Kickdown sometimes reduces average consumption?

[Silver-Aurion]

I love this Aurion. So much power! Going to the airport today and for the first time ever having a full car. I was driving and the car drove like I was the only person in the car!

Anyway, coming back I wanted to over take a car doing 80KM/h on the freeway and I found this as an opportunity to give the car a decent kick down since I haven't done it in a while and I hear doing this every now and then can be good for the engine to get the crap out!

Anyway, I kicked down the car till it revved its tits off :P and slowed back down. And this made the consumption go down by a .1.

And this isn't the first time. I've noticed that every time I do a hard to medium kick down the consumption will drop by a .1.

Whats going on here?

[DJKOR]

Remember that the average fuel consumption gauge is only an estimate. It's not exactly what you will be getting in the end.

What you are getting is probably a bit of an illusion. See, when you revved the engine up, you most likely would have increased speed. Then when you were slowing/coasting, the car had more momentum in it, thus it could continue to move forward under more of its own momentum rather than with engine assistance. Because the ECU calculates and updates its average consumption every 10 seconds based on readings from the No.1 injector in combination with the distance travelled, in this time where the car is moving under less engine load, it would calculate this as being more economical since you are covering the same distance as before but with less engine work.

But this is all relevant to the time of calculation. So the car may think you are being fuel economic because you are rolling forward with less engine work, but realistically, you had to rev it up before hand to obtain this momentum.

[Adamsy]

hey guys,

yeah i had noticed the same thing, had always thought to my self mm thats kind of funny good to know why that is the case though :)

Although i used to be a bit of grandpa around town my car barely ever got above 2000-2500rpm but lately ive increased that by 1000rpm and actually getting slightly better fuel consupmtion... why would this be? fuel burning better or what?

[Silver-Aurion]

Hmm, that is interesting. I thought that it would be reducing fuel consumption because when I do a kick down you are expelling the gasses in the engine and replenishing with new and when you expel that old gas the car decides to run better? Or something like that... lol.

[Silver-Aurion]

hey guys,

yeah i had noticed the same thing, had always thought to my self mm thats kind of funny good to know why that is the case though :)

Although i used to be a bit of grandpa around town my car barely ever got above 2000-2500rpm but lately ive increased that by 1000rpm and actually getting slightly better fuel consupmtion... why would this be? fuel burning better or what?

Exactly, the Aurion doesn't like to be driven around like a granny. I've noticed the more I baby it the more it likes to drink its milk.

[DJKOR]

Although i used to be a bit of grandpa around town my car barely ever got above 2000-2500rpm but lately ive increased that by 1000rpm and actually getting slightly better fuel consupmtion... why would this be? fuel burning better or what?

Hmm, that is interesting. I thought that it would be reducing fuel consumption because when I do a kick down you are expelling the gasses in the engine and replenishing with new and when you expel that old gas the car decides to run better? Or something like that... lol.

Believe it or not, an engine is most efficient up fairly high in the rev range (something in the order of 75-80% or it's maximum). Engines reduce in efficiency when they vary speed and run at lower RPM's.

This is why you have things like diesel locomotives that run the diesel engine at a constant RPM which in turn, powers a generator. The power from this generator is used to power electic motors that run the locomotive. Also the basic idea behind a CVT. Keep the engine speed the same, but vary the gear ratio to suit.

It just happens that for a given load characteristic, it would work out more fuel economic for a car to run at lower RPM's etc.

I'll use my mountain bike analogy again. Imagine pedalling along in the highest gear at a constant speed. Now if you increase your speed ever so slightly and then maintain that speed, you will notice that you are pedalling a little faster, but the effort required on each pedal feels less. Basically you have the same thing with the engine. The RPM may have increased, but the load on the engine would have gone down a little.

If you may not have noticed, engines tend to produce their maximum power (and for some like the Aurion; torque) higher up in the rev range. This means that when cruising at a lower RPM, depending on the load you may be wasting more power maintaining that lower RPM.

As for giving it a kick down an revving it up to the redline every not and again. This won't really clear anything out so to speak. It just adjusts the ECU shift patterns etc.

And as for fuel economy, when it comes to highway driving, higher RPM doesn't always translate to better fuel economy. The difference between driving continuously at 110km/h and between 85-95km/h is quite amazing. You can get around 1-1.5l/100km better fuel economy if you travel between 85-95km/h on long drives. Because at these speeds, it's not just the engine economy you have to think about, but wind resistance.

[VF-X]

Yea.. It's simple physics. Imagine your engine breaks down and you have to push your Aurion back home..(I know it's a stupid example) From stationary to slow, you'll have to push really hard, but once it's in motion u only need a bit of touch to maintain that speed, however, when u want to move it faster, you'll have to run + push harder..

I have no clue why the readings give an instant better fuel consumption, but the fact that if u kickdown ur car often, the readings will be higher. I've been experiencing that in my daily driving.

