Thread: Questions about a Plymouth 217ci Flathead

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Our family had several of the Plymouth six flatheads but before the age where I could mess with them; although I helped my Dad more than once do a "driveway rebuild" where I held the light for him while he tried to rering, scrape (clean carbon) and replace bearings over a weekend and invariably ran into a time constraint to be able to drive the car on Monday morning. I am sure that we included several moths that hovered around the light and got trapped in oil. As I recall the Plymouths we had ('35, '36, '40 and '51) had awesome torque in low gear and then it was over, and that may have been due to the rear ratio but I don't know what those rear gears were. Anyway, it is true that the Ford flathead FACTORY reliefs were shallow but I guess I was brainwashed because every Hot Rod feature car I studied from '53 to '56 or so always had a Ford flathead "ported and relieved". Maybe R Pope knows the limit to mill a Plymouth head? I recall that a Model-A head could be milled up to 0.125" (1/8" !) and would run for a short time before something failed but then the combustion chambers in the Model-A heads are huge and the T heads are like soup bowls! So the question is by the time Mopar got to the last gasp flathead in '54 how much room was left in the "bowl" for a safe cut on the head, .060"? As far as the rering after relieving the block, I would "guess" one should be able to stagger the ring gaps away from the relief? Of course the other advice given above is sensible in going to a shaved head, dual carbs and some sort of headers, but I guess it is a pet idea that I would like to see someone do in using a straight mill cut on a shallow angle to relieve a side-valve engine. I do know that as a kid working in a gas station and moving all types of '50s cars, there was a very noticeable power increase in going from Plymouth, Dodge, DeSoto and Chrysler straight six engines based solely on increasing cubic inches, so maybe someone out there can advise our friend about the maximum safe bore for a 217? By the way the '53/'54 Belvidere body is an unappreciated classic in my mind so whatever you do to the engine, it should still result in a very cool ride!

Don Shillady
Retired Scientist/teen rodder