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  Reply # 2092538 18-Sep-2018 13:29
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driller2000:

 

Coil:

 

driller2000:

 

Coil:

 

kryptonjohn:

 

It's amazing how much difference a 1.6km change in elevation makes over a 331km drive. On the weekend the drive from Auckland to the top of the Bruce Rd at Mt Ruapehu I averaged 7.8l/100km. On the drive back home I averaged 6.5l/100km! Similar traffic conditions each way - perhaps less traffic driving down meant higher average speed and worse economy though. 

 

 

 

 

 

 

Interestingly my car uses less gas at 135 than 100. Drops down to around 7L per 100Km at 135 and 8.5L per 100KM at 100. I think it is due to the car covering more ground for fuel burnt and thats in the sweetspot for that chassis. 

 

 

 

 

Umm - i guess it could appear this way from a cursory review of speed, mileage and fuel use from your gauges.

 

But measured properly - and even though my physics is pretty ropey nowadays - i don't think what you are claiming is physically possible - ie. from an energy perspective / 1st law if thermodynamics.

 

What with kinetic energy being a product of v2 - this greater speed requires more input energy output from your engine = more fuel needed....

 

 

 

 

 

 

 

 

 

 

 

 

I think at the same time you need to consider the new velocity and the new rate of ground covered also gear ratios and RPM. My gearbox throws my car into 5th around 90KPH then overdrive in 5th around 110 and that makes a noticeable difference.

I rely on my economy gauge on the dash so it could be wrong... 


 

 

 

 

sorry, but nope - none of what you said changes a fundamental law of physics.

 

 

 

ps: gearing will change engine rpm for a given velocity - but its throttle position that determines fuel use - and to go faster you will still need to burn more fuel

 

And - drag is also based on v2 as well - so your doubly borked the faster you go.

 

 

Not quite that simple due to the varying engine efficiency with RPM.




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  Reply # 2092545 18-Sep-2018 13:42
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driller2000:

 

Coil:

 

driller2000:

 

Coil:

 

kryptonjohn:

 

It's amazing how much difference a 1.6km change in elevation makes over a 331km drive. On the weekend the drive from Auckland to the top of the Bruce Rd at Mt Ruapehu I averaged 7.8l/100km. On the drive back home I averaged 6.5l/100km! Similar traffic conditions each way - perhaps less traffic driving down meant higher average speed and worse economy though. 

 

 

 

 

 

 

Interestingly my car uses less gas at 135 than 100. Drops down to around 7L per 100Km at 135 and 8.5L per 100KM at 100. I think it is due to the car covering more ground for fuel burnt and thats in the sweetspot for that chassis. 

 

 

 

 

Umm - i guess it could appear this way from a cursory review of speed, mileage and fuel use from your gauges.

 

But measured properly - and even though my physics is pretty ropey nowadays - i don't think what you are claiming is physically possible - ie. from an energy perspective / 1st law if thermodynamics.

 

What with kinetic energy being a product of v2 - this greater speed requires more input energy output from your engine = more fuel needed....

 

 

 

 

 

 

 

 

 

 

 

 

I think at the same time you need to consider the new velocity and the new rate of ground covered also gear ratios and RPM. My gearbox throws my car into 5th around 90KPH then overdrive in 5th around 110 and that makes a noticeable difference.

I rely on my economy gauge on the dash so it could be wrong... 


 

 

 

 

sorry, but nope - none of what you said changes a fundamental law of physics.

 

 

 

ps: gearing will change engine rpm for a given velocity - but its throttle position that determines fuel use - and to go faster you will still need to burn more fuel

 

And - drag is also based on v2 as well - so your doubly borked the faster you go.

 

 

 

 

Yeah I get all that so its either the gauge lying to me or there is something like how a boat reaches the plane at play here.
I have not claimed I have the answer to perpetual motion, I have merely said what I have observed.
Also with gearing my 6 cylinders at 100 are revving higher than they are at 110. Which is more individual fires per cylinder per minute which is more fuel. So where is the line between lower RPM but igniting more fuel per stroke or higher RPM igniting less? Also my engine makes different amounts of power at different RPM with a different efficiency depending on where it is? See what I mean...... It aint all black and white from what I can tell. 





