Would this work?

Could I purchase a pertronix ignitor, which is a hall effect sensor upgrade for the dizzy, and modify this to provide the interval of signol the system needs? The pertronix module mounts in the dizzy, and there is a plastic ring that mounts to the dizzy shaft with magnets at 0, 90, 180, and 270 degrees. I'm thinking this ring could be taken appart and re-made to match the magnet mounting instructions in the SDS manual. If the ring can not be used, perhaps the rotor from a standard ignition system could have the top part removed, so it was just a plastic ring with a keyway, and a plastic disc bonded to the remaining rotor-ring, and on this disc could be mounted the trigger magnets, in the proper orientation.

I don't see why this wouldn't work, except for any difference in the rpm of the dizzy vs the actual rpm of the motor. They are driven at the same speed, right? The accuracy of the system constructed this way would not be as high as a true crank mounted sensor, as there would be some gear lash between the cam and the dizzy shaft, and the dizzy bearings may have some wear, but for ease of install, this sure would make this already user friendly product much more so to the type 4 guys.

I've posed this same question to the guys at SDS directly, but wondered what you guys thought?

I have some doubts. Remember 2 revs of the crank for 1 rev of the cam.

Dave

Hi Dave,
I did a little research this morning. To understand how Hall Sensors work...here is a pretty good summary.

Hall Sensor

The problem I see with the petronix is the signaling modification. Effectively the petronix is duplicating the action of the points. It contains a hall sensor and a trigger wheel just like you would need. However, it takes the signal from this sensor and uses it to activate a relay that provides the on/off action for the coil.

This works perfectly in this situation, but I believe the SDS system is designed to plug directly into a hall sensor. I believe the on/off action of the petronix system is not what the SDS system is "looking for". A normal hall sensor will produce an change in voltage potential between two terminals when it is activated/deactivated.

Looking at the SDS website. The "F" version of the system contains a hall sensor in the kit. I think this would be the best method because the output of this sensor would be compatable with the SDS system.

I've got a couple old distributors around that we could cut up, Since the distributor turns only once for every rotation of the crank, you would just have to put twice as many points on the signaling wheel to duplicate the signal as it would appear via the crank.

Finally, I'm not an electrical engineer so if anyone can comment on this please do!

This won't work.

First, the SDS system expects to see signals at crank speed, and expects to see a TDC signal on each cylinder pair (for a four cylinder), so there are two TDC magnets. With the Pertronix ring, it would still see a magnet at each TDC. This part is OK.

Second, the SDS system also expects to see a signal 40 degrees BTDC on cylinders 1 and 4, from a second Hall sensor. This tells the ECU which cylinder pair is about to fire. To get this with your proposal, you'd need a second Pertronix in the distributor, which only reacted to TWO of the six magnets you'd need to install (one for each TDC, one 20 degrees before cylinder 1, and another 20 degrees before cylinder 4). 20 degrees is smaller than the width of the Pertronix, so getting the signals timed correctly wouldn't be possible, as the sensors would have to overlap somehow.

You COULD do this with your own Hall sensors and your own magnet ring. Hall sensors can be set up to be triggered by either the north or south poles of a magnet, so if you point the two extra magnets so their south poles point out, and the four TDC magnets so their north poles point out, the Hall sensors will only "see" the magnets they're supposed to see. The sensors are small enough that you can position them close together.

The problems you face here are fabricating a sturdy enough setup mechanically (lots of vibration here, which is bad for electronics and soldered connections), and one that can handle the enormous amount of electrical noise inside a distributor.

Yep, it won't work with a Pertronix.

It could be made to work with something custom, but you lose the advantage of removing the slop of the dizzy....one of the main points of going to crankfire.

See below for what I got back from the folks at SDS today. Oh well, it was an interesting thought...




Hi David,

This might be a better bet, stock dist and J&S which other air cooled
Porsche guys have used before.

Cheers,

Ross




David Parsons, RSG wrote:

> Thanks for the snappy reply. Given that there is no "easy" axcess to
> either end of the crank, any suggestions on what might work
> best/easiest. I'm not afraid to tear it all appart, but would rather
> spend my time driving and racing than wrenching, if there is an easier
> way.
>
> If this crank thing just looks too problematic, my plan "B" was to use
> your fuel only system, and go with either a stock dizzy, or maybe
> mallory, and run a J & S safeguard ignition retard system. If this is
> a system you're not familier with, check out: aircooled.net, and
> search the word "safeguard". Have you folks had any experience with
> this unit?
>
> David
>
>
> ----- Original Message ----- From: "Ross Farnham" <sds7778@telus.net>
> To: "David Parsons, RSG" <ottox914@charter.net>
> Sent: Tuesday, April 25, 2006 9:55 AM
> Subject: Re: would this work or not with your systems?
>
>
>> Hi David,
>>
>> Our hardware would have to be mounted on the crank somewhere.
>> Distributor mounting is not recommended due to technical issues with
>> magnet positioning and dwell time.
>>
>> Cheers,
>>
>> Ross