FYI comparison of crankshaft and flywheel weights N54 N55 S55

[Asbjorn]

I recently sat in the new BMW M4 DCT and was surprised at how free-revving the engine felt in neutral. The rpms would climb and fall much faster than I am used to in my N54 powered Z4 DCT.

I speculate some of it is down to throttle mapping in neutral. Because as most of us know, the N54 engine can change rpms very rapidly when demanded to do so by the DCT.

Rest must be down to differences in weight of the crankshafts and flywheels. So I decided to investigate what the differences actually are. Here are the results:



I was very surprised to find that the N54 *35is (ie both the Z and 3-series versions) uses a slightly different flywheel compared to the regular N54 *35i cars. I was also surprised that the M135i and M235i comes with upgraded crankshafts compared to the non-M performance versions and even the *40i cars which uses the N55 upper version.

I wonder if anyone here has installed light-weight flywheels on their Z4 DCT cars? As I understand it, reducing the flywheel weight may cause rattling, so it is primarily done on track-oriented cars. Reducing inertia may also be counter-productive on the drag strip...