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Re: Just a couple thoughts

From: Hank Dozier
Date: March 05, 2002


Only problem with the poly-to-hemi conversion is the lack of good cylinder heads. Most available are the 241/270 variety. The "premium" 315 D-500 and the KD500/Truck 315 units are much rarer, and therefore command high prices. The 325 DeSoto S-27 and 57/58 Dodge 325 polys (plus the 315 truck polys) have actually pretty close valve sizes. D-500 is 1.87 intake, versus 1.84 for the poly. Exhaust is almost a wash at 1.54 versus 1.51. I think the idea of a tri-power poly is unique, and the difference in performance to acquire the hemi paraphenalia can be thrown into the poly by a good head job. You can stick almost 1.90 intakes and 1.60 exhausts into that head. Make sure to get narrow/thin exhaust valve seats. You can put thin stem (11/32") Stainless valve into them, good double valve springs (CompCams has some), and a good hydraulic grind cam. Udse similar lift/duration/lobe centers to a 340 6-pack, and it should fly. Remember, you got a 3.8" stroke to generate the low-end torque, and giving it the upper end breathing, it should really come into its own. Make sure the lifters are anti-pumpup style, and I would suggest adjustable pushrods to actually set the travel on the lifters, especially idf you deck heads or block. Compression ratio should be in the sane 9.5:1 region to use these new blends they have out West and in high-smog areas.


Last changed: July 19, 2018