[Piwoslaw]

I was reading about dual mass flywheels today and one of the things I found was that it increases FE by 5% (Polish Wikipedia, which cites this article). Has anyone come across this info? Why would the savings be that big?

For those who don't know, here is a word about DMFs. Normally an engine has a simple, solid flywheel which helps keep the angular velocity of the crankshft constant. But there are still vibrations which need to be smoothed out since they can kill the transmission. This is usually done by some sort of spring setup at the clutch. A diesel engine has enough torque and vibrations at low rpm to still wreck havoc, so this is where the DMF comes in. It is actually two flywheels with a complicated mess of torque and vibration dampening machinery in between. This extends the life of the tranny and syncros, reduces noise and increases FE. The price you pay is pretty high: since it is so complicated, it needs replacing much more often than a normal flywheel or clutch and is much more expensive. About half of all European cars from the last few years have DMFs, and some owners prefer to replace their duals with a low-tech, solid flywheel when their time is up.