.se domain is SWEDEN. There's a pretty simple explanation about all this. And that explanation is different countries use different measuring standards, and the numbers they yield, on the same identical engine, may look different but is in fact, the same. For example, the original spec for European S54 engine is rated in Kilowatts for power, and Newton Meters for torque. Standard metric measurements that us 'Merkins don't use. To convert it to imperial measuring units (Horse Power and #ft) is a simple process. The confusion comes from differences in international measuring standards and differences between a British yard and American yard (literally). Let's take the base European power rating on the S54 of 252 Kilowatts. 252 Kilowatts converts into 342.62 Metric Horse Power (PS), or the common 343HP that we often see quoted by European publications. The same 252 Kilowatts converts to 337.94 standard Horse Power as measured by DIN standards, the common "standard" measure in Europe, which is the 338 number often quoted by British magazines (because Standard measures like pounds, inches, and yards is what British "imperial" measuring units are). To complicate the matter more, U.S. measuring standards, SAE, differs from DIN measuring standards. 1 SAE HP = 1.0139 DIN HP. 337.94 DIN horsepower as quoted by European standards = 333.37 SAE HP, which is what's commonly referred to as the standard HP output here in the United States for the S54 output on E46 M3s. This is the HP as measured by BMW at the crank of an S54 engine capable of revving up to 8,000 RPM. Now, horse power as measured at the wheels is a lot different. A dyno machine usually takes a measurement and then a voodoo formula applied to the number to adjust for atmospheric conditions, parasitic driveline loss, final gear ration and gear ratio as tested. Dyno numbers from car to car, from dyno to dyno, of the same brand, can vary as much as 10%. The numbers quoted above from the Swedish company that makes dyno testing machines seems to read much higher than typical result, most of the dyno readings on the MZ4 S54 engine seems to fall between 280-290 rwhp, and the 335i N54 engine seems to fall between 260-270 rwhp. At least the dyno is off by a fairly consistent basis. Also keep in mind that production tolerances may account for up to 5% difference in actual engine output. I've once witnessed two nearly identical E46 330Ci produce a pretty dramatic difference on the same dyno ran back to back. Somebody correct my math above if it's wrong.