Electronic rev counter...

[Oxford Jack]

Not quite along the lines of the previous correspondence but closely related. I have a Durite 52mm electronic rev counter in my trials car, the gauge reads 0-8,000 rpm. On the back of the instrument there is a switch for 4-6-8 cylinder use.
My question/s: if I change the switch to 8 cylinder, will it read at 50% of the revs? or is there a tech savvy reader who knows how to make the full scale read up to 4000 rpm, so that it suits the engine speed rather better than at present?
I could then remove the front and pointer, print a new face reading 0-4,000 rpm and have a more suitable instrument for my purpose.
Here is hoping!