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Old 12-13-2011, 07:10 PM
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Could use some guidance on MSD dist. mod (to serve as cam angle sensor)

Need to mod a MSD distributor to serve as a cam angle sensor for a FAST XFI system using a crank triggered, sequential inj mode, SBC. So I grind off seven reluctor teeth and have to reposition the reluctor some amount. I believe the remaining tooth will have to be positioned so, when running, it crossed the pickup before the rotor reaches the #1 tower correct? But by how much? How do I measure this? I also understand I'll set things up by installing and rotating the dist so the rotor is on #1 tower with the crank at 25 deg. BTDC on #1 compression stroke. Crank trigger set at 50 deg. Does all this sound right? Hope so. Need that reluctor help. Thanks.

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Old 12-14-2011, 05:38 PM
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Quote:
Originally Posted by Zeeb
Need to mod a MSD distributor to serve as a cam angle sensor for a FAST XFI system using a crank triggered, sequential inj mode, SBC. So I grind off seven reluctor teeth and have to reposition the reluctor some amount. I believe the remaining tooth will have to be positioned so, when running, it crossed the pickup before the rotor reaches the #1 tower correct? But by how much? How do I measure this? I also understand I'll set things up by installing and rotating the dist so the rotor is on #1 tower with the crank at 25 deg. BTDC on #1 compression stroke. Crank trigger set at 50 deg. Does all this sound right? Hope so. Need that reluctor help. Thanks.
Well for starters if you grind off all but one tooth on the reluctor you will have to do so on the pickup coils as well.Trouble is that with only one tooth it may not generate a strong enough signal to register with the fast EFI.
Let me look into some of the system specs and I will see If I can come up with some answers or a solution.Maybe someone else has done something along the same lines and will chime in too.
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Old 12-14-2011, 06:02 PM
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I see they want you to use The "dual sync" dizzy on the application you have.
Except for the fact you want to run yours with the crank trigger on your engine.
I guess you are trying to avoid the expense of buying there distributor.Nothing wrong with that.
I gather from the term Dual sync and the lack of any type of base engine rpm sensors listed in the instructions , the distributor must have 2 sensors in it to run the system.One for crank and one for cam position.
Having a picture of what the dual sync dizzy looks like inside could be a pretty valuable clue in solving how to meet your need.
The cam signal required can be several different things as far as voltage amplitude (or level), Volts time hi, V time lo, positive or negative polarity, and the system can fire at peak voltage or at an ascending voltage or on a rise voltage at a certain threshold,as well as physical orientation to the posistion of the cam are all factors.
. Most are a square wave , using only a blade that passes between a coil and a magnet, pretty simple, but orientation of said blade , length of blade(delgates on and off time) all are important factors. But I have a hunch you knew that anyhow.I will keep looking around.
Some of the early buick 3800 engines used a cam gear with a magnet mounted in it and a sensor in the timing cover.That though crossed my mind , but it still doesnt solve the other tech issues like type of signal and orientation in degrees .

Last edited by latech; 12-14-2011 at 06:11 PM.
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Old 12-14-2011, 06:35 PM
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After looking around, I think you are on the right track with using the GM dizzy and grinding off all but one of the teeth on the reluctor (and pickup coil in my opinion) so it makes one "Blip" on each revolution.
Using a dizzy with an older vacuum advance style may work well, as you could modify the advance part with a screw adjuster( like some of the old european cars used for an octane adjustment) which would allow you to set the dizzy where it fits your intake and still be able to adjust the trigger position to the desired angle of cam positionto be registered
MSD also offers a spark plug wire pickup sensor that would accomplish supplying a signal, but I wouldnt opt for it. You cant adjust the signal timing without changing the engine base timing. and putting all that high voltage next to the wiring for a pricey EFI unit somehow doesnt sound to good to me.
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Old 12-14-2011, 06:45 PM
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Thanks. I gave Comp Cams another call (they own FAST) and this time I spoke with someone who said a standard MSD can indeed be modded to serve as a cam angle sensor. Their verbal instructions:
1) Cut off 7 "teeth"
2) Drill and tap reluctor, installing a set screw that will allow repositioning the reluctor rotationally and tightening to shaft.
Install and set-up as follows:
1) Set engine rotation on #1 compression stroke, set to minimum timing anticipated (the timing that will be commanded by XFI at maximum boost) - In our case this may be about 15 deg.
2) Phase the rotor to tower #1 with crank in position above. Lock down dist. The dist. will not be adjusted again
3) Set crank to 80 deg. BTDC on #1 compression stroke.
4) rotate reluctor to align only remaining tooth with sensor
5) Lock set-screw
6) Set engine to 50 deg. BTDC. Align crank trigger with sensor

