[Doc Oc]

So several months ago I switched from 10/60 to 5/40. After the switch I was pleased with how rev happy it was, but the car seemed to have lost a little punch, which bothered me as I expected the opposite. I looked around here and discovered that although the majority felt that their car seemed quicker on 0w40, several people had the same feeling I did, that the car just didn't seem as stout after the change. Of course they were promptly told they were wrong, thinner oil equals more power, placebo effect, etc, but after doing some research on my next oil recently I came across this on the corvette forum which got me thinking about it again:

"Thinner oil will typically increase HP because of less viscous drag and reduced pumping losses, compared to thicker oils. That is why very serious Race efforts will generally use watery thin oils in their engines. But, an exception to this increase in HP would be in high rpm hydraulic lifter engines, where thinner oil can allow the lifters to bleed-off at higher rpm."

That's a small part of a very good write up that can be found here:

http://www.corvetteforum.com/forums/...0-vs-0w30.html

But that got me wondering if possibly this can happen with our high rpm hydraulic lifter s65 engine? Anyone have any knowledge on the subject? Could bmw have spec'd the 10/60 for this reason? I'm posting this because I'm trying to find a mechanical reason why my car seemed to lose something when I switched to the 5/40, which mechanically doesn't make a lot of sense. Any input welcome.