RPM : Speed : Gear Position

[sethumurugan]

Re: RPM and Fuel efficiency

i have spark LPG LS model

00 - 10 First gear
10 - 20 Second Gear
20 - 30 Third Gear
30 - 40 Fourth Gear
Above 40 Fifth Gear

Till 4th gear I will make sure RPM is below 1500. After fifth gear, if i go less that 80-70KMPH it would be between 2000 to 2500. And after that depending upon speed it might go even upto 3200. I go above 60 only in highways.

But in city I get only 10 and highways i get 12

Am planing to meet the service guys for this assuming I can improve on FE and get additional 2 or 3KMPL.

 

[Lucas]

Re: RPM and Fuel efficiency

Hi everybody!! I have a spark petrol LT 2012.

I shift gears at around 2000 RPM.On highway I maintain between 70-80Kmph in 5th. I drive beyond 80kmph only for overtaking. My car gives consistently between 19-20 kmpl on highway without AC. With AC, it hovers between 16-18 kmpl. I've noticed that the sweet spot is around 2200 rpm.

i am neither heavy footed nor light footed driver. I just don't try to run the engine at very high or extremely low RPM. I genearlly don't look at the RPM meter now. Previously I used to look at it very often just to find the sweet spot and power band. Now I just feel the engine to shift gears.

Now an idea of my city driving conditions: it is like many other cities, 70% bumper to bumper traffic, bad roads, long waits in signals and so on. 5th gear can only be used during late night drives :-) In the above mentioned conditions I don't expect a consistent mileage figure. These are the FE figures using tankful to tanful method: in city the worst mileage I got, 9kmpl with 100%AC, when the car had less than 300km in odo. After crossing 2500km the best I got 16kmpl(intermittent AC).The Average hovers between 13-15 kmpl with intermittent AC.

One more thing. I have noticed that at rpm below 1500 and AC on, FE may drop. Above 1500 rpm car is very responsive and FE improves.

Whenever fuel indicator shows 2 bars, i fill up the tank. As the old Hero Honda add ( if I am not wrong) goes, "Fill it, shut it, forget it".

 

[350Z]

Note: Threads Merged.

Drive Safe,
350Z

 

[S Class]

The simplest thing to do is to hear to what car is saying. If you hear she is screaming, skip to higher gear, if she is coughing, shift to lower gear. Simple.
And don't follow the 0-20 or 40-60 philosophy. When going down on slope, you can use 3rd gear instead of 2nd, but while climbing you may require 2nd. The speed stuff is valid only on plain road, if there is upward/downward climb, you need to focus on sound only.
BTW, it is for this reason I prefer automatic (on eco/comfort mode).

 

[krish_go]

S class- So the gear method wrt to speed is not right and we should follow the RPM (the engine roar) ? Im trying get the best practice out of all the methods we use.

 

[sethumurugan]

Pls clarify me one thing which I have noticed today. I can drive in 4th or 5th gear in 700 to 800 RPM which is normal one when i start the engine and it is idle. Is this right? Will you get good FE in minimum RPM or More RPM

 

[Sam Dinkar]

@sethumurugan: I dont think there is any proper passenger car that could be ccomfortably driven in 4th or 5th gear at 700/800rpm. Even if there is such a car, you would be doing its engine a great disfavour by lugging it in that manner. Lugging the engine at very low rpms is as bad as revving it at very high rpms. Imagine trying to climb a slope with 100kg bag placed on your back while wearing shoes that weigh 10kgs each - thats exactly what your engine would undergo if you drive your car at 700-800rpm in top gear. Avoid it. Always drive your car in the optimum rpm range in all gears. You dont need to be a technical whiz to ascertain the optinum rpm range -just listen to your engine and exhaust, they will tell you when to change gear.

Practice !!

 

[sethumurugan]

@sethumurugan: I dont think there is any proper passenger car that could be ccomfortably driven in 4th or 5th gear at 700/800rpm. Even if there is such a car, you would be doing its engine a great disfavour by lugging it in that manner. Lugging the engine at very low rpms is as bad as revving it at very high rpms. Imagine trying to climb a slope with 100kg bag placed on your back while wearing shoes that weigh 10kgs each - thats exactly what your engine would undergo if you drive your car at 700-800rpm in top gear. Avoid it. Always drive your car in the optimum rpm range in all gears. You dont need to be a technical whiz to ascertain the optinum rpm range -just listen to your engine and exhaust, they will tell you when to change gear.

Practice !!

Thanks for Info.

It does n't mean that I do drive in 700/800 rpm regularly in 4th or 5th gear. Assume sometimes I will be driving in 30km speed and gear would be 4th and the RPM shows only 700/800. as per this, I assume you mean to say iam giving lot of load to engine but my sparky's engine does not seems to be like that.

I wanted to know will this be cause for my LOW FE.

I do not know will it have FE or not. As you say I do listen to the engine and I change the gear immediately.

But still confused with RPM and FE.

 

[Raja]

Thanks for Info.

It does n't mean that I do drive in 700/800 rpm regularly in 4th or 5th gear. Assume sometimes I will be driving in 30km speed and gear would be 4th and the RPM shows only 700/800. as per this, I assume you mean to say iam giving lot of load to engine but my sparky's engine does not seems to be like that.

