Modifying the Pierce "PM-I" 5-port cylinder head for the MGB. The Pierce PM-I cylinder head is a popular, stock replacement type cylinder head for the MGB. Because it is made from aluminum rather than cast iron, it is less prone to cracking and lighter in weight than the factory head it replaces. To achieve better than stock performance however, the PM-I requires just as much effort and attention to detail as it's cast iron sibling would.
CFM flow numbers at 28"H20 for the above cylinder head.
Additional Notes: One concern we recently have had with these cylinder heads (stamped with identifier 081 T ) is the instance of the valve guides offset toward the front of the cylinder head. This can be seen in the above photo by the lack of concentricity of the spring shim to the guide (even though the spring shim is perfectly centered in the spring pocket). This is an obvious machining error and is present for all of the guides uniformly throughout the improperly machined heads. The manufacture has informed us that they have not received complaints (the error has not caused failures they are aware of) and they feel the offset is acceptable for the standard, stock replacement use they intend the cylinder head be used for. Those wishing to modify, or have modified their cylinder head should take note of this problem, as larger valves and/or increased valve lift will make the incorrect placement of these valve guides potentially very problematic. If you were hoping to use one of these heads on a smaller bore MGA, we would especially advise you to check valve to cylinder wall clearance carefully before proceeding. Home | Cylinder Heads | Articles ©2010 Sean Brown All rights reserved. |