4. Chrysler 354 V8 Hemi
Chrysler introduced the 354 V8 engine in 1956 and marked it as a continuation of the Hemi engine family. It had a bigger displacement at 5.7-liters, better internals and intake system and more power. In standard form, it produced a lofty 280 HP. But when they equipped it with a bigger carburetor and different camshaft, it produced 355 HP. That was unheard of in 1956.
Historically, the 354 V8 with 355 HP in the Chrysler 300 B was the first American engine with one HP per cubic inch of displacement. They used the 354 Hemi in Chrysler and Imperial models, as well as a small amount of heavy-duty Dodge trucks at the time.