That is the bee's knees for diesels but works like crap in gas engines. That's what the early Jaguar V-12 head was like, flat with no chamber and the chamber was in the piston. Part-throttle combustion was so bad and it had so little tolerance to mixture variance it couldn't pass emissions. They designed the H.E. head with a fast-burn chamber and it was far more efficient. They were able to run high compression ratios with lean mixtures and pump gas just like with a well-built wedge-head V-8 with modern chambers like we see all the time. But then there was a trade-off with slightly reduced flow since the valves were no longer completely unshrouded like in the non-H.E. head. As you can imagine the early heads are typically recommended for all-out performance but the H.E. is recommended for street or dual-purpose use.
...I'm somewhat of a closet Jaguar guy lol hope to someday own one. Same goes for old Buicks. And a lot of other stuff tbh
