Thread: Fuel consumption

The biggest difference would be the wind resistance, especially if over 100 km/h

Originally Posted by Traveler

How do you work this out...
2 identical 93 Disco's 3.5l
both travelling from point A to B
one doing 2500rpm and arriving at B in 7 minutes
the other doing 2000 rpm and arriving in 10 minutes
car 1 has done 17500rpm using more fuel to maintain rpm but in less time
car 2 has done 20000rpm using less fuel to maintain rpm but taken longer time...
are their any other considerations?

Another consideration, how have you measured the actual fuel used? Your post is very vague.




More clarity needed or do I need more Clarette?

I'm sorry that is what i want to work out, which vehicle would use the most fuel.

ok I think I understand what your aiming at here.

assuming that everything is identical.. and you use the same vehicle to do the same distance under exactly the same circumstances other than one trip is done at a speed of 100 kph and the other is at 110 Kph then the vehicle driven at the slower speed will use the least amount of fuel.

Similarly...

If you did exactly the same thing but changed only the pressure applied to the throttle to get the vehicle up to the same speed then the vehicle that had the lighter throttle pressure applied would use the least amount of fuel.

Other than that theres a squillion other things that need to be taken into consideration to work out which will use the least amount of fuel.

starting at the ground and coming up

1. tyres, pressure, size, wear, tread pattern, constuction
2. driveline wear + lubrication
3. gear ratios, wear and lubrication
4. Transmission type
6. engine wear/lube/mods/condtion/servicing/operating temp
7. vehicle areodynamics
8. fuel quality
9. minute changes in ambient operating condiitions
10. additional loadings (driver weight extra fuel)

can you apply maths to this operation?

you can but you dont want to know about it the equations involved to cover everything are astronomical...

the best way is to do it on a dyno with a calibrated tank feeding the engine then give each engine a known quantity of fuel and run the experiments on what you want to do re speed and throttle. that way all other variables are elimnated

at speeds of less than 100 but more than 60 where is the 3.5 most fuel efficient. 1900rpm auto into 4th gear at 80kmh? {on flat surface}

Engine stress is also a big factor.

I dove our AUIII Falcon once, with a car trailer behind it, at 100kph.
In drive, (4th gear and convertor lock) it was sitting on approx 1,900rpm and the distance to empty readout was dropping quickly.

I moved the auto to 3rd, revs went up to approx 2,500rpm (cannot remember exact figures), the distance to empty stopped dropping and started to gain numbers.

Obviously the motor was under too much load, therefore lowering a gear reduced the fuel consumption.

With that in mind, the vehicle labouring the least at a given speed should use less fuel.

Ron