Tachometer for 59AB engine
 

Looking for help to decide on a tach. I have a 59AB in my 1935, with a Mitchell OD and 3.78 rear. I am trying to better understand the RPM at speed. When I run at highway speed without the OD it roars, but with the OD is hums along nicely (easily doing 65 on interstate). I am guessing at the RPMs, but wish to know more accurately. I am not looking for a permanent, installation but just something to tell me what is going on when. Ideas?

Re: Tachometer for 59AB engine
 

Why don’t you just calculate the difference? All you need is the tire diameter or revs/mile, the overdrive ratio and the rear axle ratio, which you already told us. Let us know if you need help with the calculation.

Re: Tachometer for 59AB engine
 

Since you're not looing for anything permanent, how about something like this : https://www.ebay.com/itm/31781209284...3ABFBMkIfQzZZn. I know it's for a single cylinder engine, but since each cylinder fires once per (one or two) revolution(s), it should work for any number of cylinders. There are many types available. At the price, it might be worth a try.