These are the correct type HLA to be used when shimming reduced base circle cams. The oil feed groove location machined in the HLA body will allow oil pressure to feed into the plunger assembly for proper operation when the HLA is raised up with shims. We have tested these to 8000rpm and higher in some applications all without any mechanical problems. These will also work with stock base circle cams. These are the best HLA's available for the 2.3!