As I'm taking a Chrysler 301 poly apart I was amazed at the port size and overall design. I'm making a 301 into a hemi with 55 hemi heads. The rocker assembly and push rods appear to be as new, I'm guessing this was the last gasp for this motor and the new rockers didn't help as the rest of the components are worn out. The new rockers made me consider for a moment rebuilding it with original heads, nope I'm building a hemi. Anyone know the value of this stuff or the interchangeability with other poly's?
I believe this was a polysphere conversion of the Chrysler hemi block used in Windsor and Saratoga to 1958. Parts won't fit any other block. The 301 was 1 year only. They should fit the Chrysler 301 331 or 354 block although, ports may be smaller than later versions.
That the 301 was a conversion block certainly seems possible, the push rod clearances look like a redesign to accommodate the poly head push rods, the valve reliefs on the pistons appear to be correct for the hemi head, I've heard people say that the 301 is not just an undersized 331, others have said the opposite.
I have disassembled several polys, including a '55 301. The valve reliefs look the same at a glance...but closer inspection will reveal one relief is 'clocked' a bit different. On a hemi piston the reliefs are directly 180* from each other. I 'think', but haven't proven, the poly pistons could be milled a little to correct the relief misalignment and the pistons used with a hemi head. I currently have a Dodge 325 poly and a set of 315/325 heads which will afford me the opportunity to test that notion. Ray
I always understood the 301 was a 331 Chrysler block with a 3/16 smaller bore. Next year's Windsor got the 331 block and the bigger jobs got bored out to 354. The last iteration was a 354 when the big engine was a 392. You can get confused by the welter of engines Chrysler used. In Canada they made a 303 version of the Plymouth block for Canadian made Dodges and Chryslers. This engine was borrowed by Detroit for the 1956 Plymouth Fury. In spite of the similar displacement the 301 and 303 are entirely different engines.
The 301 '55 Chr Poly is a low deck hemi based Poly vs the '57 301 Plymouth A Poly, a totally different engine. The 301 Chr Poly has a different casting number that the 331 hemi & one person said they had a sonic check done on his & it isn't an under bored 331.
After reading your comments I went out had a better look at the piston tops, the reliefs are indeed in 180 opposition the #7 piston had the marks STD-C I'm guessing this means standard Chrysler.
Hmmmm.......my 301 is long gone.....I'll have to see if I still have a set of Dodge 270 poly pistons laying around to reexamine. Maybe my memory is long gone too! The Dodge 325 is still together, so no immediate help there. Although the Dodge and Chtysler polys are two different size engines, sharing a common architecture, my observations to date, and long standing hemi lore, says the piston are slightly different. Ray
The 301 and 331 pistons are very different, the 331 are flat tops with larger reliefs, the 301 has a bit of a dome to it and the reliefs are smaller although in the right place, my plan is to take it and have it sonic checked and if there's enough there have it bored and get some new pistons, from that point its all familiar.
If you can bore it 3/16 you can use stock size 331 pistons which are cheaper than oversize. Hot rodders used to bore 331s to 354 for this reason.
I know this sounds impossible, but could I be wrong? and Ray is right? It did cross my mind to slap this thing together and run it, but all the parts are to expensive and hard to find to screw around. I went and took some steel wool to one of the piston tops for a good look and you can see the odd relief cuts, much shallower than the 331 Hemi, also take a look at the cut outs for the poly push rods, it looks like a hemi block adapted to poly like Rusty said.
With a sonic check it might go out to 331 std., but that would be a max overbore. I prefer a min overbore myself. Be cheaper to keep it a Poly, plus the "What is it?" factor. Notice on the pistons that they are offset, on a hemi they are opposite each other. Could be machined to clear hemi valves (probably) if you were converting to hemi, or you'd have to have custom pistons made for the conversion. You'd have to figure out the C/R if you machined the Poly pistons. The Mickey Mouse ears on the push rod holes aren't unusual.
It will be interesting to see how this all plays out. The sonic check will be the deciding factor. I have three sets of hemi heads and if I could find an alternative short block (331/354 polys) that would be the direction I would go. most of the available (rebuildable) hemi's I've seen, go for ridiculous prices, considering the cost to do just a simple rebuild. so I guess my next question is whats the ideal poly for this conversion? I would also add that after looking at the poly head engine, I can see why theres renewed interest in them
I am guilty of being a "hemi snob". The fact is, the polys breathe almost as well as the hemis, and almost is close enough to warrant their use. But would have to keep the hood closed, both for "their" benefit as well as my own! Ray
IMHO, the Hemi head on a 301 is pushing the limits of being waaay too much port/valve for 301 inches. NO, I do not recommend hogging out bores to get a cheaper piston or a couple of inches. This will sacrifice the value of having a thick cylinder wall in the first place. If you really need a Hemi then start with a 331-354. If you only 'want' a Hemi, then consider the 301 Spitfire. They are somewhat unique and can make plenty of grunt for their size. If you have weight restrictions then consider the 330-341 DeSoto or drop back to the 315-325 Dodge. All of the Spitfire innards are the same as the Hemi counterpart, and the intake manifold will swap so parts should not be an issue. If you need more than 8½:1 c/r then you will need a forged piston. All replacement cast pistons for the 301-331-354 are at oem c/r and when installed will not likely measure up to the claimed ratio so even if you bored the 301 out to use 331 slugs you are still left lacking...... .
The problem with using early heads will be the lack of front water ports for the water pump housing.....but, yes, the port size is a much better match. .
Couldn't you just smear a little JB Weld on the tops of the pistons to up the compression a little bit. (sorry I just couldn't resist) Converting a poly to a hemi is a neat trick just like bolting 426 hemi heads on a 440 block was a neat trick. I never really understood why other then to have a hemi. The poly head can be made to breath well enough to counter balance the difference in weight with the hemi heads but a man does what makes him happy I suppose. As far as parts swapping I would think that the rockers and shafts would fit the poly heads right up to the point that they changed to the later poly. That is just a guess on my part and @73RR lives in that realm so I would take his word before mine but I just can't imagine that they changed the rockers and shafts until they changed to the newer design.
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