My H2AD
I am running an H2AD in my -4. I am an A/P I/A, and built this engine up from a run-out core. The H2 did get a bad rap back in the day, eventually creating an AD ( no connection to AD in the designation) requiring an oil additive to create better oil adhesion during times when engine was not being run. The other series of O-320's are not immune to cam spalling, its just that the H2 is a little more prone to it. The lifter body of an H2 is basically a Ford 302 drop in lifter, where as other variants are larger faced lifters installed from inside the case prior to assembly, giving slightly more contact surface. Several mods for the H2 include larger lifter bore/lifters, spray nozzles for the cam,ect. My engine has no significant mods, and the Aeroshell 100 Plus oil has the required additive already in it. The H2's have long performed well in the flight school C-172 environment, and many are still in service today. It is a 160HP engine and performs very well in my -4. I have over 200 hrs. on mine since the build, and I dont baby it by any means. Feel free to PM me if you have any additional questions about the unique features of the H2.