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Discussion Starter #1
Hi guys,

I'm looking for some advise on a crank trigger solution. I had a look at the various solutions where the trigger wheel being installed either behind the pulley damper or on the crank gear :


(the gaps are quite large I would machined smaller gap/tooth).

As I want to keep things closed to OEM look, I've been thinking to have the pulley damper machined with correct tooth size if the tooth would be on the pulley damper.

If the trigger wheel is fixed to the sprocket it bothers me the trigger wheel would make the pulley damper pushed foward. Is this safe ?
Except if the trigger wheel is only 3mm width I guess that could be ok.

Speaking of width .... the width will be dictated by the crank sensor.
I looked at them (hall or VR). Honeywell makes new units that look very interesting (I haven't consider the GT101).
Basically the sensor serie SNDH-H https://sensing.honeywell.com/sensors/hall-effect-digital-speed-sensors/SNDH-H-series (hall effect) requires a wheel of 2 or 3 mm.
What worrying me is the rumour of the lack of reliability for hall sensors (anyone experienced a hall effect failure ?). Where as the VR won't fail.
A lot of choice (too much ?) in VR sensors : https://sensing.honeywell.com/sensors/industrial-vrs so I don't really know what to choose.
ECU will be a Haltech Elite 2000.
Both VR and hall effect sensor have very similar max frequency (15khz so enough for a 36 tooth wheel @ 9000rpm) and both are rated to work in 150°C environment.
One advantage of the trigger wheel fixed to the sprocket is that it can be replaced with another wheel to accept a new sensor where as if you machine the oem pulley damper this may not be possible.

In the end I can't decide what path to take : VR or hall, pulley damper machined or trigger wheel on the crank gear.
 

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VR sensors are harder for ECUs to read if you care about things like that.

If you look at how the OEMs do it, the crank gear has a trigger wheel mounted to it usually. There's probably a good reason for that.

I personally would not chance a crank sensor being slightly off, your ECU has no way of verifying that the crank sensor is set up correctly in most cases and has to trust the signal. If the crank sensor slips only a few degrees you can end up with overly advanced timing.
 

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I used the GT101 hall sensor for both the crank and cam triggers on my R34 GTR with RB30.

For the crank trigger, I used the cap heads of the clutch retaining bolts through the back of the flywheel.

I also put little magnets inside the cap heads to increase the response just in case the flywheel was to flex.

The large diameter of the flywheel makes for a very accurate position.

For the cam trigger, I made a pointer that bolted to the cam and mounted the GT101 inside the standard trigger disc housing, it was completely invisible.

Had a look for photos, but could not find them just now, but think I have some somewhere.
 

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Very interesting topic.Really like the idea of using the flywheel method, been looking at similar coming from Alfa Romeo V6`s.
I would not go with the std damper as machined above, look at how much the dampener outer ring moves back and forth. I reckon in that case Id stay with the std CAS.

The 24 tooth trigger attached to the lower belt gear would be first choice. Fixed to the crank without any movement from rubber dampeners.

Look at "cherry" hall sensors, made for wide variety of uses. Always used Hall sensors , mostly OE Bosch ones, in all my projects.
 

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Discussion Starter #10
I asked about the type of sensor because when you search it seems that many japanese manufacturers choose the VR type for their sport cars when using a crank trigger wheel (Toyota, Honda at least). It can't be wrong thus.
Having the OEM pulley damper CNC machined is an interesting option but with smaller tooth to have a better accuracy (the bigger the wheel the more tooth needed to achieve same accuracy).
 

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I asked about the type of sensor because when you search it seems that many japanese manufacturers choose the VR type for their sport cars when using a crank trigger wheel (Toyota, Honda at least). It can't be wrong thus.
Having the OEM pulley damper CNC machined is an interesting option but with smaller tooth to have a better accuracy (the bigger the wheel the more tooth needed to achieve same accuracy).
Few things to consider with VR vs hall effect:

1. VR is highly sensitive to noise, especially on the signal wires. You are using an analog signal and the circuits analyzing that signal are not magic, the ECU realistically can only do some plausibility checks to reject noise and maybe a low pass filter. When I worked with VR crank sensors it was absolutely necessary to form a twisted pair on the wires and cover it with shielding grounded to the chassis.

2. One method of rejecting noise is having a minimum trigger voltage to register as a tooth. VR sensors produce different voltages at different RPMs. This means that your sensor will be less robust at lower RPMs, if the battery voltage is slightly lower than usual you can end up with an engine that cranks but the ECU won't sync the ignition signal because it's not seeing any crank sensor pulses.

3. VR sensors are more tolerant of heat, so it can operate in conditions that hall effect sensors can't. But they are extremely sensitive to the gap set while hall effect can tolerate misalignment/air gap changes to some extent.

4. VR sensors are kind of a pain to figure out exactly where on the tooth you are because a memoryless system would not be able to determine at a given instant whether you are at a trigger edge or not. You have to look back in time to see whether your filtered signal derivative is still positive. Lots of signal processing headaches to think about vs a simple square tooth digital signal.


In my experience VR sensors are most often used because it made the physical engine simpler/cheaper and left a lot of the complexity to the ECU. In single cylinder engines you can have the alternator and crank sensor all in one if you use VR, and both of those things can be in the crankcase which makes it less likely to be exposed to FOD.
 

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Machining tolerances are a big part of the accuracy that you can achieve with your trigger wheel.

Bigger diameter is good, since it reduces the angular effect that the machining tolerance applies.

The GT101 was the standard Motec trigger sensor for many years - may still be for all I know, it has an internal magnetic bias that assists in identifying the presence of the trigger wheel / or not.

My R34 GTR was good for over 155MPH on the 1/4 mile, I believe the GT101 was an important part of that performance.
 
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