Comp said the CAS pulse has to come before the crank trigger pulse. It will in this case, by 30 degrees of crank rotation. The rotor phasing at minimum expected timing (maximum boost point with the most timing "pulled") is simply to ensure good ignition performance (best rotor alignment) when the engine is at maximum effort. They also said the cam angle reluctor adjustment is not critical. I'm having a little trouble understanding why that would be the case. Perhaps its only purpose is to let the ECU know when #1 is on a compression stroke?
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Old 12-14-2011, 06:58 PM
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Cam timing is for Identifying which cylinder is on its intake stroke. It is used to differentiate between any cylinder and its companion cylinder, like cyl 1 and cyl 6 . It is used to keep the injectors spraying in time with the cylinder that is on its intake stroke. As long as the ECM knows the posistion of the cam, it can calculate which cylinder is inhaling next in sequence. Obviously the signal window for that is pretty large, and all firing events , spark and fuel are calculated from engine rpm (crank) signal anyhow.
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Old 12-15-2011, 10:51 AM
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Quote:
Originally Posted by latech
Cam timing is for Identifying which cylinder is on its intake stroke. It is used to differentiate between any cylinder and its companion cylinder, like cyl 1 and cyl 6 . It is used to keep the injectors spraying in time with the cylinder that is on its intake stroke. As long as the ECM knows the posistion of the cam, it can calculate which cylinder is inhaling next in sequence. Obviously the signal window for that is pretty large, and all firing events , spark and fuel are calculated from engine rpm (crank) signal anyhow.
Yep. I ran sequential on my turbo engine with no cam sensor at all. Basically, the ECU just fires injectors in sequence independent of cam angle. I was using VEMS and the consensus with their design group was that other than for fuel economy concerns the cam angle was really not required. I dont know if this is true, but I know that mine worked fine with one trigger.

The thing you have to realize is that the only way you will get the crank and cam position sensors dead on is if you use an oscope, or maybe a meter depending on the sensor, to set them. You have to know if it is looking for rising or falling edge and slowly adjust the sensor until you see on your scope what you know the ECU is looking for. This is because it is impossible to know the exact point at which the trigger/hall/vr sensor is going to "see"(rising edge) the tooth/magnet it is looking for and when it is going to "loose sight" (falling edge). With a scope you can learn this. If it is a hall sensor pulling to ground you can simply measure continuity to ground for this.

What I would do is set the crank at the initial timing, say 22 degrees, and then slowly move the distributor until I saw got a tone on my meter. Then I locked it down. That was usually withing a degree or two when varified with a light.

Last edited by TurboS10; 12-15-2011 at 10:59 AM.
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Old 12-16-2011, 02:51 PM
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There is a Cadilac, I think 4.9L distributor that also had a cam sensor in it.

There's also a 2.5L four cylinder distributor with a cam sensor in it.


I think the best idea for a cam sensor on a distributor that will no longer need the cap because of DIS is what Jeep did origanlly.


Then there's a guy who builds them for LS engines...


Hope that gives you some ideas.
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Old 12-16-2011, 05:32 PM
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The only problem I see here that hasnt been Identified yet is, what type of signal the system the OP wants to run needs for a cam signal. As Turbo s10 said it will either be a VR (variable reluctor) or a hall effect signal.Not to mention if it triggers at leading edge or peak or trailing.
The issue is ...what is the system setup to use, VR, or hall. VR will be two wire and hall will be 3 and will require the unit to supply a reference and ground besides the signal path. Hey maybe it is an Optical distributor they use, with phototransistors and LEDs . All 3 setups have a different voltage capability and signal characteristics.Hmmmm. Sure would like to see the inside of the "dual sync" dizzy that they want you to run.
I was checking a few other tuner sites ( ) and one guy said to take an OE dizzy and grind off all but one tooth on the reluctor, and it would/should work. I am not certain he actually did it or that it worked, but that was the jist of the conversation.
Trouble is, like I said before, if you grind off seven teeth from the reluctor, you still have 8 trigger points on the pickup coil which will pick up the one tooth as it passes over each one on the coil. So you have to take all but one off from both. Then because you have taken away 7 of 8 teeth on both, you get asignificantly smaller voltage generated as you have removed 7 of 8 mechanical pieces that are operating in the magnetic field for the purpose of signal generation .
Fords EEC IV dizzys had the eight blade wheel in them.If you look at it closely, the blade that fires #3 cylinder is only half as wide as the remaining 7 blades. The shorter blip created by the half width blade is how they determine cam position to run the engine in sequential mode.
The engine has to have a definitive way to determine cam angle/position or it cannot operate in sequential injection mode, it can only batch fire , which is not as efficient or performance oriented.without cam angle the ECM cannot accuratley determine which cylinder is at its optimum place for fueling, batch firing is like using a shotgun to kill a mouse, pretty easy and effective, just not Ideal.

Last edited by latech; 12-16-2011 at 05:41 PM.
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Old 12-16-2011, 06:44 PM
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Now see, I think using a shotgun to kill a mouse is just getting the job done

I used an accel efi distributor on my S10 that was a single signal hall. I pulled up some pictures of the dual sinc and it sure looks similiar. I would just about bet it has two hall sensors, but Im gonna keep looking for information.

Edit: Summit list the trigger as a magnetic trigger which from my understanding would be a hall sensor.

Last edited by TurboS10; 12-16-2011 at 07:11 PM.
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Old 12-16-2011, 06:49 PM
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Quote:
Originally Posted by TurboS10
Now see, I think using a shotgun to kill a mouse is just getting the job done
ROTFLMMFAO
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