Towing: 35i vs 35d

[bawareca]

Originally Posted by JCL

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What the diesel owners notice is that the vehicle doesn't need to shift as often. They describe that as feeling effortless. No argument. But it is still slower. And with the narrower power band of the diesel, and fewer gears in the transmission, it is a good thing it does have more flywheel torque.

Originally Posted by JCL

The N57 diesel is listed as having full torque available from 1750 to 3000 rpm, a 1250 rpm band. The N55 gasoline engine is listed as having full torque available from 1200 to 5000 rpm, a 3800 rpm band, ie 3 times as wide. While the N57 has greater peak torque, which would you describe as having more drivability/flexibility?

So why the engine with a narrower powerband shifts less

[JCL]

Originally Posted by bawareca

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.

[bawareca]

Originally Posted by JCL

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.

[JCL]

Originally Posted by bawareca

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.

[bawareca]

Originally Posted by JCL

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.