Food for thought, camfire ignition system?

[GTIspirit]

I've been trying to figure out if there is some way to install an aftermarket/standalone/programmable ECU on say a VW with CIS-E, aka, KE-Jetronic. The limiting factor seems to be the lack of a meaningful timing signal. I'm sure someone could configure MS to use the camshaft signal in the distributor, but that signal only comes from a four window hall effect sensor, greatly hindering accuracy of the ignition system. The rules expressly prohibit crankfire ignition systems, but what about "camfire" ignition systems?

So I'm wondering, would it be allowed to replace the four window hall effect sensor with say a mini 36tooth wheel? And replace the hall effect sensor with a sensor that would read the toothed wheel? The rules say this on the subject:

"Any ignition system which utilizes the original distributor for

spark timing and distribution is permitted. Internal distributor
components and distributor cap may be substituted.

"

I suppose the intent of the rules was that the distributor could be replaced with one of similar function but from a different supplier, like Meyle and Febi parts for example. But the rule does expressly say the "Internal distributor components.... may be substituted." The function of say a mini 36tooth trigger wheel is similar to the function of the four-window vane inside the distributor. And the function of an inductive sensor is equivalent to that of a hall effect sensor. The signals are functionally equivalent, it's just that one has a lot more resolution and a gap at TDC, but otherwise the signals are the same in that they are just pulses read by the ECU.

I realize that the camshaft rotates at half speed, so a 36 tooth camshaft wheel is equivalent to an 18tooth crankshaft wheel, and there are physical limits to how small a toothed wheel could be made and still have the inductive sensor read the gaps.

I'm sure it is prohibited due to some flaw in my logic because I'm prone to creative interpretation of the rules. But I'm wondering why not so I'm throwing this out there for the discussion.

[joeg]

I think what you propose is legal since distributors are free but the accuracy (non-crank sensor) is a big technological hurdle.

[shwah]

There are a lot of people that run VWs on Megasquirt using the 4 window hall signal.

It will be no less accurate than the current ignition, but you can map it.
Yes the timing will 'walk' a little bit with rpm, but again, you can map it to compensate.

The bigger issue has been controlling the fuel side of CIS-E in a more sophisticated manner than WOT enrichment. Been working on it for a while, and IMO there is a solution, but I am not convinced that it is not better to just use Digifant hardware and make it simple to integrate an aftermarket ECU. I am converting my car with DIYAutotune's help, and will have some data on area under the curve for both setups to compare.

[jlinfert]

There are a lot of people that run VWs on Megasquirt using the 4 window hall signal.

It will be no less accurate than the current ignition, but you can map it.
Yes the timing will 'walk' a little bit with rpm, but again, you can map it to compensate.

The bigger issue has been controlling the fuel side of CIS-E in a more sophisticated manner than WOT enrichment. Been working on it for a while, and IMO there is a solution, but I am not convinced that it is not better to just use Digifant hardware and make it simple to integrate an aftermarket ECU. I am converting my car with DIYAutotune's help, and will have some data on area under the curve for both setups to compare.

I think I've gotta argee with you Chris, given my choice I'd just do a digi conversion.

[jlinfert]

I've been trying to figure out if there is some way to install an aftermarket/standalone/programmable ECU on say a VW with CIS-E, aka, KE-Jetronic. The limiting factor seems to be the lack of a meaningful timing signal. I'm sure someone could configure MS to use the camshaft signal in the distributor, but that signal only comes from a four window hall effect sensor, greatly hindering accuracy of the ignition system. The rules expressly prohibit crankfire ignition systems, but what about "camfire" ignition systems?

So I'm wondering, would it be allowed to replace the four window hall effect sensor with say a mini 36tooth wheel? And replace the hall effect sensor with a sensor that would read the toothed wheel? The rules say this on the subject:

"Any ignition system which utilizes the original distributor for

spark timing and distribution is permitted. Internal distributor

components and distributor cap may be substituted.

"

I suppose the intent of the rules was that the distributor could be replaced with one of similar function but from a different supplier, like Meyle and Febi parts for example. But the rule does expressly say the "Internal distributor components.... may be substituted." The function of say a mini 36tooth trigger wheel is similar to the function of the four-window vane inside the distributor. And the function of an inductive sensor is equivalent to that of a hall effect sensor. The signals are functionally equivalent, it's just that one has a lot more resolution and a gap at TDC, but otherwise the signals are the same in that they are just pulses read by the ECU.

I realize that the camshaft rotates at half speed, so a 36 tooth camshaft wheel is equivalent to an 18tooth crankshaft wheel, and there are physical limits to how small a toothed wheel could be made and still have the inductive sensor read the gaps.

I'm sure it is prohibited due to some flaw in my logic because I'm prone to creative interpretation of the rules. But I'm wondering why not so I'm throwing this out there for the discussion.

I agree with your rules interpretation but a 36-1 wheel that small would be iffy as MS seems to have a hard time whe the teeth get really close. We had problems losing rpm signal with a 5" 60-2 tooth crank wheel above 6000 rpm on our GT cars but a 4 1/2" 36-1 works fine. HOWEVER, MS2/Extra code supports a 12-1 tooth wheel and lets you choose if it is cam or crank speed so that could be made to work

[Flyinglizard]

Seems like you can run a trigger on the cam wheel itself.
IMHO. MM

[shwah]

Do some research into motorcycle stuff. IIRC some of them run trigger wheels in small spaces. Not huge tooth counts, but better resolution than the hall sensor wheel.

[jlinfert]

Do some research into motorcycle stuff. IIRC some of them run trigger wheels in small spaces. Not huge tooth counts, but better resolution than the hall sensor wheel.

Actually we are already looking into have some small diameter 12-1 tooth wheels made. Cad file was sent to the mfr, we are just waiting for the protos.

[GTIspirit]

Seems like you can run a trigger on the cam wheel itself.
IMHO. MM

But then how to get the sensor? Someone previously noted that there is no allowance to add sensors, hence me wondering if the wheel could be put inside the distributor and the hall effect sensor on the distributor changed out for an equivalent sensor that can read the pulses from a toothed wheel. But if the wheel could go on the camshaft and and the addition of a sensor was allowed then said wheel could have more teeth.

[jlinfert]

But then how to get the sensor? Someone previously noted that there is no allowance to add sensors, hence me wondering if the wheel could be put inside the distributor and the hall effect sensor on the distributor changed out for an equivalent sensor that can read the pulses from a toothed wheel. But if the wheel could go on the camshaft and and the addition of a sensor was allowed then said wheel could have more teeth.

Our idea is to replace the stock distributor pickup sensor with one that can read the toothed wheel. Using a wheel on the cam is a no go in IT unless one is already there.

[shwah]

Jeff - I would be interested in that part.

[Flyinglizard]

I use a digi dist, with only the module, for a fixed timing on our ministocker. The timing is set at 31 * advance. The timing does not move over 1 degree, ever. Less than 1 degree really. I have used this for 2000 laps or more, never had any problems or failures. I have two modules mounted, but never had to use the other one.
The engine is 12 to 1, runs from 4800 low end to 7300 upper. 100 octane fuel.
What could be improved upon? You are still limited by the dist/belt/shaft twist. Enlighten me. Do I pick up some torque with less lead at 4800?
TIA.