The 1966 Chevelle SS 396 L78 is the performance specification that most Chevelle buyers didn't know existed. The standard SS 396 used the L34 in 360 horsepower form. The L78 raised compression to 11:1, added solid lifters, and was rated at 375 horsepower — honestly rated, where the L34's 360 was probably optimistic.

The L78 was a factory option that cost $158 over the base SS 396 price. It was not widely ordered — most buyers didn't want the maintenance demands of solid lifters or the rough idle that came with them. The cars that were ordered are rare and desirable.

Documentation: the L78 option code appears on the trim tag. The engine carries specific casting numbers. A claimed L78 without the trim tag code is a claim, not a fact.