a bit of evidence around the problems of nissan cam based triggering

[RICE RACING]

1 hour ago, burn4005 said:

Yes, I think that's now accepted wisdom. The point of this thread is to show some evidence as to what is happening, and how bad it actually is.

I could put up if owner allows the end effect on knock and ign advance, we are talking 'allot' at 8000rpm and on-wards.

You also see it graphically when trying to run a VR sensor on a single tooth on the cam, it can trigger errors due to the slap in the belt (again if your ECU reports this?), its one of the easiest way just do a sync capture and check the wave pattern, it is horrendous !

So you go from running maybe your target ign timing on one cylinder at one cycle and could be out multiple crank degrees on another cycle, and again on a top quality knock control system you will see this as we did, change out the ghetto trigger system and much more safety and much more power is to be had

[iruvyouskyrine]

I'm not as smart as most of the people in here commenting but i do have a question, the 'sync position' on the Emtron is that just a measurement how far out of alignment the cam 24+1 'sync/home' signal is with the crank based 'ref/crank'.

Is it comparing the 'sync/home' trigger event to the same 'ref/crank' trigger event every time? If so then even though the update speed is nowhere near the same as the crank based pickup it should still give a good indication of how much variation is being induced in the cam driven setup correct?

Also what is the accepted 'minimum millisecond pickup time per tooth' for a high revving engine such as an RB? There seems to be such a large spread available especially in OEM form (Evo having 2 crank teeth and LS having 60-2) yet all engines seem to run fine. But in the skyline aftermarket world people will argue anything from 6 - 60 teeth on the crank are required. Looking through your maths @burn4005 it seems that 5deg/tooth @ 8000rpm = 0.000391ms is an absurdly small amount of time it could be considered overkill. I understand that if your hardware (ECU and crank pickup assy) is up to the task the more finite the triggering the better, but i guess my question is what is the minimum amount of teeth required to result in smooth engine operation and effective and reliable ignition timing (not needing individual cylinder knock control like RICE is talking about)

[burn4005]

that is correct,

the sync signal occurs only once every two revolutions of the crank, and the edge of it occurs between the same crank teeth on every sync event. the edge always occurs in the 10 degree window between 300 and 310 (of the crank wheel), so it drifts around by a few degrees. so what you end up seeing is the cyan trace moves slightly to the left and right as the belt stretches/cam to camshaft coupling wobbles.

This is why when you get to high tooth counts (60 tooth wheels) you always run a missing tooth on the crank so the reset is done based on that, as if you don't have a missing tooth you are telling the ecu to do the reset on the next crank tooth after a sync signal. and if that sync is wandering by 4/5 degrees you're in danger of the ecu taking the wrong crank tooth as the crank reset. with 12 tooth crank, the gap is plenty wide (30 degrees) so you can be sure the sync will always occur between the same teeth. 

the upper limit of time per tooth depends on the response of the sensor (my crank sensor (ZF GS101205) will do 15khz under ideal conditions, the only other limit is how small a resistance you use for the pullup. (15khz is 75000rpm on a 12 tooth crank, or 15000rpm on a 60 tooth crank) the falling edge is always very steep as it is a low impedance short to ground by the sensor (open collector) and thats why you should always use it as a trigger edge as it is much more consistent. The rising edge starts to look like a shark fin as it takes some time for the voltage to rise again after the short to ground stops. A 1k ohm pullup will rise much faster than a 4k7 pullup. so at very high speed it might not make it all the way to 5v before the hall triggers again.

 

Shark fin:

 

In a good ECU this isn't a problem as you can set the trigger voltage threshold, so as long as the trigger signal rises to say 2.2v, then falls to 0 it is counted as a trigger event. I am using the internal 4K7 pullup in the emtron and don't have a problem at 8800rpm, I scoped to to confirm voltage rise was fast enough to get well beyond my 2.2v threshold, otherwise I would have used a 1k external pullup instead.

the earlier sensors (GT101 etc) had an issue with the Schmidt trigger design which is required so the hall effect trigger thresholds are self adjusting. So if you had missing teeth it could cause issues as there was a very sudden change in event spacing time. the newer sensors (like my ZF one) don't have this issue. its also very important to have as small an air gap as you can to force the hall effect voltage hysteresis gap size in the sensor to be much wider, which also helps to avoids false trigger events. mine is only ~0.4mm from the trigger teeth. If you have a large air gap, it is a weaker signal so the Schmidt trigger needs to be more sensitive so you have a larger chance of false trigger or missed trigger events.

Hall sensors are fine, as long as your tooth pitch (spacing), height  and depth match the requirements of the sensor. the more teeth, the bigger diameter you need.

a company called Spectec make extremely high performance hall sensors that can cope with tiny tooth pitches where a Cherry just wouldn't reliably pick up teeth. (like trying to make a 36 tooth hi-octane style kit)

 

a VR sensor doesn't have any of these issues, and the faster the trigger wheel goes the better the signal to noise ratio gets as the signal amplitude increases. it also crosses zero as the trigger point which provides perfect accuracy, rather than an arbitrary 2.2v which isn't as precise as you're relying on "catching" a falling edge that isn't perfectly vertical.

 

Edited September 18, 2018 by burn4005

[iruvyouskyrine]

Thanks for the excellent in depth response. I understand that you have to match the frequency response of the sensor to the tooth frequency/RPM of the crank to ensure everything is operating within its correct parameters, but my question is still what would you consider the minimum teeth on a crank trigger wheel to give effective triggering on an RB? 

What exactly is the crank trigger kit you are using?

[burn4005]

on an RB26 12 teeth is plenty as it is operating at high speed when ignition timing is important ( and at high speeds the errors are less) under boost/load 1 degree makes a magnitude more difference than under vacuum). it depends how important rock solid idle timing is to you (we are talking ~1-2 degree error though).

on a slow revving, high torque high compression engine (diesel for example) where the power strokes are slow and strong you would want more teeth. 36+

I went a 36-2 as i like the engine starting one crank sooner and my engineering OCD got the better of me.

my kit came from JHH racing, they weld either a 12 or 36-2 wheel to a 1000hp ATI balancer and supply a sensor and bracket that bolts to oil pan flange. excellent bit of gear.

 

Edited September 19, 2018 by burn4005

[RICE RACING]

36-2 with VR on crank here and HALL on phase (cam) single finger, is faultless where as earlier trials especially on action on limiters (rpm limit especially) would cause lots of harmonics in cam belt and poor signal pattern on cam.

[iruvyouskyrine]

This excites me greatly, new platinum 36-2 crank trigger setup. should be an absolutely rock solid setup, i can't wait to get one.