I made some logs this summer and realized that when my cluster indicates 100 km/h my power fc reads 93 km/h. the car is a jdm fd3s with (4.30 gear). Is there a setting for this or is it mechanicle?

 

Mechanical and electronics.
Best to borrow a phone with GPS data or portable GPS for a car to test with.
Run about 10 miles on a flat straight road for the test.

My FD has .806 5th gear, 3.909 diff, with 255/40-17 tires.
My results with a GPS were: speedometer at 70 is really 71, at 80 is really 82.
Odometer reads 4.2% low.

I never rely on the PFC for speed or compared since GPS is more accurate.