[condor]

rippergeo : It is such a lot of fun shutting the door on an over revving petrol :-)

Tell me about it !

watashi75 : Contrary to popular belief, lugging may not always give best fuel efficiency.

@Watashi, thanks for that. While the example is a little simplified, I hope people are getting the idea.

lower throttle + more power (lower gear) + better combustion >> higher throttle + less power (rem it is in a higher gear) + un-burnt fuel

[anupmathur]

Originally Posted by watashi75

Contrary to popular belief, lugging may not always give best fuel efficiency. Let us assume for simplicity that fuel consumed is approximately RPM times throttle width.

First example, for a car lugging uphill in 3rd gear at 1500 RPM at full throttle,

Amount of fuel consumed = 1500 * 1 = 1500 units

If it is possible to do the same in 2nd gear at 2250 RPM (Swift gear ratio) at half throttle,

Amount of fuel consumed = 2250 * 0.5 = 1125 units

Second example, if a car is moving in 5th gear at 3000 RPM at full throttle

Amount of fuel consumed = 3000 * 1 = 3000 units

If it is possible to maintain this speed in 4th gear at 3850 RPM with even 3/4 throttle,

Amount of fuel consumed = 3850 * 0.75 = 2887.5 units

In fact lugging will never give the best fuel efficiency, but it might give the best fuel economy!
I could not understand the examples you have posted. Further they seem to over simplify the whole case.
I cannot imagine being in 5th gear at 3000 rpm on hill roads!

I think what you mean is that there is a difference in fuel efficient operation of an engine and the fuel economy. I can run an engine at an inefficient point of operation but I might be saving fuel for a specific journey. The price I would be paying is in terms of the longer time I would take to complete the journey; and the fact that the engine would not be feeling very happy!

If we are looking for the best/complete utilization of fuel used, the engine should be run in the zone of bhp where it's specific fuel consumption is the lowest.

[esteem_lover]

I cannot lug my car, only a car with good low end torque (mostly diesels) can be lugged.

Whenever I try to lug my car, I am greeted with a band of classical musicians from my dashboard, totally out of sync that I would have to down shift immediately.

[anupmathur]

Originally Posted by esteem_lover

Whenever I try to lug my car, I am greeted with a band of classical musicians from my dashboard, totally out of sync that I would have to down shift immediately.

LOL, you are lucky enough to know what 'the band' is trying to tell you!
There are those who do not understand till the car stalls!!
That's when 'the band' from behind you starts! Honk honk honk...!!

[GTO]

Most common form of lugging : Being in too high a gear at too low a speed. Even other types of lugging / labouring (going up a steep hill in 5th, towing a heavy load in 6th etc. etc.) revolve around using a high gear, at a time when a lower ratio would be better suited & drop the rpm back in optimum range.

Nope, I love my cars too much to let the engine labour. Have seen too many people lug their engines in the interests of fuel economy. Truth is : the engine probably isn't at its most efficient when lugging.

P.S. : The only work I make my engine do is at the other end of the revv-band

[esteem_lover]

Originally Posted by anupmathur

That's when 'the band' from behind you starts! Honk honk honk...!!

As long as the band from the back does not play 'Thud Bang Thud Screech Thud', its fine.

[condor]

esteem_lover : I cannot lug my car, only a car with good low end torque (mostly diesels) can be lugged.

It only appear so - lugging will be seen differently in petrols, cant do a direct comparison.

anupmathur : That's when 'the band' from behind you starts! Honk honk honk...!!

Band Bhaja diya !

[quicksilver]

Originally Posted by condor

It only appear so - lugging will be seen differently in petrols, cant do a direct comparison.

You also have the issue of knocking in Petrol engines, making it hard to not notice. Unfortunately, it is the petrol cars that get lugged/laboured most, given the differential fuel price.

[watashi75]

Originally Posted by anupmathur

I cannot imagine being in 5th gear at 3000 rpm on hill roads!

The second example is on plain roads not on hill. It is just an example to highlight loads at high speeds, which in this case is the aerodynamic load. The first example is to highlight loads at low speeds.

Of course, there is no point in talking about lugging unless there is a load in the first place! Lugging is about being in a higher gear at a lower RPM when the power delivered by the engine is not optimal.

Originally Posted by anupmathur

I think what you mean is that there is a difference in fuel efficient operation of an engine and the fuel economy.

My understanding is that fuel efficiency leads to fuel economy.

Originally Posted by anupmathur

Further they seem to over simplify the whole case.

The example is simplified but it is not far from truth either. This is the torque graph for Swift taken from one of the threads here.



The power delivered by the engine at 1500 RPM is almost half the power delivered at 2500 RPM and the power delivered at 3000 RPM is nearly 3/4 of the power delivered at 4000 RPM. So the net result is that fuel consumed might actually be less if the engine is at a higher power band during load conditions.

Without load conditions of course lugging is more fuel efficient.

[Shan2nu]

Without load conditions of course lugging is more fuel efficient.

This will be true only if you're calculating FE wrt to time and not distance covered.

Like i have mentioned in my eg in a previous post.

A car doing 80kmph@2200rpm in 5th might be consuming only 3.6ltr an hr compared to the 4.3ltr/hr for 100kmph@2700rpm but when you consider the distance covered by the vehicle at those specific rpms, you realise that even though the engine is consuming less fuel at 2200rpm in an hr, it is also covering a smaller distance in that time frame.

So when you look at FE from a "kmpl" perspective, you can't rely only on engine rpm and forget about vehicle speed.

Shan2nu

[watashi75]

Originally Posted by watashi75

Without load conditions of course lugging is more fuel efficient.

Originally Posted by Shan2nu

This will be true only if you're calculating FE wrt to time and not distance covered.

I should have added that this is only for a particular speed. 1500 RPM in 3rd gear and 2250 RPM in 2nd gear both translate to the same speed for Swift.

[Shan2nu]

I should have added that this is only for a particular speed. 1500 RPM in 3rd gear and 2250 RPM in 2nd gear both translate to the same speed for Swift.

Yup, since the distance covered in an hour remains the same in both gears, the only deciding factor here would be the fuel consumed by the engine in an hour (ltr/hr), which would be lesser at 1500rpm in 3rd.

Shan2nu

[watashi75]

Originally Posted by Shan2nu

Yup, since the distance covered in an hour remains the same in both gears, the only deciding factor here would be the fuel consumed by the engine in an hour (ltr/hr), which would be lesser at 1500rpm in 3rd.

On the contrary, I am saying 1500 RPM is 3rd will consume more fuel. I hope you agree that fuel consumed is *not* same when you are at 1500 RPM and hardly pressing accelerator as compared to the scenario when you are at 1500 RPM and fully pressing the accelerator (full throttle). I would call the first situation as "cruising" and the second as "lugging".

[Shan2nu]

On the contrary, I am saying 1500 RPM is 3rd will consume more fuel. I hope you agree that fuel consumed is *not* same when you are at 1500 RPM and hardly pressing accelerator as compared to the scenario when you are at 1500 RPM and fully pressing the accelerator (full throttle). I would call the first situation as "cruising" and the second as "lugging".

I was refering to your statement below :

"Without load conditions of course lugging is more fuel efficient."

Without load, 1500 in 3rd would be more FE.

Shan2nu

[Spitfire]

Lugging what lugging? I drive a diesel