People argue with me about it, but the simple fact is, the slant 6 was not designed as a hydraulic lifter engine. The lifters don't have pressurized oil. There's no oil passage through the lifter bores. They changed nothing when they went to hydraulic lifters. This means the hydraulic lifters are the last thing to get oil, so they don't really pump up too well. The hydraulic engines oil the lifters "backwards". Through the block, through the head, through the rocker shaft, through the rockers and finally they get oil from down the pushrods. It doesn't take a college education to imagine the pressure loss. It's just a terrible design as a hydraulic lifter engine.