rrunnertexas Posted October 8, 2021 Report Share Posted October 8, 2021 The engine in my 1935 Plymouth PJ has engine code P11 meaning it is from a 1941 Plymouth as I understand it. I am wanting to replace the cylinder head as it has lots of pitting and does not look that great, plus I would like to put on a head that has been milled a bit to raise the compression. Reading a bit it appears that a .050" cut is a way to get a bit more, but not sure how much. Since flathead motors are new to me, I'm asking those with the knowlege if the pictured cylinder head that is for sale would fit the bill. It does have "PJ" cast into the head, meaning it is from 1935? Anything in particular to watch out for when installing? Thanks in advance! David Quote Link to comment Share on other sites More sharing options...
Bryan Posted October 8, 2021 Report Share Posted October 8, 2021 Here's info I gleaned from different sites and different people. None of it is mine...just copied into a WORD document. Took a screen shot. Quote Link to comment Share on other sites More sharing options...
rrunnertexas Posted October 8, 2021 Author Report Share Posted October 8, 2021 Bryan - thanks for that info. The head sould be essencially the same for the 201, 218 and 230, correct? Looks like .050" is a safe number to get compression into the upper 7s. Quote Link to comment Share on other sites More sharing options...
Bryan Posted October 8, 2021 Report Share Posted October 8, 2021 1 hour ago, rrunnertexas said: Bryan - thanks for that info. The head should be essentially the same for the 201, 218 and 230, correct? Looks like .050" is a safe number to get compression into the upper 7s. I would think so except it seemed to vary with later year heads. I was going to go with .04 myself...seems like a safe number. Quote Link to comment Share on other sites More sharing options...
Veemoney Posted October 8, 2021 Report Share Posted October 8, 2021 Follow the link to a thread on this site with info for head milling and compression ratios. There is a chart in it that provides info for years and makes. Cylinder head grind - Mopar Flathead Truck Forum - P15-D24.com and Pilot-house.com 1 Quote Link to comment Share on other sites More sharing options...
Sniper Posted October 8, 2021 Report Share Posted October 8, 2021 Don't forget the internal/external bypass differences in the heads. 1 Quote Link to comment Share on other sites More sharing options...
Jerry Roberts Posted October 8, 2021 Report Share Posted October 8, 2021 9 hours ago, rrunnertexas said: Anything in particular to watch out for when installing? That used head could have already been milled down . Quote Link to comment Share on other sites More sharing options...
rrunnertexas Posted October 9, 2021 Author Report Share Posted October 9, 2021 Sniper - can you explain further about the bypass? Jerry - very correct, who knows what these old parts have been through? Quote Link to comment Share on other sites More sharing options...
keithb7 Posted October 9, 2021 Report Share Posted October 9, 2021 Some cylinder heads have a little bulge at the front of the head. There is a port in there for water pump by-pass routing. Other heads did not have this feature cast into the head. Quote Link to comment Share on other sites More sharing options...
Sniper Posted October 9, 2021 Report Share Posted October 9, 2021 1 hour ago, rrunnertexas said: Sniper - can you explain further about the bypass? Quote Link to comment Share on other sites More sharing options...
rrunnertexas Posted October 9, 2021 Author Report Share Posted October 9, 2021 Sniper - that is an interesting read for sure, full of information. When I get to the point of swapping the cylinder head I will need a new head gasket. I see many that have the "notch" in front for the bypass. The head on the car now and the one I'm looking at do not have the "notch". So, I'm assuming there is a different head gasket available for this application? Quote Link to comment Share on other sites More sharing options...
Sniper Posted October 9, 2021 Report Share Posted October 9, 2021 the head gaskets commonly available these days will work either way. As I understand it, the internal bypass HG will work on an external bypass head/block. I think, and someone correct me if I am song, that if you happen to find an external bypass style head gasket it will not work on an internal bypass head/block, it'll leak coolant. 1 Quote Link to comment Share on other sites More sharing options...
Los_Control Posted October 9, 2021 Report Share Posted October 9, 2021 Not sure if it helps, I can show a gasket and part # I bought from Napa a few years ago. Quote Link to comment Share on other sites More sharing options...
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