It's been mostly cleaning and inspecting parts. One of the Hemi heads is pretty badly pitted and going to take a fair amount of milling. Dave and I have been discussing options to save it if I can't find a replacement. The other head looks good and once it was cleaned up I got it CCed to get a base line of where we were at with that one.

Chamber volume came in between 100 and 102 CCs (from what I can find advertised volume is 103 CCs).


HH by M Patterson, on Flickr


I also got the first pair of Poly heads cleaned up. The intake side looks just like a first Gen Chrysler Hemi. The exhaust side ports are considerably smaller than the HEMI head but still decent size for a 354 CI engine.

P3 by M Patterson, on Flickr


P4 by M Patterson, on Flickr


The first surprise I found on the Poly heads was the weight. Almost every article about the Chrysler Poly heads says something to the effect that they were developed as a "cheaper and lighter head and valve train" alternative to the HEMI heads. On the cheaper and simpler side they succeeded pretty well. As far as weight, the bare HEMI head I weighed came in at 64 pounds........ the bare Poly 63 pounds


The bigger surprise was chamber volume. Common belief (including mine) is that Poly heads have a much smaller combustion chamber than the Hemi heads and that when doing a head swap to convert a Poly to a Hemi that a piston change is required to get the compression back up. A glance at the chambers would seem to confirm that.

P2 by M Patterson, on Flickr


Actually CCing the chambers tells a completely different story. On the first 2 heads that I checked chamber volume ranged between 102 to 104 CC (the 104 cc chamber was on the other head). Practically speaking going from Poly to Hemi or the other way around will not cause a compression change.


P1 by M Patterson, on Flickr


Once I get the other pair of heads cleaned and inspected we'll make the decision on what two to build. These 301 Poly heads and the 331 2 bbl heads use a 1.812 intake valves. I've already picked up a set of the 331 4bbl/354 intake valves that are 1.94s. All the Poly heads used a 1.5 exhaust valve and Dave and I are currently looking into a cheaper and larger alternative to the stock exhaust valve.


I've also been looking at the options for a roller cam.......any of the HEMI guys out running a street roller cam they would recommend?



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