|
I'm not sure why the new TT V8s drink oil. Mine is about every 4500 miles like most you read about here. The ones drinking a quart every 1500 or so miles I think are a problem.
I don't believe there are any leaks or an intake issue. We would see blue smoke. Conventional wisdom would suggest that the turbos are responsible. The constant high pressure-feeds to the bearings most likely push oil past the bearings, especially on the hot side (turbine) when the engine and turbos are still "cold" before thermal expansion closes everything up. The oil is burnt off before we see it in the exhaust.
Remember we are running fairly thin oil at 5W-30. My E92 M3 used 10W-60 (which I thought was weird) and probably used about a quart every 15k or so. I think such a high viscosity oil probably wouldn't do a very good job lubricating the turbo bearings especially when cold.
There is no doubt valvetronic has its advantages. Like you suggest, it eliminates the pumping losses associated with "normal" throttling. This improves efficiency. Also, the theory goes, that under part throttle (engine warm) conditions, the lower valve lift improves combustion swirl resulting in improved emissions. I don't know where the "smoother" is coming from but perhaps that is also a result of the aforementioned.
From all the BMW material I've read, there were no other changes from N63 to N63Tu other than the addition of valvetronic and its associated hardware/software. I do believe BMW increased the boost slightly to gain the extra HP the Tu has, based on the engine's ability to meet emission and economy targets due to the valvetronic. Then again, automakers are always tweaking things here and there so we will never know for sure.
It does seem to me that the advantages of valetronic would be more pronounced in a normally aspirated engine. But I guess when BMW commits to a technology, they might as well go all the way. Hell, I don't even think there are anymore NA engines in BMW's portfolio.
|