I wanted to know will this be cause for my LOW FE.

I do not know will it have FE or not. As you say I do listen to the engine and I change the gear immediately.

But still confused with RPM and FE.

Spark has a good low end grunt . So even when you are in high gear and low speed it dosent knock but it dosent mean we must practice that analogy provided my Sam dinkar is the best one .
But iam unable to understand how you know the rpm of the car on given speed and gear because spark doesn't have a rpm meter atall . How you know the rpm iam really curious to know ?

 

[Sam Dinkar]

Let me explain all this in layman terms. Consider a human as an engine and the oxygen intake as fuel. If a human being is climbing a steep slope with 50kg load on his shoulders, he will breathe heavily (more fuel consumption). If you remove that 50 kgs load from his shoulders, he will climb the slope more easily and will breathe less heavily (low fuel consumption).

Very crudely speaking, a gearbox is used to alter the load on an engine depending on the road conditions (given the fact that the car is lugging 'x' kgs of load, i.e. its occupants). Depending on which gear you are in, the rpm of the engine varies to give you the necessary load lugging ability. Maximum power/torque are produced at varying rpm range in different engines.

Now consider your car in place of the human being moving up a slope. If you are driving in a a higher gear at a low rpm, the engine is straining to pull all that load and, like the human being with a 50 kg backpack who was breathing heavy, consuming more fuel than what it would be consuming if driven at the correct rpm (= removing the 50 kg backpack).

Some engines are more refined than others. I have driven the Spark and found it's 4-cylinder engine refined and silent with pretty good low end torque (pulling power at low rpms). Since the engine is refined, you don't feel it lugging at 700 rpm in fourth gear.

 

[sethumurugan]

Let me explain all this in layman terms. Consider a human as an engine and the oxygen intake as fuel. If a human being is climbing a steep slope with 50kg load on his shoulders, he will breath heavily (more fuel consumption). If you remove that 50 kgs load from hiis shoulders, he will climb the slope more easily and will breathe less heavily (low fuel consumption).

Very crudely speaking, a gearbox is used to alter the load on an engine depending on the road conditions (given the fact that the car is lugging 'x' kgs of load, i.e. its occupants). Depending on which gear you are in, the rpm of the engine varies to give you the necessary load lugging ability. Maximum power/torque are produced at varying rpm range in different engines.

Now consider your car in place of the human being moving up a slope. If you are driving in a a higher gear at a low rpm, the engine is straining to pull all that load and, like the human being with a 50 kg backpack who was breathing heavy, consuming more fuel than what it would be consuming if driven at the correct rpm (= removing the 50 kg backpack).

Thanks for the explanation.

Some engines are more refined than others. I have driven the Spark and found it's 4-cylinder engine refined and silent with pretty good low end torque (pulling power at low rpms). Since the engine is refined, you don't feel it lugging at 700 rpm in fourth gear.

That could be true. What ever RPM i told you was when I was going on slow speed. When I cross 40 the rpm would be some where 1500. when I am in 70 or 80 it would be somewhere in 2000 to 2500. if i cross 100 it might might go upto 3200 [ that is the max RPM I have seen in my car.]

Spark has a good low end grunt . So even when you are in high gear and low speed it dosent knock but it dosent mean we must practice that analogy provided my Sam dinkar is the best one .
But iam unable to understand how you know the rpm of the car on given speed and gear because spark doesn't have a rpm meter atall . How you know the rpm iam really curious to know ?

Mr. Raja, I have 2010 model in which there are lot of changes in the instrument panel and dashboard. In the model I have it has digital fuel gauge, temperature gauge, RPM, trip meter, clock and all warning lights in the instrumental panel itself. The front curvy portion where all the warning lights in the old model used to be, is just a storage [ Ppl say it can be used for sun glasses. since i don't use one I use that as wallet in my car. Keeping all money, cards etc]

Your Model Instrument Cluster



My Model Instrument Cluster



Apart from that, even the tail light also changed between yours and mine.
Your Model


My Model



From my model's Manual

 

[Raja]

@sam dinkar - thanx a million for a excellent explanation .

@ sethu- iam sorry never knew this changes happend that is why I was curious how you know the rpm .

 

[sethumurugan]

@ sethu- iam sorry never knew this changes happend that is why I was curious how you know the rpm .

That is okie Mr. Raja. I have edited the same post. I do not know whether you read it before my edit or after. Pls go thru if necessarily.

 

[Lucas]

@Sethumurugan, if you lug the engine, fuel consumption will increase. for your spark, try 2000 rpm to change gear if you want to go by RPM. Driving below 1400RPM and above 2600 RPM fuel consumption will increase. Try to stick between 2000-2400 RPM.

 

[Raja]

@Sethumurugan, if you lug the engine, fuel consumption will increase. for your spark, try 2000 rpm to change gear if you want to go by RPM. Driving below 1400RPM and above 2600 RPM fuel consumption will increase. Try to stick between 2000-2400 RPM.

Mr Lucas - I too have a spark which dosent have a digital meter so I was curious its all clear now