Thread: Questions about a Plymouth 217ci Flathead

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I recently purchased a 1953 Plymouth Belvedere 2dr hardtop. It runs good, but I was thinking of rebuilding it as it either has 92k miles on it or 192k miles on it. Either way I was wondering are there options to keeping it stock but basicilly cleaning the ports up and what not? I restore and rebuild vintage italian bikes and I usually polish the ports and open the exhaust a bit, as the original could have been done a bit better. Basicilly match everything up.

So I guess what I am asking any ideas on what could be done to my flathead without making it hopped up???

Yeah, you could rebuild it stock with some tweaking such as hard exhaust seats and stainless valves to tolerate today's unleaded fuels. Here's a source for obsolete parts that I've used in the past.....
http://www.egge.com/about.shtml

Can you recommend a good place to get a pair of lakepipes??

http://www.thehotrodgirl.com/lakepipes.html

Weir Hot Rod Products 4911 Paoli Loop Rd. Napa, CA 94503 ... 1940s, 1950s and 1960s custom accessories, Lake pipes

That little Pilgrim will like a mild port job, and a planed head will liven it up, too.

Yeah, you're welcome welder

Yep, standard old time hop up techniques will pep this old flathead 6 right up. You can mill the head, add a little more carburation, duals or a header, pertronix ignition, have the cam reground, etc.

I think there are still places to buy the intakes (Clifford maybe, or Speedway?) and a couple of two barrel, or one four barrel carb will help a lot. Probably even on Ebay would these show up from time to time.

Don't forget the chrome acorn nuts on the head bolts.

Don

Hey Hey,

I have been busy, but thankls to all with this wealth of knowledge. I cant wait til this winter to start working on her.

Ok will this work......

offenhauser duel intake
TD performance 2bbl carb to 1 bbl manifold adaptor
two 2 bbl Strombergs


Yes? No?

The Strombergs can be made to work, but they don't have the proper vacuum port for your distributor. Two stock 6-banger carbs will work better.
And of course, the aforementioned chrome acorn nuts will be required. (!)
Why don't you want to make it "hopped up"?

www.stoveboltengineco.com sells headders for your flat 6 and intakes also I think, also some nice Holley/ Webber 5200 carbs for $89 each

If you pull the engine for a rebuild and/or to bore the cylinders here is the last word in souping up a flathead (side valve) block. The easy modern way to do this would be to find a milling machine large enough to tilt the block slightly about 2 degrees (depending on the width of the block) with the valve side down and mill out a wide channel from the valve seats to the edge of the bore. If you plane the head too much you will actually choke off the flow from the valves to the cylinder. Yes, a "relief" will lower the compression ratio but increase the flow. This used to be done by hand grinding in a very tedious artful way. The problem is that there is no easy way to make the reliefs the same volume using hand grinding since you can't cc the results easily. Thus I am giving you this old picture from a 1951 paperback to show how a modern milling machine might do it. Some of the later flathead Ford V8 engines had factory machined reliefs in the block but having shown you this I am not aware of anyone who has used a milling machine to do this accurately. Note the depth at the edge of the cylinder bore should not cut into the water jacket or go below the top ring on the piston at TDC, but maybe 1/16" to 1/8" is possible. Actually most of this art was applied to flathead Ford V8s but it should work for any side valve engine. I guess if I were doing it I would worry about cutting into the water jacket and limit the depth to 1/16" and/or look around for some diagram of a cut through Plymouth block to make sure there is enough metal on the top of the block to allow such a cut. OK so you say this is not necessary but if you plane the head too much you will actually reduce the flow over the "hill" between the valves and the cylinder. On the other hand if you know where there is a large milling machine with a bed to mount the whole block and you can work out the extra cost, all that is needed is a straight cut from the valves to the bore without all the tedious hand grinding. If you do this send us some pictures and tell us the approximate extra cost beyond a usual rebore. Hey I spent my whole career in "Theory" so I would like to know if anyone out there has done this using a milling machine rather than a hand grinder.

Don Shillady
Retired Scientist/teen rodder

The factory reliefs on Ford flatheads was done to reduce the thickness of the metal in this area and reduce the tendency to crack the block, due to uneven expansion. Any extra flow was more than offset by the reduction in C.R.
Rounding the corner at the top of the bore will gain some flow, but the extra hassle involved when re-ringing the engine makes it questionable.
Most flatheads work better with aftermarket high comp. heads, but a Mopar 6 can be planed without any problems.

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

Maximum safe bore on any motor will be determined by sonic checking of the cylinder walls. You need 0.135" thickness after boring, honing, etc. You could determine how much the head could be milled by removing the head and stacking some modeling clay on the valves, then bolting the head back on and turning the motor over with a socket/handle. Then remove the head and measure the thickness of the clay. I'd say that if you had 0.060" on the intakes and 0.080" on the exhausts clearance between the valves and the head, you'd be ok.