When I put my GT40P in I spent some time trying to understand what I needed to do. So, here’s what I learned and believe is pretty accurate. First off is understanding what the cam is made out of. Ford factory cams are billet 5150 steel. They are fully machined even between the lobes. Ford used a steel distributor gear. Most aftermarket hydraulic roller cams are not billet 5150 steel. They are “SADI” or Selectively Austempered Ductile Iron. They are cast ductile iron that only the lobes are hardened. These cams you can use a regular cast iron distributor gear, the same as a flat tappet cam. I got this info from Howard’s Cams. Howard also told me all cam companies are buying their blank cores from the same suppliers.
This causes problems with distributor companies. I read a article by MSD said they as most aftermarket distributor companies use a Melonized gear. This is a hardened ductile iron gear. It’s the default material as it will work on flat tappet, SADI or billet Ford 5150 cams. I’m using a $29 MSD Melonized gear I bought at Autozone. I called MSD and verified it would work on a 5150 cam.
The other part of the equation is the gear must be properly located on the shaft. These MSD Melonized gears have only 1 roll pin hole drilled. You must drill a new hole through the distributor shaft 90* from the factory hole after you properly measured and located the new gear. MSD has a pdf on their web site how to do this.
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