[puneet_b]

Thanks for this thread. I'm usually a rev crazy driver but with my new swift I think I'll be changing my driving style to be a little more FE following your thread.

[vijaycool]

Perhaps this link will change our minds of less fuel consumption W.R.T light throttle.

Browser Warning

As you can see at light throttle fuel consumption is increased as compared to 50% and 100% throttle. I can conclude we can get more mileage by shifting in the pattern 1-3-5 and keep the throttle wide open to reduce fuel consumption. I am yet to try this method and my gave gives 8.5 kmpl in city traffic with 90% A/C

Regards,
Vijay

[AvonA7]

Originally Posted by vijaycool

Perhaps this link will change our minds of less fuel consumption W.R.T light throttle.

Browser Warning

As you can see at light throttle fuel consumption is increased as compared to 50% and 100% throttle. I can conclude we can get more mileage by shifting in the pattern 1-3-5 and keep the throttle wide open to reduce fuel consumption. I am yet to try this method and my gave gives 8.5 kmpl in city traffic with 90% A/C

Regards,
Vijay

The link is very informative. Thanks for sharing.

EDIT : Thought it would be appropriate to share in this thread, in my last tank full I got a FE of 14.74 km/l, following the suggestions mentioned in this link (I read it thrice and important point to be noted is, this is my first owned/driven car! ). Car - Polo 1.2L petrol, with 80% a/c in full city drive.

[vijaycool]

Originally Posted by AvonA7

The link is very informative. Thanks for sharing.

EDIT : Thought it would be appropriate to share in this thread, in my last tank full I got a FE of 14.74 km/l, following the suggestions mentioned in this link (I read it thrice and important point to be noted is, this is my first owned/driven car! ). Car - Polo 1.2L petrol, with 80% a/c in full city drive.

Wow thats a kind of mileage I would ever be happy with my GTX. Also you would notice with full throttle the speed is quite adequate in the city compared to the feather throttle. May I know the mileage prior to this experiment. I will suggest to work with 50~75% throttle beyond that the ecu ignores O2 sensor input which make the engine run rich.

Regards,
Vijay

[AvonA7]

13.5 avg, can say an increase of approx. 1.25, which is much more than my expectation. I think few other things also help, like maintaining proper tire pressure, take it slow for the initial 2-3 kms, generally I switch on the a/c after the initial 1-2kms, not to gain mileage , but read somewhere that dashboard etc inside the car release benzene which at times can cross 20 to 40 times the permissible (40mg / sq. ft) limit depending on the temperature (if parked outside so more the release of these toxic gases). And needless to say this is harmful to us.

Anyways, these links and the discussion (posts) give so much more info which at times is contrary to popular belief

[vina]

Originally Posted by AvonA7

13.5 avg, can say an increase of approx. 1.25, which is much more than my expectation. I think few other things also help, like maintaining proper tire pressure, take it slow for the initial 2-3 kms, generally I switch on the a/c after the initial 1-2kms, not to gain mileage , but read somewhere that dashboard etc inside the car release benzene which at times can cross 20 to 40 times the permissible (40mg / sq. ft) limit depending on the temperature (if parked outside so more the release of these toxic gases). And needless to say this is harmful to us.

Anyways, these links and the discussion (posts) give so much more info which at times is contrary to popular belief

I went through the link you had sent an didn't find any driving recommendations.

Can you throw some light on how to use this wonderful information?

[vijaycool]

Originally Posted by vina

I went through the link you had sent an didn't find any driving recommendations.

Can you throw some light on how to use this wonderful information?

The whole article talks about this

"For example, anything that allows you to keep the throttle open wider and the revs lower (like changing up to a tall gear and then holding it) will reduce fuel consumption because BSFC will be improved."

[vina]

Originally Posted by vijaycool

The whole article talks about this

"For example, anything that allows you to keep the throttle open wider and the revs lower (like changing up to a tall gear and then holding it) will reduce fuel consumption because BSFC will be improved."

thanks, but this is a recommendation that is well known already -> lower rpm = better FE (even if BFSC remains constant).


Also, I read the whole article multiple times, it works OK for old petrols, but it isn't clear whether the recommendations are valid for MPFI engines (with their closed loop controls and variable timing, some of the shortcomings are already gone) and since the whole article talks about engine breathing, the theory may not work at all with turbo diesels.


the recommendation above will of course work.

[vijaycool]

Originally Posted by vina

thanks, but this is a recommendation that is well known already -> lower rpm = better FE (even if BFSC remains constant).


Also, I read the whole article multiple times, it works OK for old petrols, but it isn't clear whether the recommendations are valid for MPFI engines (with their closed loop controls and variable timing, some of the shortcomings are already gone) and since the whole article talks about engine breathing, the theory may not work at all with turbo diesels.


the recommendation above will of course work.

No.. you are missing one thing. If you read carefully the BSFC chart is posted for the MPFI and Hybrid engines. Lower rpm will yield mileage no doubt. But people use their right foot feather light to gain mileage. The effect is < 25% of throttle opening and the BSFC increases by quite a margin. As you can see in the chart gm/Kw is significantly increased at lower throttle percentage. BSFC deals only WRT throttle opening not with rpm.
In simple terms if you need more mileage upshift early @ 1500rpm and "FLOOR" the throttle to 75% to get best mileage.

