This explains it
@FRANKIE
I believe it was the cost of getting thee s50 through emission rules in the US that resulted in a US only engine:
http://www.m3forum.net/m3forum/showthread.php?t=163292
What are the differences between the S50 and S52 engines?
The North American-spec powerplant, known as the S52, is based closely on the regular production M52 engine. Like that motor, the S52 is a six-cylinder with a cast iron block, aluminum head and four valves per cylinder, with two-stage VANOS variable valve timing on the intake strokes. Unique to the S52 is a bore of 86.4mm and stroke of 89.6mm for a total displacement of 3,152cc. The engine is rated at 240 hp (SAE) at 6,000rpm and 236 lb/ft of torque at 3,800 rpm.
In addition to the larger displacement, the S52 utilizes the following special M components:
-Ported and polished cylinder head
-Retuned VANOS variable valve timing for greater high-rpm power
-Heavy-duty valve springs
-More finely balanced camshafts
-Valve lifters, springs and spring seats with reduced mass
-Free-flowing intake and exhaust systems
The European-spec powerplant, known as the S50 B32, is a much more exotic unit. With a bore of 86.4mm and a stroke of 91mm, the S50 B32 has a total displacement of 3,201cc. Like the S52, it has an iron block and aluminum head with four valves per cylinder. However, the S50 B32 incorporates the following special features to allow it to produce an impressive 321 hp (DIN) at 7,400rpm and 258 lb/ft of torque at 3,250 rpm:
-Individual throttle plates for each cylinder
-Increased compression ratio to 11.3:1
-Advanced BMW/Siemens MSS50 engine management system able to compute 20 million instructions per second
-Double VANOS continuously variable valve timing on both intake and exhaust strokes
-Lightweight pistons
-Dual-mass flywheel
-Graphite-coated conrods
-Larger inlet valves
-Second oil pump
What are the differences between the S50 and S54 engines?
The S54 powerplant of the later M coupes is technically an evolution of the iron-block S50 B32 unit used in all European-spec M coupes built through June of 2000. Although the peak power and torque of the S54 (325 hp at 7,400 rpm and 261 lb/ft of torque at 4,900 rpm) are barely increased compared to the S50 B32 (321 hp at 7,400 rpm and 258 lb/ft of torque at 3,250 rpm), they share few major components and differ in many areas including:
-Increased cylinder bore to 87mm (from 86.1mm) for a new total displacement of 3,246cc (from 3,201cc)
-Modified camshafts
-High pressure Double VANOS continuously variable valve timing system with faster operation at high rpm
-Increased compression to 11.5:1 (from 11.3:1)
-More advanced BMW/Siemens MSS 54 engine management control
-Finger-type rocker arms for reduced reciprocating mass and friction
-One-piece aluminum head casting for lighter weight
-Scavenging oil pump to maintain pressure during heavy cornering
The S50 B32 unit can be identified by the "BMW M Power" inscription on its cam cover, while the S54 version contains only the "M" badge.
