D'oh! Pretty much all of the nominations I could have thought of have been taken, and it's not like they were few in number: the BMW S54B32; the 911's flat-6, especially the turbocharged ones; the AMC 4.0L; the Toyota 2JZ; the Nissan RB26DETT, VQ-series, and VG-series; the VAG VR6; the Honda C30A/C32A...
Oh well, I have a couple more to add, namely, the
Nissan L-series straight-six, which powered the early Datsun Z-cars, and also this baby:
The BMW M88/S38
Based on the M49 six-cylinder of the infamous BMW 3.0CSL, the M88 was a driving force in establishing the inline-six legend that everyone associates BMW with. It displaced 3.5L, its two chain-driven cams actuated 4 valves per cylinder, and the Kugelfischer-Bosch mechanical fuel injection was paired with individual throttle bodies.
The first M88 engines, designated
M88/1, powered BMW's one and only mid-engined supercar, the M1, producing 277hp and 243lb.ft in the roadcar and an amazing
470bhp at 9000rpm in the first Group 4 racecars, by the use of upgraded camshafts, bigger valves, reshaped ports, forged pistons, throttle slides (instead of butterfly valves), and an upgraded exhaust.
Later, BMW would attempt to enter the M1 into Group 5 racing, developing
800-900hp from a twin-turbocharged and destroked (3.2L) version of the engine. This version of the engine was designated the
M88/2. However, the M88/2 was very short-lived, because the M1 project was cancelled soon after the engine's development was complete.
However, the M88 lived on in the E28 M5 and E24 M635CSi as the
M88/3, producing 286hp in Europe and 256hp in the emissions-choked u.s. This legendary engine is what really cemented the concept of the smooth yet powerful straight-six as the BMW engine of choice.
In the late '80s, BMW tweaked the M88/3 once again and renamed it to match the naming conventions of its other M engines. This engine was called the
S38, and powered the E34 M5 of the late '80s/early '90s. The S38 existed in two displacements -- the 3.6L S38B36 made 310hp, while the 3.8L S38B38 produced 338hp (the increase in displacement was in response to the Euro I emissions regulations in 1992).
Therefore, my primary nomination (since the S54B32 was taken already
) is the
BMW M88/S38.
After a quick Wiki, it would appear that the Air-Cooled and Water-Cooled flat-6 blocks were different. But from 993 back, they have been essentially the same block.
If my understanding of engine design is correct, why would an air-cooled engine have the water jackets and passages that a water-cooled engine requires?
Just pickin' on ya.
However it wasn't always a 4.0, there was a 199 (3.3L) and two versions of a 232 (3.8L) which evolved to a 258 (4.2L) and then along came fuel injection creating the 242 (4.0L) and eventually the 242 H.O.
.. I mean, nah what ever 
