Another crazy Magnum SMPI swap idea. Crank position sensor location.

[DionR]

Some may remember a thread I started about trying to find a way around the crank pickup problem while trying to swap the Magnum SMPI stuff onto the motor in my 4 speed Duster - http://www.forabodiesonly.com/mopar/showthread.php?t=78887 .

I'm still trying to work around this problem as I don't want to have to go to a 143T flywheel. So, I had decided that I was going to relocate the crank pickup to the front of the motor at the pulley by putting holes in the barrel shaped area of the crank pulley similar to what the flexplate has, only on a smaller scale. The problem with that idea is that it will require a pretty sophisticated mount for the pickup as there really isn't a good surface to mount it to, plus the pickup would be in the way of lots of things on the front of the motor (water pump, etc.).

So, I've been debating about trying to mount something to the end of the cam, where the fuel pump eccentric would be if I was running a mechanical fuel pump. At first I had just thought about running a stock Magnum pickup, stuck in the hole that the fuel pump would have used in the timing cover (with a plate to seal the hole and mount the pickup), but I didn't like that idea as it seemed like a difficult place to keep oil from leaking from. Plus, I wasn't sure how I would build a ring to mount to the end of the cam with the holes in it to match what the flexplate has.

Today I started looking for some other pickups that I might use, and found that a Gen III Hemi uses a crank position sensor that appears to be a hall effect pickup similar to what the the Magnum PCM would need to see. From looking at how the Hemi works, it appears that maybe I could do just a flat plate (similar to what the Hemi has bolt to the crank), spaced off the cam sprocket, with 16 notches (because the cam turns at half the speed that the crank does) cut in the circumference, and the Hemi sensor stuck through a tube so that the o-ring seals it. It is much more complex that that, but that should get the idea across.

The only other trick is that I want to use a Magnum timing chain cover so that I can swap the serpentine belt setup onto the motor. The problem is that cover doesn't have a fuel pump mount and hole, so it would require additional machining.

Anyone have a late model Hemi that they could take some measurements off of for me? Need to know how long the sensor is, from the retaining tab to the end of the sensor, and how thick the ring is on the crank that the sensor reads.

Am I completely nuts? ](*,)

I will try and post some pictures tomorrow that might help with the visualization.

Thanks.

 

[POS Dakota]

Yes, you're nuts with all the work you'd be making for yourself. lol

Here's a visualization for ya...

We've been working on whipping this up for a while.
Bolts on right between the balancer and crank pulley.
You can use a pickup from a place like DIY autotune, or rig up something with the factory CPS since it works on the same principle that one does...

You can have it powdercoated whatever purdy color your heart desires.

Try making your own...diameter doesnt matter. Just get the notches spaced right with a little math and make sure nothing close will cause any interference.

 

[POS Dakota]

As a sidenote, this wasnt whipped up for the purpose of replacing the flexplate found in early 90ish vans with auto trannies....it was for the purpose of being able to put whatever trans you wanted in without worrying about it since now you can even put a GM 6 speed auto behind one with an electronic standalone controller which is a slick *** setup!

 

[DionR]

Yep, that's what I was thinking about on the end of the cam, but maybe a bit smaller in diameter, and more notches.

Hadn't thought about a flat plate like that until I started looking at the Hemi. That would be much easier than machining holes in the barrel of the crank pulley.

My concern with your's is that it will push the crank pulley out of alignment with the rest of the pulleys on a serpentine belt setup. Probably not an issue with a traditional v-belt arrangement (easier to fix the mis-alignment), but seems difficult with serpentine belt. That and I would still have to find a way to mount the sensor in an area that is tight, and far from flat.

One issue with a cam mounted setup is that the plate would need to be adjustable to account for the possibility of degreeing a cam, and I'm not sure how you would get it set as it is behind the cover when the sensor is available to line it up.

 

[DionR]

Looks like the Hemi sensor uses the same input voltage as the Magnum one, so I don't think it will be an issue to use. Both appear to use a 5.0 volt output from the PCM.

 

[POS Dakota]

Right.
What got this going with me was how bad the factory magnum crank sensors suck. They suck to get to when they die, they suck because they DO die, and with the flexplate and sensor your transmission choices are limited. Some people want to use GM or even ford AOD trannies behind their heavily boosted magnums and this facilitates that.
Also makes tweaking the timing a reality. That 46re trans is a piece of ****. I've been through several and I hate them with a passion. I'm giving it one last chance, then I'm going with a cope 727. But I like the idea of being able to put any trans in there that I want with that crap out of the way. I also like the fact that the other options are usually quite a bit cheaper than a 3200 dollar piece of ****. lol

Pulleys...they can be spaced with a washer or something, It's not really a problem.
Use the water pump like the one in my avatar. it has a bolt on pulley. There are even provisions in the hub to use a washer on each bolt hole to space it out a bit.

I dont know what the variable is, but on that same engine (which is carbed) I needed a spacer just about as thick as that plate to properly space out the crank pulley.

I am using a pro products damper and a scat crank. I dont know if my issue will be repeatable but to use that wheel it's a good issue to have.

If you wanted to, you could have a steel pulley machined down and welded to the wheel for proper spacing too...just an idea. It would of course have to be properly located, but that would work too. You could also have the end of the balancer hub machined down a tad to make up the difference. Lots of ways to skin a cat.

But it will work the same as the flexplate. that I guarantee. Doesnt matter what the diameter is. All that matters is that the notches are the right size and in the right degree locations relative to the crank. with a pickup that is adjustable it becomes a lot more forgiving though.