MoTeC Global Forum

Hi Folks,

My current setup is getting quite old now and has a 4 tooth crank trigger wheel with a GT101 sensor. Without sounding too stupid, what is the advantage of replacing it with say a 36-1 as I see available now?

Thanks in advance
Steve

HI Steve,

The ECU is able to update the crank position 9 times faster with a 36-2 crank trigger wheel, allowing for greater accuracy of injection and ignition timing events, it also makes the timing less susceptible to timing variations caused by the crank speeding up and slowing down inbetween firing events.

Just watch out that you don't exceed the maximum frequency of the crank sensor pick up.

I know that the GT101 has a bit of a reputation in this area.

Thanks Stephen, that was well explained.

Greenamex2, Is there a more suitable sensor to use in this case?

Cheers
Steve

Hi,

I tend towards the use of a magnetic sensor for use with missing tooth trigger wheels, especially with higher tooth counts, as they just send the signal out, without any filtering that occurs with the hall effect sensors. If a engine comes factory fitted with hall effect sensors and is using the factory trigger wheel, then this is acceptable, as the factory will have specified the sensor correctly (you have to presume!) but most of the aftermarket hall effect sensors are designed for use with trigger wheels that do not have a missed tooth gap (such as wheel speed tone rings) and the missed tooth can cause some issues.

The design of the trigger wheel gap also affects how the sensor reads, with the proper design being that the gap area is not as deeply cut out as the normal teeth, this helps smooth the signal through the gap and stops errors.

What Stephen said...assuming a decent diameter trigger wheel, a solid mounting for the sensor and a nice tight air gap.

On a 10,000 RPM engine with a (from memory) 100mm 32-1 trigger disc any air gap over 1mm would prevent a good enough signal to allow the engine to start plus the engine would misfire much over 7000RPM. Signal quality was also crucial for startup, any poor connectivity or moisture in the connector and forget it.

On my new engine (8000RPM V6) I have the trigger teeth machined into the flywheel (60-2) and am using a Race Technology hall effect sensor initially. I am expecting to have to switch to either a Cherry hall effect sensor or a VR/inductive/magnetic type...we shall see.

Having used both, I would take the RT sensor over the Cherry unit.

Thanks for the info fellas,

To summarise.
Going to a 36-1 trigger wheel is a good idea but the standard gt101 is not up to the task even tho the engine is limited to 6500?

Cheers
Steve

Gt101's don't work well with missing tooth modes due to the internal signal conditioning circuit. Chopper disk material and tooth profile will also affect how well it will work and what RPM it will operate to. Honeywell have that included on their data sheet.

Use a magnetic sensor with the correct pole diameter/tooth ratio, shielded cable. Keep the wiring away from strong magnetic fields and it will be fine.

Find an OEM style wheel and sensor....they've already done all the hard work.