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      12-16-2011, 09:15 AM   #42

Drives: 2015 SO/CSAT F80 M3
Join Date: Jun 2006
Location: Canton, MI

iTrader: (1)

Originally Posted by bruce.augenstein@comcast. View Post
This is mostly incorrect, I think. In point of fact higher gearing (therefore lowering rpm at cruise) nets you better mileage, because there is less overall friction with reduced rpm, and more importantly, pumping losses are reduced. Pumping losses are associated with manifold vacuum (meaning when a cylinder is firing, power is lost because it must drive another piston down on the intake stroke against a vaccuum), and these losses increase when an engine is making more power at cruise, because you use less throttle to maintain a given speed, resulting in higher intake vacuum. When you use a taller gear, rpm is reduced, power is reduced, and you have to use more throttle to maintain a given speed. Therefore pumping losses are reduced.
I understand what you are saying above, Bruce. But I am convinced there must be more to the story. If you use a tall enough gear (ratio approaches 1:infinity), you could literally overpower the engine entirely. At this point, even if you floor it, you are just going to burn gas with no appreciable effect on the car's velocity. You wouldn't even be able to keep the car in motion. In the scenario, every single bit of fuel burnt is a waste. I realize this is an extreme example, but as you make the gear taller and taller, you approach this "dead-lock" situation. There simply must be a breaking point here. The formula simply cannot be that efficiency goes to infinity as gear ratio goes to infinity. It just doesn't make sense. There's got to be a drop off point, and I have got to believe it is gradual. You see what I mean?

They said the hell with mileage, and went for a strong and responsive engine at cruise.
I agree with Ateam on this one - it's not really strong or responsive at all. They really expect you to downshift to accelerate. But that aside, like I say, you still at least need the car to be able to keep itself at speed.
A gen-u-ine BMW eff-eight-zero with them tandem clutches in the transmission and that dad gum sun roof on the top-a da cawr.