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From: Daven Anderson
Remote Name: 220.127.116.11
Date: December 21, 2002
The medium-duty truck/Class A motorhome engine has an extra water passage in the block and heads, and uses RV12 spark plugs instead of the standard R12 type. This continued in the 1974-80 440 ci industrial engine (I have a 1974 motorhome 440). You can use regular heads on the these blocks,but the extra water passage in the block will be blocked. Everything works otherwise, assuming you match the head chambers to the pistons in the block (closed chamber '906' heads for closed chamber late 60's pistons, open chamber '452' heads for the '74-80 motorhome 440,etc.) The industrial 413 heads have exhaust valve seat inserts,which were put in for extra temperature tolerance BUT have the bonus in making those engines 'unleaded-fuel compatible' straight from the factory. By 1974 ALL of the B engines had exhaust valve seat inserts (to run unleaded fuel).