Technical 301 poly with hemi heads

I've searched thru the threads and haven't found any clear concise info on this swap. does anyone here have knowledge of the swap? Heres what I've got: a 1955 chrysler 301 poly motor, complete, I have access to a pair of 1955 Chrysler 331 hemi heads, rocker arms, head bolts, a four barrel intake. My research concludes that it can and has been done, but no real info about it. Has anyone here done it?

 

I have done this same thing many times thye are a bolt on stup. no problem.

 

Thanks, olds guy. I guess I'll have to throw this stuff together and see what happens. any other info/pictures would be appreciated. I guess people will now start hoarding the polys.

 

I don't know if anyone has put the hemi heads on a 301 because of the small displacement.

If you want to, you can bore your block 3/16" and use stock 331 pistons. I don't know if you are planning a rebuild but it might be worth keeping in mind. Stock size pistons are cheaper than oversize.

 

That 301 used to be, possibly still is desirable to the salt flats crowd. It was about making a class. You'll need hemi push rods. The 301 pistons have valve clearance notches in the wrong locations and due to the difference of chamber volume the CR might make it to 6-1. Aftermarket pistons is the answer. Probably with the new pistons($), re balancing will be needed. The valves might possibly clear the cylinder walls.

 

It would be interesting to know if this could also be done with the other polys 56 331 and 57 354 if so I want one of those as well.

 

Yes the Poly 301, 331, 354 short blocks are all hemi based and all the same procedure. I bought several of the Polys many years ago when they were $20.00 each so that I would have spare short blocks in case a hemi got windowed or developed cracks.
WE55= 301
WE56=331
WE57=354
LE57= 354

 

Thanks 270dodge, now about compression ratio's 6-1?

 

Yea well, I think that the factory listed compression was about 7 to 1 on that 301. Those numbers were actually optimistic and proved to be high. Because of the bigger combustion chamber size and the lower piston to deck height you might be lucky to achieve 6 to 1 compression.

 

In this case, compression loss/gain is determined by the difference in chamber volume, Spitfire vs Hemi head.
The oem c/r for the 301 was 8:1.

The correct swap will have new 'Hemi' pistons to match the heads. Forgings will allow for any c/r you want and there is no need to hog out the bore.
IIRC, the Hemi valves need notches in the top of the cylinder...haven't done this for decades.
A properly rebuilt Spitfire with decent compression, cam, ignition, etc might surprise you as to what 301 inches can do.

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I have a pair of 301 blocks that were used in hemi conversions. Both have had the top of the bores notched for valve clearance. I have no history of what heads or valve sizes were used. Just an F.Y.I.

I did a quick sonic check on one. They are definitely NOT just a small bore 331 block.

 

That was the combo Gary Cagle used in his roadster . It was a giant killer. Maybe "fuel roadster" can give some details?

 

Windsor poly compression ratios:

55 - 8:1

56 - 8.5 : 1

57 - 9.25:1

58 - 10:1

Compression ratios on the same pistons with hemi heads will be lower because the combustion chamber is bigger. Also the exhaust valve notch is in the wrong place.

 

That's something I'd wondered about for some time now. What would be a max overbore on your 301?

 

Have you found the Hemi Tech Index yet?

 

I did look thru the hemi index, but nothing had the kind of info I'm getting now, thanks all. My plan (DANGER/WARNING) 301 Poly bored to 331 with new pistons, 354 cam 262, roller chain, 340 oil pump with adapter, 396 chev water pump, GM hei (sorry 73RR) headers. I've run this combination on other 331's and 354's with good results running in Mexico on Nova Pemex (83 octane) any suggestions are appreciated.

 

"73RR"s site has how to mod the rear cap for the melling M-50 392 hemi oil pump to avoid problems some have had with the altered 340 HV pump, & there a guy here who's supposed to be arainging for making int shafts to use unaltered 340 Hv pumps.

 

Out of one of my 331's destroyed in the High Park fire I was able to salvage a hexagonal oil pump drive for a 340 pump and the adapter, it was originally designed for a 392 and was to long and had to be cut down to fit the pump and cam gear in the 331 I made an identical set up for my 354 they both used cut down 360 pick up tubes.

 

iron or aluminum rods?

Its a bit tricky with aluminum rods and the relatively small (3-5/8) bore of the 301.

 

Stock iron rods, the next question is will the 301 block take the over bore? I've heard the 331 could take as much as 120 but I've never seen it.

 

I'd sonic check that 301 block first. They are a unique casting, NOT an underbored 331 casting.

331's can be different. Some are made from the 331 casting, but some (and not all) marine and industrial engines were made from the 354 casting but only bored to 3-13/16. Truck engines may be that way too, but I haven't seen enough of them to say for sure.

 

There is no advantage to giant overbores in the Hemi engines unless you think you need bragging rights. Whatever additional power the bigger bore might offer is overshadowed by using a forged piston and 10:1 c/r.
The big disadvantage of big bores is thin cylinder walls. A sonic check will help you sort this out.

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Worlds heaviest 301 v8 700 plus lbs . I wouldn't spend much doing it.

 

Sunbeam, well the plan was to do it based on what I have, trying to find a reasonable priced 331 hemi wasn't working, junk motors are now worth a bunch. to get a better understanding of why I would do this check out "Salt fever 2" on you tube, I went to B-ville a few years ago to spectate and a guy showed up with a full on movie camera set up and started filming. I sold this car a few years ago and now I want another(I know I shouldn't ) the stories go on for ten more pages........

 

If its for class I can understand But to many times I've used what I had instead of what I wanted and been unhappy in the end. There is a 354 poly in the for sale section for $350 but it's in Ohio.

 

Sunbeam, there's real wisdom in what you're saying, however the topic of the interchange has been around since I first started doing these motors and now I have a chance to do one. At some point I will likely bite the bullet and get exactly what I want, but for now this seemed real interesting to me, the more I research it the more interesting it gets.

 

The overbore really is (should) be dependent on the sonic check. I have a 331 that I only felt safe going .030. I have another 331 that is at 4 inch.

 

The sonic will be the main factor on the overbore.

 

I checked out a couple of parts sites, 73RR and TR Waters have some very nice stuff, TR I want those valve covers.