Cam Trigger Wheel Review

[Jim_W]

I have a trigger wheel from a VAG 2.0 FSI (AXW) in the stock location, but it has 4 teeth. Two are ~15 degrees wide and two are ~65 degrees wide.
A picture of the stock wheel:


My plan is to mill most of the teeth away and leave a 15 degree tooth with a rising edge at 117 cam degrees/234 crank degrees after cylinder #1 TDC and a falling edge at 132 cam degrees/264 crank degrees after cylinder #1 TDC. See the new part overlaid with the original part here:


My understanding of the cam trigger is that it needs to happen before the spark event for cylinder #1. If the spark advance is set to 30 degrees, the rising edge of the cam trigger happens 51 cam degrees/102 crank degrees before spark and falling edge happens 36 cam degrees/72 crank degrees before spark.

Is this sensible? I just wanted someone double-check my homework before I started cutting metal.

[Jim_W]

Pics not embedding for some reason.

Original, stock cam trigger wheel: https://ibb.co/SQzs6M4

Revised wheel: https://ibb.co/xf4qvQM

[jrussell]

What's the application? Does your crank trigger have missing tooth? Have you tried just filtering the cam sensor rather than resorting to cutting it? The trigger settings in VEMS are incredibly flexible, and every case I've seen so far, can work without modifying the trigger wheel.

[Jim_W]

The application is for ignition using individual coil over plugs. The crank trigger is the standard 60-2 wheel and sensor.

I have not tried filtering the sensor. I will search the wiki for direction on this.

In the case that I want to change the trigger wheel, is the pattern described above suitable? My main concern is the number of degrees the rising or falling edge needs to happen before the spark event.

[jrussell]

Looks like on that wheel the rising edges are 90 degrees apart (that would typically be falling edge on a hall sensor signal).

So you'd want to set the hall sensor to rising edge in VemsTune. Then do a triggerlog.

You should be able to see a value in the triggerlog results where "Ignore sectrig pulses above" can be set and it can use the first "wide" tooth after the missing tooth on the crank sensor. The value would be 22 if the missing tooth is at TDC, but it's probably not, so I can't tell ahead of time.

Your modification should work just fine, but it's not needed in my opinion.