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Old 08-08-2010, 11:40 PM
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Originally Posted by dre1984
yes gen 4 heads can be used on gen 6 but gen 4 heads cannot be used on gen 5
First, it's MARK IV (or 4) not gen 4, and there are gaskets made specifically for using Mk. IV heads on a Gen 5 block. These are what you want (from a V/R press release, presumably prior to the Gen 6 engine release):

General Motors 7.4L Head Gasket

General Motors (GM) 7.4L (454 CID) engines use two types of engine blocks: the Mark IV and Mark V. The Mark IV is found on 7.4L engines in model years from 1965 to 1990, and the Mark V is found on 7.4L engines in model years from 1991 and newer.

Often, installers will attempt to adapt a Mark IV cylinder head for a Mark V block. This conversion can be made if attention is paid to the coolant circulation. Mark IV and Mark V have different coolant flows and were originally designed for different head gaskets. If the conversion is not performed correctly, the engine will overheat, causing premature engine wear and damage.

Victor Reinz has designed two Nitroseal® head gaskets to specifically allow for this conversion. The installation requires Victor Reinz part number 4918 be installed on the right cylinder bank to maintain proper coolant circulation, and part number 4923 to be installed on the left cylinder bank for the correct coolant flow.

Victor Reinz part numbers 4918 (right bank) and 4923 (left bank) are available for GM 7.4L (454 CID) engines.
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