Hi Guys

Just wanted to know which average speed will give the maximum fuel consumption as yours experience ?

Thanks
Regards
sumith

flat out...

max fuel economy or minimum fuel consumption is maybe what you are after?

Hi PIGDOG

I mean the Maximum KMPL that you can run on which average speed ? and also would like to know vice versa also

You will obtain the maximum fuel economy in the highest gear (top gear) at the slowest speed for that gear. Which is about 50kph in a Datsun 1200 with 4-speed.

The low RPMs minimize pumping losses inside the engine, while the low overall speed minimizes aerodynamic losses.

Conventional petrol engines are pretty inefficient off WOT. For example, a modern car with fuel consumption read out on the dash will read the minimum consumption per kilometer at around 80kms/hr and this is for a fuel injected car that can lean off and hence reduce losses off WOT. If you could get rid of the throttle minimum speed is minimum consumption.

You could figure it out with a fuel flow meter, divide the readout by the speed and you've got your measure. For a car shaped like the datsun with a carb, I'd guess at around 60-80kms/hr depending on a lot of things. It also changes with wind, tail wind faster, head wind slower, yawed wind slower again.

One things certain is that fuel consumption grows exponentially after the minimum, more or less.

Helpful?

Hi Guys

Thanks for Info

My Datto Gave me above 17 KMPL last week towards a 120 KM Journey with about 40 KMs hill country area, there is a considerable improve in fuel consumption after i bushing throtal shaft in the carb,i had average of 50 kmph

Thanks
regards
sumith

The best fuel economy is achieved as the maximum vacuum level that you can achieve under the conditions at the time.

If you can hook up a vacuum gauge, even if only temporary, you can test drive over roads that you normally use & try different speeds to give you different readings for comparison.

If you can find a good flat road somewhere then try driving up to whatever speed that you want, shen slightly reduce the throttle.
If you are careful you can cut the throttle back & raise the vacuum level without affecting the road speed.

Gently does it & you will be surprised just how little throttle opening it takes to keep your Datsun rolling along at a reasonable speed.

probably worth remembering with modern cars is that they prioritise lowest part throttle _emissions_ over part throttle economy. TO this end the a/f ratios and timing they have at cruise could actually be improved apon, so relatively speaking, older engines (if well enough developed and sorted by the manufacturer) do a little better at part throttle than their newer rivals.

Mind you, modern engines are getting better and better, all I'm saying is that if they didn't have to meet part throttle NOx emissions targets (for example) they could run leaner a/f ratios and more part throttle timing and use less fuel than they currently do, for the most part (mind you, direct injection and other parameters are closing that gap)

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