The Ford Barn

kevinshea · 03-03-2026, 09:44 AM

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?

Zeke3 · 03-03-2026, 10:46 AM

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.

tubman · 03-03-2026, 01:02 PM

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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.

03-03-2026, 09:44 AM	#1
kevinshea Member Join Date: Apr 2015 Location: old orchard beach maine Posts: 64	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?

03-03-2026, 10:46 AM	#2
Zeke3 Senior Member Join Date: Dec 2014 Location: Columbus, IN Posts: 1,646	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.

03-03-2026, 01:02 PM	#3
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 12,132	Re: Tachometer for 59AB engine Sponsored Links (Register now to hide all advertisements) 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. Last edited by tubman; 03-03-2026 at 01:32 PM.