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Head Interchange - early 331 Hemi to late 354 Spitfire poly block

From: Hank Dozier
Remote Name:
Date: November 22, 2002
Time: 07:42:19


Sorry for delay, but even I need to look at my books/notes sometimes on what sounds like a *trivial* question! The heads will phyically swap between the hemis and the polys. There are a couple of nuances that you need to be aware of, though. First, the early heads had one head dowel pin size. In 1955, when the block was redesigned and the cooling passages changed to bring water out the fron of the heads, a new head gasket was required. Since there were issues with the usage of the *WRONG* head gaskets between pre-and late block engines, in 1956 they changed the dowel pin size to make sure that the mechanics would know the difference. Your block has the SMALLER locating dowel pin holes. Your heads have the LARGER. This is the *best* combination I can come up with for your conversion. Since your heads have no water outlets in them, you need to use the 1954 4bbl manifold or similar aftermarket version. Or bore your heads for a water outlet for the t-stat. Since your heads are *early*, you need to get a set each of the pre-1955 and then 1955 and later head gaskets and check them block to heads for water passages. Use the one that fits best, and then alter either head or block for the matching dowel pins. You should be OK on pushrod clearance through the deck openings on this engine, but a trial assembly is still in order to set the initial pushrod lengths (I suggest adjustable, as you may have some deck/head/rocker stand stackup variance, and shimming rocker stands that head bolts go through is scary) Cams from low-deck 331/354s fit. Use the '55 and up variety. The old long-nose type is expensive and obsolete anyway.


Last changed: July 19, 2018