Thread: 2.7lt TDV6 fuel economy change

Originally Posted by DiscoWeb

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I have a bar and winch as well as a set of steel sliders but not RWC/ long rant tank, snorkel or awning.

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George

My long *rant* device sits inside the cabin Doesn't affect the wind drag...

Originally Posted by TerryO

On a slightly different topic I have noticed when towing our van that at around 80 kph the fuel consumption is dramatically better than towing at 110 kph.

How much better? By as much as 5 - 7 litres per hundred kilometres depending on the road surface and wind etc.

stands to reason, do some basic physics velocity / force calculations.

The vehicle is operating within a fluid, air and hence fluid dynanmics come into play, as in aircraft the Reynolds number becomes critical in determing the effect of the fluid on drag.i.e moving through that fluid.

Fd=1/2.pv^2.Cd.A that is just for the drag force, then use that in the power equation to obtain various velocities.

so air drag in this case increase with the square of velocity.

But . . .

Power required to overcome this drag or Fd is given by;

Pd=Fd.V=1/2.Pv^3.A.Cd

Hence the power required to push the vehicle and overcome the drag of the air fluid increases as the cube of the velocity.

As an example if the D3 cruises on a highway at 80 km/h it might require say only 7.5 kW to overcome air drag (Cd), but the D3 at 160 km/h in this example requires 60 kW of power.

Doubling speed the drag (force) quadruples as in the formula. Exerting four times the force over a fixed distance produces four times as much work.
(Sound familiar from high school physics? ).

At twice the speed the work (resulting in displacement over a fixed distance) gets done twice as fast. Now know that power is the rate of doing work, so four times the work done in half the time requires eight times the power. We have not factored in the rolling resistance in relation to the drag force in this either . . .

Bottom line you pay at the bowser for all your goodies and your right foot.

sorry guys geek in me having fun.

On a risk vs saving basis though...

Flowing at 100km/h means minimal interaction with large road users and minimizing of risk.

Driving at 80km/h to save a few $$$ could (and has) cost people a lot more!

Add in fatigue, driver frustration and impatience and you have all the makings of a disaster.


I often get on this soapbox, but have witnessed so many close calls, and a few that ended up fatal that this is just not a good scenario.

Originally Posted by Tombie

My long *rant* device sits inside the cabin Doesn't affect the wind drag...

I've kept the same one I had fitted to my first Disco. Still going strong, always been easy to fit to each new Disco and besides, you don't get much for them second hand.

Originally Posted by jon3950

I've kept the same one I had fitted to my first Disco. Still going strong, always been easy to fit to each new Disco and besides, you don't get much for them second hand.

Agreed, I have had the same one fitted to 3 Disco's as well as 2 Suzukis' 1 Pajero, 3 commodores and 2 Falcons. Still going strong, a bit worn around the edges but all functions still operable.

My only complaint is it seems to be getting noisier with age.

Originally Posted by jon3950

I've kept the same one I had fitted to my first Disco. Still going strong, always been easy to fit to each new Disco and besides, you don't get much for them second hand.

And i have the issue where it is hard to extract it from the drivers seat.....

I have to drive the ****box van all week,then comes the weekend and i am relegated to the passengers seat

With all my moods I'm around the 13l mark on average, drover the second D3 one week without a remap and what a change it makes for me remap or ecu upgrade is a necessity as it makes such a big difference