Originally Posted by JK42
Sometimes it is, sometimes it's not. I've seen engine dynos of many BMW's, and they are not as over-powered as people usually think. The old 330Ci for example had 240hp instead of 231hp about 95% of the time, and about 305Nm instead of 300Nm on the engine. Seeing my own 130i on the dyno, it's engine had 272hp and 323Nm instead of the factory values of 265 hp and 315Nm, so the powertrain loss is still now very, very low.
This is because BMW has specifically stated that they have had huge success in decreasing the powertrain loss, and that RWD is the best technology to decrease it. BMW has added double-chain drives to the driveshaft on all N-series engines (such as N52B30) like they had on the S54B32 E46 M3 straight six, which is one of the biggest single areas of power loss of the whole transmission "chain". Also the driveshaft power distribution parts have been strenghtened with a totally new rear axle design beginning on the E90/E87.
It' interesting that you should bring up the E46 M3. Factory rated 333hp (here in the US). Most dyno around 275hp at the wheels. That's roughly 18% loss.
I'm not saying that the newer BMWs aren't more efficient or that they haven't made forward strides, but I can promise you that we pulled the engine out of your car and dynoed it. That you'd see more than 4% discrepancy between measured crank hp and measured whp using the same testing equipment.