Car fuel usage 1,6 litre petrol toyota

david4791

It's a known fact that driving at 55 mph at approx 2000 rpm is the most efficient driving form.

We had a debate in the office over fuel efficiency when the same car is driven at 30000 and 40000 rpms, does the fuel efficiency reduce by 50 or 30% or what percentage are we talking?

Only experts need reply to this please.

colm_mcm

It's not that simple....

At 55mph my s type is more efficient in 4th than in 5th

Avensis has a momentary fuel consumption meter, it should answer all your questions.


Also, 30,000 rpm will blow your engine up

david4791

That should have been 3000 and 4000 rpms

colm_mcm

Kinda guessed

Your 'known fact' is only a rough rule of thumb, you'd have to factor in

Gearing
Aerodynamics
Weight
Characteristics of the engine


The best way for your particular car is to try different gears, different speeds etc and watch the trip computer.

CiniO

david4791 wrote: »

It's a known fact that driving at 55 mph at approx 2000 rpm is the most efficient driving form.

I don't think it's known fact.
55mph is about 88km/h. My car is more economical at around 75-80km/h going at constant speed on 5th gear at abour 2200 - 2300rpm, provided it's even road. Up the hill it's more economical to reduce to 4th or 3rd and keep engine at higher rpm than overloading it on 5th at low rpm.

We had a debate in the office over fuel efficiency when the same car is driven at 30000 and 40000 rpms, does the fuel efficiency reduce by 50 or 30% or what percentage are we talking?

Only experts need reply to this please.

I don't think it's that much.
Going at 90km/h on 5th. If you reduce to third, your rpm will rise significently, but fuel consumption will rise only a small bit (I'm guessing maybe 10 - 15%).

CiniO

On a way home today I checked it empirically.
While my car is 2.0 litre petrol, I don't think it makes too much difference to 1.6

On 5th gear at 55MPH car does about 2500RPM and fuel consumption is about 6.1 l/100km
On 4th gear at 55MPH car does about 3200RPM and fuel consumption is about 6.9 l/100km
On 3rd gear at 55MPH car does about 4700RPM and fuel consumption is about 9.7 l/100km.
On 2nd gear at 55MPH car does about 6600RPM and fuel consumption is about 18 l/100km.

So by changing from 5th to 4th gear, RPM rose by 28% while fuel consumption rose by 13%.
By changing from 5th to 3rd gear, RPM rose by 88% while fuel consumption rose by 59%
By changing from 5th to 2nd gear, RPM rose by 164% while fuel consumption rose by 195%

Obviously my measures are not 100% accurate, as firstly onboards computer is not accurate, and road is not perfectly even. But they show general tendency, which is that fuel consumption rises way quicker than RPM.
So while you are not wasting too much fuel by driving on 4th instead of 5th, but you will waste big amount if driving on 3rd instead of 5th, and if you decide to keep the 2nd gear and very high RPM, you will waste extremely amount of fuel.

Hope this answers OP's question.

Pottler

CiniO wrote: »

On a way home today I checked it empirically.
While my car is 2.0 litre petrol, I don't think it makes too much difference to 1.6

On 5th gear at 55MPH car does about 2500RPM and fuel consumption is about 6.1 l/100km
On 4th gear at 55MPH car does about 3200RPM and fuel consumption is about 6.9 l/100km
On 3rd gear at 55MPH car does about 4700RPM and fuel consumption is about 9.7 l/100km.
On 2nd gear at 55MPH car does about 6600RPM and fuel consumption is about 18 l/100km.

So by changing from 5th to 4th gear, RPM rose by 28% while fuel consumption rose by 13%.
By changing from 5th to 3rd gear, RPM rose by 88% while fuel consumption rose by 59%
By changing from 5th to 2nd gear, RPM rose by 164% while fuel consumption rose by 195%

Obviously my measures are not 100% accurate, as firstly onboards computer is not accurate, and road is not perfectly even. But they show general tendency, which is that fuel consumption rises way quicker than RPM.
So while you are not wasting too much fuel by driving on 4th instead of 5th, but you will waste big amount if driving on 3rd instead of 5th, and if you decide to keep the 2nd gear and very high RPM, you will waste extremely amount of fuel.

Hope this answers OP's question.

I tried this too, but at first I couldn't work out what I was trying to record, then I couldn't find anything to write with in the car. When I did I managed to scrawl so badly that it was illegible and anyway, I'd already forgotten what I was trying to record. Then I spilt my coffee. Cinio, once again, I feel thicker than I did yesterday:D