulse if it's to be used for injection triggering, else it's way too late.
And since it's firing multiple times, the first one should be tho only one "seen", otherwise it will probably multiple fire the injectors.
That filter is most likely changing polarity as well, that's why the filter for MSD's is different.
EST - The pickup coil does not move with electronic timing. Yes, the spark release is actually "predicted" in order to advance the spark. It's based on the last several pulses that tells it when the next one should occur (I've heard last 7 pulses.) The RPM is determined from those last pulses from the pickup coil, then a pulse timing circuit "predicts" when the next firing should occur.
If I remember correctly - on the GM HEI (7 pin) that pulse timing circuit is inside the ignition module itself. The EST line only tells it to "predict or not," That's the external brown wire. That's the only thing the ECM has to do with it - EST or not. It's not a pulse, just an on/off line.
On Ford systems that predictor circuit is inside the Computer module, not the ignition module. That "predicted" information is sent to the ignition module in the form of a square wave - that pulse simply triggers the on/off firing of the module just like a direct feed from a pickup coil.
Now how/which signal the Howell needs is beyond me.
But it makes me wonder - if the injection system is based on the tach signal, then it must advance as the R's increase? The faster it goes, the more lead time on the squirt?
If so, basing the tach signal on an immovable pickup coil won't advance it? I wonder how important that lead time is for the injection.
Just some thoughts - hope it helps.