Food for thought, camfire ignition system?

[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.

[shwah]

I run fixed timing on my car as well, but with the 4 window wheel, and have not had issues. I would still be interested in the 12 tooth wheel to test and compare. Not convinced that I need it at all, but don't know unless I test it.

[GTIspirit]

I don't think the stock system has fixed timing, at least not on my '87 16V, unless we mean something different by fixed timing. I believe the Triumph Adler knock box has some kind of electronic ignition advance map. So while it's "fixed" in that I don't believe it can be changed via calibration or EEPROM or chip-tuning, it's not fixed in the sense that there is the same advance at idle as at 7000rpm. The only change that can be made is to rotate the distributor, which will make a global offset to the ignition map.

Correct me if I'm wrong, but the way I think the ignition system works on the VW's with KE-Jetronic, (KE-Jetronic is only for fueling control) is that the knock box contains some kind of ignition advance map. And said map can be retarded in case knock is detected, but said map can never be advanced electronically, only by rotating the distributor. I believe what happens is that the hall effect sensor is in effect a trigger wheel. A pulse from the hall effect sensor goes to the knock box. The knock box knows the engine rpm, and depending on the engine rpm, sends a trigger to the TCI-h ignition coil, which in turn sparks the correct cylinder through the distributor. So there is a delay time between the signal from the hall effect sensor and to the ignition coil. This delay time would be greater at lower engine rpms, and at higher engine rpm's, with more advance, the delay time would be reduced, according to the map.

Now I'm not an engine calibration engineer, but I'm told by someone who is, that there will be a lot of scatter in the spark when the input signal from a four vane hall effect sensor. The four window hall effect sensor simply doesn't provide enough resolution to accurately control the spark timing, and there will be a lot of variance relative to say a 36 or 60 tooth crank trigger. But even a 12 tooth camshaft trigger would be better than a four window/tooth. I'm also told that the spark advance map has a greater effect on engine output than the fueling, that 1-2* difference in timing can make a difference, especially in the all important area under the curve.

So, the way I understand the rules is that whatever will fit inside the stock distributor is fair game. But the stock method of spark distribution must be retained, so the cap and rotor must still be used. There will be some hardware limitations to advance based on the length of the rotor edge, but I would think the four window hall effect sensor is more of a handicap. So if someone has designed a 12tooth wheel to fit the stock 16V distributor they should offer it for sale.

Now about the comment about belt stretch/variance between the cam and crank. I suppose this is why all the OEM's use a crank trigger wheel for timing, the camshaft is only used for synchronization. But still, a 12 tooth trigger wheel on the camshaft is better than a four window vane sensor, and maybe 12 teeth is the resolution limit, above which the effects of the timing belt are noticeable. I don't know, it's a good question.

[shwah]

I know that the knock box has ignition mapping in it. I run fixed timing on my car. I found that the knock box was altering the timing when I did not want it to, and felt that it was an additional failure point that I did not want to leave in the system. My car is wired per the CIS-E Golf without knock sensing diagram in the Bentley shop manual.

The 4 window sensor provides enough resolution to control the spark timing for every single CIS-E/KE-Jetronic car that VW sold. I found that the 'scatter' of the spark timing reduced dramatically when I removed the knock box from the system.

I'll define 'better' between 4 window and 12 tooth setups with empirical testing for my car, as the better that I care about is one that impacts the performance/reliability of the system, and we may just not need the higher resolution.