culasse
la culasse 12H-2923 est une bonne culasse, "big valve", étrange sur ce moteur US. l’arbre à cames d’origine est un assez bon arbre à cames.
«Starting in 1972 and lasting until about 1974 and a half, casting number 12H-2923 was used, this being the only production "big valve" head. We have also seen this same head with casting number 12H-2709 or 12H-2708 in European guise (without the air injector ports). These heads had two major changes from the 2389, one being the new 1.625" inlet valves and the other being a newly revised "open style" combustion chamber. These heads were still equipped with 1.343" exhaust valves. The rocker pedestal oil feed hole is in-line with the bolt holes. The combustion chamber depth is roughly .375" and has a volume of around 38cc's. These heads do require exhaust valve cut-outs in the block and provide 8.0:1 compression with the deeper dished pistons used in the new, later style engines. Because of the larger valve sizes and shallower chamber, these heads are commonly sought after items for racing and high performance use. These heads were fitted with "Type B" valves and spring hardware, but only used single valve springs.»
le cut-outs en question est destiné à laisser passer la «grosse» soupape.
