dimented24x7

iTrader: (2)

Im going to be running a later model vortec PCM and SFI on my older block. Normally with a flat tappet, this wouldnt be an issue as I could use the stock vortec TC cover, trigger wheel, and sensor. BUT, I have an aftermarket roller cam setup, so the plastic vortec cover is out of the picture.

I've been thinking of maybe using an aftermarket magnetic trigger wheel with an inductive pickup. My question is, though, how much does the signal amplitude/timing vary with these setups as teh engine RPMs change? Are the pulses stable, or does it tend to drift around due to the "AC generator" effect? The waveform shape isnt as much of an issue as I can use some circuitry to generate a pulse thats compatible with the PCM, but if the pulses start coming sooner as the engine speed picks up, it'll throw the timing and injector firings off and even set a DTC if its bad enough.

Also, is there a standard polarity for the magnets in the wheel? Like, do all the field lines point north or south, or do they just randomly bonk the magnets in? I'm trying to get a hall effect pickup from crane, but I dont think it will happen. MSD makes a hall effect pickup that could be adapted, but it will only trigger with the proper magnetic orientation.

Apeiron

You'll be using the zero crossing, so there won't be any problems with amplitude.

doc221978

This may sound stupid. Since the vortec is already a roller, wouldn't it be easier and cheaper to just get a cam ground for it, that allows use of the front cover? Or maybe adapting the vortec peices to a metal cover? It seems like it would just take a drill and some patience.

dimented24x7

iTrader: (2)

Good point. With that said, I would assume that there is a polarity to the magnets then? In other words, I can expect to see the same waveform for each cylinder reference pulse? It would seem to be that way if you wanted to trigger on the falling edge of each pulse. If the wave starts out positive, then I could just trigger when it goes slightly negative. That would be the zero crossing (or near to it).

Edit: Now that you have the little wheels turning in my head... It would seem that a simple schmitt trigger with the proper negative trigger threshold would be all that would be needed.

dimented24x7

iTrader: (2)

That thought had crossed my mind. Maybe just using a modified stock timing set and trying to weld in a bung for the sensor. But, it requires a good deal of precision to place the sensor. Its feasible to just add degree bias' for the injector and igntion firings if the placement of the sensor is off, but there are other subtleties as the crank trigger pulse is the prime mover for the software code in the PCM. Much of the software code is only run when a crank trigger pulse is recieved and the computer calculates the fueling on the fly, so precision is important. Id also like to try to just use existing off the shelf parts to minimize the ammount of fabrication needed.

doc221978

Just a thought. I always have an easier time with the mechanical side. If I tried all the programming and everything you were doing..... the engine would never run.

Apeiron

All the magnets on a given setup will be the same. The polarity of the magnet determines which direction the zero crossing goes.

dimented24x7

iTrader: (2)

Ok, so its safe to assume that they're either all south facing out or all north facing out?

Apeiron

It's safe to assume that the waveform will be the same on every crossing.

dimented24x7

iTrader: (2)

Yeah, Im still keeping that option open. I'm contemplating picking up a stock cover and sensor to see what kind of effort would be needed. My other thought was to possibly use an external custom 4-tooth wheel.
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Cool. So then it would be just a matter of flipping the wires on the sensor to get the desired direction for the external schmitt trigger.