Unless you are “physically” challenged or have space limitations in your frame, I would stay away from ANY auto trans behind a Flathead. It is my understanding that all automatic trans have a certain amount of slippage or power loss due to their design and a stick shift has a more positive “lockup” than an automatic. You are already down in the h.p. Department when running a Flathead, so why hinder it further with an automatic trans. Been building flatheads for 60++years and have never considered an auto trans. Have always had a heavy foot and ran my flatheads pretty hard and gave up on the 39 style trans and banjo rear ends back in the 70’s. Changed to a built up Muncie and or GM 5 spd and nine in rear so that I will never break these components no matter what kind of ridiculous behavior I sometimes exhibit. IMO a hot rod needs 3 pedals if possible. My 32 Henry cabriolet (sold it went to NewZealand) ran 80 mph in the 1/8 with a 5 spd and 3:89 Detroit locker but ran 2:75 on the street and 70 mph was only 1900 rpm. Flatheads Forever!!
The Jalopy Journal
