MPG - Gear : Specific Vehicle Stats?

[EmailAddress]

The initial message was deleted from this topic on 24 September 2024 at 09:32

[Krikkit]

The problem with this is the immense amount of variability involved.

As a general first-approximation you'd look at a BSFC map for your particular engine, then work to get as close to the highest efficiency zone with gearing, but obtaining it isn't straight-forward.

[Krikkit]

EmailAddress said:

In theory, would there be a peak MPG RPM.

Regardless of gear or conditions.

Is 2000rpm in 3rd the same as 2000rpm in 6th as far as MPG goes?

My mind can't quite wrap around this exercise!

In isolation, yes. See below for a Brake Specific Fuel Consumption map - this is slightly limited because they're typically done at full throttle on a dyno, obviously if you're not at full throttle you can often have other losses which change it (e.g. on most petrol engines you have a throttle plate which will cause more pumping losses)



The region on this graph denoting 250g/kWh is the peak efficiency area.

In practice you can plot power levels on these, which are the curved lines running from left to right:

[NortonES2]

EmailAddress said:

Is 2000rpm in 3rd the same as 2000rpm in 6th as far as MPG goes?

No because if you are doing 2000rpm in 6th you will travel further than if you were doing 2000rpm in 3rd. Though using the same amount of fuel per rpm.

[Nicholas Turgeon]

Many years ago, I was involved in tests with an automated 5th gear.
The theory behind this was that the average driver ( who had probably been using a 4 speed box) made the wrong choice of gear between 4th and 5th about 40% of the time.
I designed a box in which the 4th gear had a freewheel and the 5th gear was engaged automatically with a wet clutch pack when conditions were appropriate ( as determined by the engine map). In tests, this measurably improved fuel consumption, but for various reasons was not pursued further.

[sideways man]

Autocar magazine used to do a fuel consumption report for every single road test.
From 30 up to a high speed , in 10mph increments.
Do they still? I haven’t bought the mag for a very long time.

[GT9]