[vina]

Originally Posted by vijaycool

No.. you are missing one thing. If you read carefully the BSFC chart is posted for the MPFI and Hybrid engines. Lower rpm will yield mileage no doubt. But people use their right foot feather light to gain mileage. The effect is < 25% of throttle opening. As you can see in the chart gm/Kw is significantly increased at lower throttle percentage. BSFC deals only WRT throttle opening not with rpm.
In simple terms if you need more mileage upshift early and "FLOOR" the throttle to 75% to get best mileage

Got it.

However - you can not keep shifting higher, at some point for a given speed (usually constrained by factors on the road) the rpm goes so low, that you can stall the engine - also the article shows that very low rpm is also bad.

At such a low rpm, if the demand for power is not much (low drag, good road, lightly loaded car etc.) then you'll have to keep your foot feather light on the throttle, or the speed will increase which I'm assuming you don't want (because you may rear end somebody for example).


the one thing you post did was give a rational for accelerate-and-coast methods In these people speed up (and use more engine power) and then coast a little so speed comes down (and coasting in gear means fuel supply is cut by ECU) and then repeat the cycles.

Overall energy loss of the car in any journey due to external factors (drag, rolling resistance, etc.) will remain the same - so total energy requirement should remain the same, but if the article is correct they will be using fuel in more efficient bursts rather than less efficient constant burn at low power.

[vijaycool]

Flooring the accelerator wont increase in speed unless you are in torque curve. I used to shift 1-2-3-5 @ 2000 rpm. It directly puts you in 1500 rpm hence the engine wont be stressed. Instead a slight acceleration I just press 75% throttle for 3~4 sec when the speed picks up I drop the accelerator which is similar to Pulse and Glide technique. This can be done easily even in traffic and your can may not able to over take other cars but its not a dead horse. There is other added advantage with this technique. Due to the manifold pressure increase with higher throttle this will help the piston rings to push firmly against the wall, thus avoiding blowby.

Regards,
Vijay

[siddharth_menon]

Originally Posted by vijaycool

The whole article talks about this

"For example, anything that allows you to keep the throttle open wider and the revs lower (like changing up to a tall gear and then holding it) will reduce fuel consumption because BSFC will be improved."

I am following this for quite sometime .... 75% throttle lasts for few secs before you pick up speed :P, even with low speed high gears. But I guess this still saves me few drops.

Other thought, its all Drive by wire these days... wish ECU was smart to do this by itself. Stock ecu's are programed for all purpose driving so I know its difficult.

Btw I was planning to plug my laptop to OMBII port & monitor BSFC while driving. Just ordered a dongle, will take some time. Will keep you guys posted!

[vina]

Originally Posted by siddharth_menon

I am following this for quite sometime .... 75% throttle lasts for few secs before you pick up speed :P, even with low speed high gears. But I guess this still saves me few drops.

Other thought, its all Drive by wire these days... wish ECU was smart to do this by itself. Stock ecu's are programed for all purpose driving so I know its difficult.

Btw I was planning to plug my laptop to OMBII port & monitor BSFC while driving. Just ordered a dongle, will take some time. Will keep you guys posted!

ECU may already be doing this (as I wrote before).


On another thread some engine control guys mentioned something to the effect that ECU can figure out whether rpm is increasing/decreasing in less than one stroke of a single cylinder

If that is so, and car designers want, then using the TPS sensor input (it is pretty easy to figure out whether driver wants to maintain speed - he will not be moving his foot much, though road undulations etc. will move it a little) the ECU can figure out that "pulse and glide", as vijay calls it, may be the best way of going about it and then ECU can do it on its own by modulating fuel supply in engines (just don't inject fuel).

since ECU can do it at a granularity of per revolution (or a few revolutions) - it can do it so fast that the driver can never even notice this is going on.


Also if ECU is doing it already then trying to do this on your own will not only not buy you anything, it may actually hurt FE (though if for some reason ECU implementation can not be very good, then it'll improve the FE somewhat)

[souravc]

Interesting closing observation on how to achieve a fuel efficient drive

YouTube - ‪Prius More Enviromentally Damaging Than BMW M3‬‏

[AvonA7]

Originally Posted by vijaycool

No.. you are missing one thing. If you read carefully the BSFC chart is posted for the MPFI and Hybrid engines. Lower rpm will yield mileage no doubt. But people use their right foot feather light to gain mileage. The effect is < 25% of throttle opening and the BSFC increases by quite a margin. As you can see in the chart gm/Kw is significantly increased at lower throttle percentage. BSFC deals only WRT throttle opening not with rpm.
In simple terms if you need more mileage upshift early @ 1500rpm and "FLOOR" the throttle to 75% to get best mileage.

Thanks Vijay for summarizing.
Just sharing my thought on the bold part -

In my car (Polo 1.2 p) I don't upshift @1500 rpm, because if I do, this results in engine lugging (except 1st & 2nd gear). The car will pull but one can easily feel that its taking ages to gain speed. Moreover, engine lugging is not good for any car engine.

The increase in mileage I quoted in one of the above post is based on tank-full method (less than half empty tank) and I upshifted ~2000 - 2250 rpm.

No idea about other cars though.