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  #31  
Old 09-24-2014, 05:35 PM
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Originally Posted by bawareca View Post
So why the engine with a narrower powerband shifts less
Because of the higher torque available at a specific rpm. The driver isn't using all available torque at any given moment.
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  #32  
Old 09-24-2014, 05:36 PM
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Ah, I guess I never really thought about active computer management limiting torque the way it does and at the point that it does. That is pretty impressive. I guess what impresses me the most now is that there really isn't a measurable (seat-of-the-pants) improvement with valvetronic versus without.

In essence, they seem to have actually RESTRICTED the engine in order to improve driveability.
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  #33  
Old 09-24-2014, 05:42 PM
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Ah, I guess I never really thought about active computer management limiting torque the way it does and at the point that it does. That is pretty impressive. I guess what impresses me the most now is that there really isn't a measurable (seat-of-the-pants) improvement with valvetronic versus without.

In essence, they seem to have actually RESTRICTED the engine in order to improve driveability.
And now bring fuel efficiency into it. That's the real goal. Drivability is just a bonus.

The X5 35i rating is the lowest of four or so different ratings, IIRC, but is broader.
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  #34  
Old 09-24-2014, 05:46 PM
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And that is, indeed, the truth. Broad, flat torque curves with lots of "area under" not only improve driveability, but improve fuel mileage, due to the reduction in time spent with large amounts of throttle input.

Hence, this is probably why the traditional "diesel versus petrol versus turbocharged petrol" seems to favor diesel until technology catches up on the turbocharged petrol side of the house.

Interesting. Thanks for bringing a engineer's perspective into the discussion. I know a fair amount about things like this, but it was good to hear another side of the story, rather than gas purists screaming at diesel enthusiasts, and vice versa.
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  #35  
Old 09-25-2014, 07:11 AM
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Drove for the first time on an extended highway trip for 118 miles on a 2-lane highway through 9 small towns so had to slow down and accelerate often and got 31.7 MPG. Cruise set at 62 MPH outside of the towns. Sure is nice filling up much less often than with the M6 although diesel is still more expensive than the 93 octane premium.
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  #36  
Old 09-25-2014, 10:44 AM
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Because of the higher torque available at a specific rpm. The driver isn't using all available torque at any given moment.
That is true for all engines,gas and diesel.You mention to the the other guy that we have to look not at the engines alone,but with the tranny and diff,as a complete drivetrain.But you now compare both engines as a standalone units.You miss to point out that the shorter gears on the diesel completely make it up for the narrow powerband for the sake of less torque to the wheels.But really the biggest downside of the US diesel to the 3.5i is the 6 speed tranny.The diesel with it's narrow powerband is the one that needs more gears.
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  #37  
Old 09-25-2014, 01:09 PM
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That is true for all engines,gas and diesel.
Yes, it is. But given the higher torque ratings of the diesel, at a given rpm and load, the diesel has more surplus torque, ie more headroom. So it can be programmed to shift less. That won't make it faster, but it provides that sense of power that makes owners think they have more hp than they do.

BMW could install a transmission with more ratios, and has done on newer models, but I suspect there is a diminishing return there.
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  #38  
Old 09-25-2014, 01:43 PM
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Or CVT LOL
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  #39  
Old 09-25-2014, 03:39 PM
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Yes, it is. But given the higher torque ratings of the diesel, at a given rpm and load, the diesel has more surplus torque, ie more headroom. So it can be programmed to shift less. That won't make it faster, but it provides that sense of power that makes owners think they have more hp than they do.

BMW could install a transmission with more ratios, and has done on newer models, but I suspect there is a diminishing return there.
I am confident that the diesel will get 2-3 more MPG on a freeway with 8 gear tranny.At 75 mph it is cruising with 2100-2200 RPM which is way out of it's efficiency range.
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