[DJKOR]

Yea.. It's simple physics. Imagine your engine breaks down and you have to push your Aurion back home..(I know it's a stupid example) From stationary to slow, you'll have to push really hard, but once it's in motion u only need a bit of touch to maintain that speed, however, when u want to move it faster, you'll have to run + push harder..

You're kind of on the right track, but not quite. It's not to do with the change in speed (velocity if you really want to be picky of my wording here), but rather the effort needed to maintain it at a faster vs. slower speed.

I have no clue why the readings give an instant better fuel consumption...

Read my first post at the top.

[Hiro]

Hmm, that is interesting. I thought that it would be reducing fuel consumption because when I do a kick down you are expelling the gasses in the engine and replenishing with new and when you expel that old gas the car decides to run better? Or something like that... lol.

Please tell me you're not serious....

A 3.5L V6 at 3000rpm pumps approximately 875 litres or air per second (very quick back-of-the-envelope calculations there, so there may be some errors). You don't get exhaust gas "hanging" around in the engine, so the whole idea of expelling "old" gas and replenishing it with "new" gas is quite hilarious. Yes, some of the exhaust gas from the previous revolution is retained in the cylinder (it is quite hard to expell 100% of it), but it is minute in comparison to the amount that gets drawn through each revolution, and gets mixed in with the fresh gas, burnt, and exhausted on the next cycle.

If you care for an analogy, imagine the engine is your stomach. You eat food (fuel and air, the intake stroke), it gets digested in your stomach (combustion), the stomach absorbs the energy into your system (power stroke), and then you expel the waste (exhaust stroke, use your imagination :P). Obviously you can't expel 100% of that waste in one go, so some of it will get mixed in with the next lot of digested food, and will mostly be expelled on the next cycle. You are constantly ingesting new fuel, and constantly expelling waste - the system is almost entirely flushed each and every cycle, so eating faster (kickdown) isn't going to magically improve the quality of the digestion and expel this great amount of "old" waste that was "hanging around".

[tiresmokindad]

I love this Aurion. So much power! Going to the airport today and for the first time ever having a full car. I was driving and the car drove like I was the only person in the car!

Anyway, coming back I wanted to over take a car doing 80KM/h on the freeway and I found this as an opportunity to give the car a decent kick down since I haven't done it in a while and I hear doing this every now and then can be good for the engine to get the crap out!

Anyway, I kicked down the car till it revved its tits off :P and slowed back down. And this made the consumption go down by a .1.

And this isn't the first time. I've noticed that every time I do a hard to medium kick down the consumption will drop by a .1.

Whats going on here?

Nice car. But I think the car is over use by having a hard kick down. I think you must do it softly.

[DJKOR]

I think dunlops has a good quality. Most of the people are using this type of rims and tyres. I will recommend you to use it.

Nice car. But I think the car is over use by having a hard kick down. I think you must do it softly.

Hey guys. Do the quoted posts above look like a spambot in the making? If so, I think it has failed by not including it's spam links.

[mr_grumble2010]

On the topic of reducing the 'indication' of average fuel economy.

My travels to work include 50km of up and down hills.

If I leave the transmission in 'D' and roll down these hills with no accelerator, I don't find that the average falls very much.

However, if I put the transmission into 'Sports',gear down and ride the transmission down the hill, I will always usually reduce the average ecconomy by 0.1 each time.

Now, correct me if I'm wrong, but in both cases arn't the injector pulses disabled, allowing no fuel to be injected into the inlet manifold.

So why do I see the substantial reduction in average fuel consumption when I gear down, down hills

Steve

[DJKOR]

...

So why do I see the substantial reduction in average fuel consumption when I gear down, down hills

I can't directly comment since I don't know exactly how the ECU is programmed to do it's calculation. All I have are my theories.

Yes the injectors should be off in both cases, but maybe things work a bit differently with the Aurion. It could be possible that when you are in drive, the transmission would probably be sitting in 6th and probably not easily going to downshift. Now maybe due to the gear ratio and the speed you are travelling at the time, the ignition/fuel injection isn't completely cut as the engine is being driving at a speed which it determines isn't enough to be sustained from the momentum of the car alone. As a result, it just keeps on running the engine as if it were idling.

Then when you downshift in S mode, you bring the revs up more and the ECU then shuts off ignition/fuel injection since the engine is being driven at a much higher RPM.

Just my idea.

[mr_grumble2010]

Probably the case.

I notice that in 'D', the speed picks up as though it's still driving and not completely in fuel cut-off mode, Even more so when cruise is set, it just seems to be happy to build up speed as opposed to relying on the transmission to limit down hill speed.

I just put it down to being my first auto (a smart one at that )

Steve

[tekkyy]

Then when you downshift in S mode, you bring the revs up more and the ECU then shuts off ignition/fuel injection since the engine is being driven at a much higher RPM.

I agree and was going to say the same thing.

Not sure if 6 gears is enough to be relevent but sometimes I wish I could tell it to maximize fuel economy.

That is, down shift just enough to cut off fuel without stalling but not agressive with the engine braking.

After 2 years it still feels weird when the car slows down downhill and eventually you have to accelerate so people don't tailgate you.