Thoughts On Economy

[eco9rat]

What do you guys think if this theory, just passing time waitng for the car to be delivered... Its not simple and i hope i have explained it as clearly as i can. May have to ask a hypermiler on this one!

If you have a small engine (1.0 litre) and accelerate hard to get up to speed (call this X) or have a larger engine (1.33) and accelerate hard to get up to the same speed as X, the larger engine would burn more fuel while accelerating but get there fast but would the small engine use more or less fuel as would have to accelerate longer but burning less fuel per second.

I think 1.33 would use less as labouring of engine reduced so would be more fuel efficient on acceleration but less efficient when up to speed. Any thoughts.

Its not important but gets ya thinking doesnt it. :D

[reece]

Taking a Yaris as an example the extra urban fuel figures show the 1.33 is more economical than the 1.0 version.

As you have specifically mentioned the 1.33 engine which is in the iQ3, this blows the 1.0 out of the water!

Keep in mind that when at motorway speeds you will be in 6th gear using less fuel than the 1.0 which will be screaming. Also, whatever ‘extra’ fuel is used in acceleration is saved when you are sat in traffic with the engine off due to its Stop/Start

[macabeus]

If you where right than my Audi S6 should be more fuel efficient than my IQ.............................think again :o

[Cyker]

Well the start-stop would help, but there's just no getting over the fact that a bigger engine uses more fuel when running - It will have heavier moving mass which requires more energy to keep moving.

(And if you throw in the S6 which is what, a V8 and 4WD? All that extra crap adds loads of extra moving mass and friction which wastes even more power and thus more fuel!)

For fuel efficiency we want low-end torque; The higher the gear ratio you can run at a given speed the less fuel you will use - This is why diesels always beat petrol cars for fuel efficiency.

I'm sure the 1.33 has decent enough torque to comfortably run at 30mph in 4th, maybe even 5th in such a light car, but the 1.0 would struggle on the same gear ratio (Dunno if the gear ratios are different in the two).

As an aside, there're two schools of thought on the acceleration thhing; One says accelerating slowly and smoothly by setting the power at the level to get you up to the speed limit and waiting for the engine to pick up there at its own pace is best.

The other is to get to the speed limit as quickly as possible and then cruise.

Frankly, it doesn't make enough of a difference to matter; The first one probably works better when the engine is cold and the second when the engine is hot but if there is a difference it's too marginal for me to notice.

The absolute best technique for saving fuel is anticipating slow downs and stops so you can let the car slow itself down without braking.

[hertsnminds]

So many other factors not just engine size. Just for starters you will have the total weight of the car, the drag coefficient of the car shape, the rolling resistance of the tyres, how much of the power from the engine is lost through the transmission before it gets to turn the wheels etc etc etc

On the quick or slow accelerate you have to think does it use more fuel to fully open the throttle for 20 seconds or half open the throttle for 40 seconds. In theory that should use the same amount of fuel but will it get you to the same speed?