Will a 6 cylinder Rev counter work on a 4 cylinder engine?
Is it possible to recalibrate the face of the rev counter to what the 4 cylinder is actually reving?
I can use my timing light's rev counter to see what the engine is reving.
What about a direct 4:6 recalibration of the face.

It will work, but will obvioulsy only be reading 66% of the actual RPM. You could recalibrate the face, but it would be neater to recalibrate the circuit inside.

It's usualy fairly easy, sometimes there is a small trimmer that you can adjust the calibration with, though it won't always have enough range. Failing that you need to locate the resistor and capacitor that determine the monostable pulse width and change them (usualy either make resistor 4/6 or original value, or capaciot 6/4 of original value).

I've modified and calibrated a load of old Smiths tacho's, it's not that difficult. However, you do need something to calibrate it against afterwards (idealy signal generator and frequency meter, but a known good tacho could be used).

easy way to check calibration on car is to use an osilloscope to get a reading of ignion lt pulse frequency.

I would like to recalibrate the face as it is showing Red Line at 5K. Way too low for a 4 Cylinder.

Thanks

There might be converters available.
Many years ago I manufactured small devices to make 4 cyl rev counters work with V8 engines (on TR8 conversions). A similar type of device should be possible to match a 6cyl rev counter to a 4cyl engine.