A while back there was a thread “…..Chrysler,Dodge and Desoto early Hemi, what interchanges…..” and the discussion got around to whether Chrysler Poly (Spitfire) heads could be swapped onto a HEMI block.

I ended up in one of those right time and place deals and picked up a basket case 55 331 HEMI and 2 pairs of 55 301 Chrysler Poly heads (not to be confused with the Plymouth 301 heads). Poly info is a bit scarce but as far as I can tell the major difference between the 301 and 354 Ploy heads is intake valve size and I got a new set of 354 Poly valves on order.

Poly Parts

YJ3 by M Patterson, on Flickr


I’ve still got to get everything cleaned up and checked but if that goes well plans are to build the short block ……possibly taking it out to 354 if the sonic test goes well….. and setting it up for both the Poly and HEMI heads.

I’m mostly curious to see how the Poly heads stack up to the HEMI heads……it may do well, or it could run like a 273 with a burned valve, but there is only one way to find out.

At least the Tri-Power I pulled off the HEMI in the 57 Plymouth won’t go to waste as it will fit either combination.


T1 by M Patterson, on Flickr

1957 Plymouth (Hemi, Dual Quads, A833 4 Speed 9 1/4 w 4.10) Sold
1937 Dodge Pickup (Hemi, 6X2 intake, 46RH, Dana 60 w 4.56) Sold
1968 Plymouth Valiant 2dr sedan (354 HEMI, 46RH w/4.30 gears)