A lot of people claim the term "nailhead" came from the valves being oriented in an upright position, but the straight 8 buick that was available prior, among other inline engines also had the valves pointing straight up and down, and none of them developed the nickname "nailhead." . the term was originally a derogatory phrase, coined by hot rodders, in reference to the tiny valves ( primarily the exhaust valves) of the 53 and 54 engines which were only 1.25." although the valves got larger through to 59, the name still stuck. Buick always hated the phrase and chose to never adopt it. preferring the phrase "fireball" through 56... and starting 59, the nailheads were called "the wildcat V8." for 57 and 58, they were just "buick V8s." a lot of mystery surrounded buick V8, as to why they were purposefully designed to be restrictive, and not breathe well at higher rpm.. the nailheads were designed around the dynaflow. the goal was to move a heavy luxury car quickly from stop light to stop light with a transmission that was always in high gear and didnt shift, with low end, low rpm power in mind. they produced more torque than any americanV8 for their time era... despite the very restrictive cylinder head design, they had no problem setting land speed records in the 50s, making them very far from a "boat anchor." Although not very efficient by todays standards, they make plenty of power, even in stock form with a good transmission to keep up with todays' traffic and burn rubber for a block. Easiest way to spot a nailhead from across the street is the notoriously vertically mounted valve covers and distributor in the rear. the 215 and 300 buick engines ARE NOT nailheads. you will notice the distributor is in the front on those, like later buicks, and even though the valve covers appear to be straight up and down on those, they are not. its an illusion in the way the valve covers are made to mimic the look of the nailhead, which buick was evidently very fond of. otherwise, theres no one single part thats interchangable between the 300 and the 215 with any of the nailhead family, consisting of the 264, 322, 364, 401, and 425.