G4+ speed sensor inputs

[klutched]

Hey guys, currently running factory abs/speed sensor on the pinion of my S15 diff in my R33. Have used a factory 2 wire sensor and wired it up to my G4+ GTR plugin into a digital input. Get speed readings fine but am only getting readings to 130-140km/h. 

Have just counted and have 24 teeth on the pinion. It's setup on a 275/60r15 (28.2" roughly).

Does the it just max out the frequency hence why its not reading over 130-140km/h? 

Whats my best option to fix this? I'm planning on putting an abs hub on the front to pick up my front undriven wheel speed so I can setup up a traction control strategy. I believe they are 46 teeth and I will be running it with a cherry sensor. I believe I'll have to grind the teeth down and have it as 23 teeth but unsure if this will just result in the same outcome topping out around 150km~. 

Thanks

[Adamw]

If there are 24 teeth on the pinion and the diff ratio is say 3.5:1, then that is equivalent of 84 teeth at the wheel.  Way too much for the G4+ DI frequency limitation of 500Hz.   One of these will divide the frequency by 8:  https://shop.vems.hu/catalog/hall-p-162.html

[klutched]

5 hours ago, Adamw said:

If there are 24 teeth on the pinion and the diff ratio is say 3.5:1, then that is equivalent of 84 teeth at the wheel.  Way too much for the G4+ DI frequency limitation of 500Hz.   One of these will divide the frequency by 8:  https://shop.vems.hu/catalog/hall-p-162.html

Hmm yeah ok, would it still be the same even if I used a cherry sensor? I assume then if I use the abs pickup on the half shafts and bring them down to a 23 tooth setup would be ok being after the diff gears? 

[klutched]

Ok so I've decided to use the ABS pickup on front and rear with cherry hall sensors. They are a 46 tooth ring so I will need a frequency divider for hall sensors. 

Can anyone recommend one?

[Adamw]

 

[klutched]

On 8/15/2021 at 6:04 PM, Adamw said:

If there are 24 teeth on the pinion and the diff ratio is say 3.5:1, then that is equivalent of 84 teeth at the wheel.  Way too much for the G4+ DI frequency limitation of 500Hz.   One of these will divide the frequency by 8:  https://shop.vems.hu/catalog/hall-p-162.html

Was doing some thinking/calcs, I run a 3.69 diff gear which would mean 88.56 counts per tyre rotation. So when I move the pickup to the axle with 46 teeth per tyre rotation I will get almost double the speed (1.92x). 275/60r15 circum. is about 2233mm, 500hz/46teeth=10.87 rotations per second. 10.87 rotations x 2233mm=24272mm/second = 87.38km/h. Doesn't seem right when I get 140km/h atm with the 24teeth on the pinion.

[Adamw]

The 500hz limitation we quote is very conservative, it depends how many other interrupts various other functions are using.  In a typical basic install they will often go to about 1500hz.   

But something like a 8cyl sequential setup with 8 channels of knock, individual cylinder fuel trims, 4 vvt cams, 4 wheel speeds etc will have less capacity.