 


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  Reply # 2092873 18-Sep-2018 21:14
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kryptonjohn:

 

Not quite that simple due to the varying engine efficiency with RPM.

 

 

Please explain how varying engine efficiency will overcome the First Law.

 

I will wait.

 

 


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  Reply # 2092878 18-Sep-2018 21:27
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Coil:

 

Also with gearing my 6 cylinders at 100 are revving higher than they are at 110. Which is more individual fires per cylinder per minute which is more fuel. So where is the line between lower RPM but igniting more fuel per stroke or higher RPM igniting less? Also my engine makes different amounts of power at different RPM with a different efficiency depending on where it is? See what I mean...... It aint all black and white from what I can tell. 

 

 

 

 

Surely if you sit at 100kmh with minimal throttle it will stay in it's highest gear. I wouldn't rely on the guage, my car has a real time usage as well, but it's useless, if I breath it shoots up, it's constantly changing (naturally). If anything my actual average usage is slightly conservative, it will say 8.1 when I've measured 8.0 (litres into the tank vs KMs driven).

 

But yeah if you drove at 70kmh everywhere you'd see astounding fuel economy. I know this because I get bored driving such big distances and was trying to get my car to average 5L/100km for a tank. Which involved driving quite slowly at times. Or conversely if you drive everywhere quickly, you'll see much worse. Like a racetrack!


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  Reply # 2092880 18-Sep-2018 21:32
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Can we maybe keep this thread to the actual fuel usage by people and start another one for discussion about it?


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  Reply # 2092887 18-Sep-2018 21:49
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Coil:

 

I bet I have the most expensive daily driver here.. 

 

 

Until very recently I was doing 185kms a day.. Averaging 17.8L/100kms

 

$250 a week just to go to work. Work out what it would cost in $NZD at NZ fuel prices...

 

 

 

4.4l V8 BMW X5 thru Adelaide Hills.

 

 

 

Now I'm getting 16.9L/100kms.

 

 

 

 


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  Reply # 2092888 18-Sep-2018 21:53
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mudguard:

 

Surely if you sit at 100kmh with minimal throttle it will stay in it's highest gear.

 

 

Mine won't stay in 6th until I'm doing 110.. Under that it prefers 5th (ZF 6 speed auto). Hate to think what it would do in sport mode.

 

Old 7 series was the same. Wouldn't even think of top gear unless you were doing over 105.


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  Reply # 2092889 18-Sep-2018 21:53
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blakamin:

 

Coil:

 

I bet I have the most expensive daily driver here.. 

 

 

Until very recently I was doing 185kms a day.. Averaging 17.8L/100kms

 

$250 a week just to go to work. Work out what it would cost in $NZD at NZ fuel prices...

 

 

 

4.4l V8 BMW X5 thru Adelaide Hills.

 

 

 

Now I'm getting 16.9L/100kms.

 

 

 

 

 

 

 

 

Yay someone with more $hitty gas mileage then me @ 13.9l/100km with my 6.0L V8 : )

 

 

 

PS: I hope you enjoy yours as much as I enjoy mine : )


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  Reply # 2092890 18-Sep-2018 21:54
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Jase2985:

 

Can we maybe keep this thread to the actual fuel usage by people and start another one for discussion about it?

 

 

 

 

Fair enuff :)


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  Reply # 2092892 18-Sep-2018 21:57
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driller2000:

 

blakamin:

 

Coil:

 

I bet I have the most expensive daily driver here.. 

 

 

Until very recently I was doing 185kms a day.. Averaging 17.8L/100kms

 

$250 a week just to go to work. Work out what it would cost in $NZD at NZ fuel prices...

 

 

 

4.4l V8 BMW X5 thru Adelaide Hills.

 

 

 

Now I'm getting 16.9L/100kms.

 

 

 

 

 

 

 

 

Yay someone with more $hitty gas mileage then me @ 13.9l/100km with my 6.0L V8 : )

 

 

 

PS: I hope you enjoy yours as much as I enjoy mine : )

 

 

 

 

Probably more, which is why I do it! :D

 

 

 

Mrs keeps saying I should sell it and drive my farm ute... I laugh and laugh and laugh and laugh and tell her she'll be out the door before my X5! 


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  Reply # 2092893 18-Sep-2018 22:00
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Our car - Bluebird Slyphy

 

Average = 8.2L

 

Best = 6.94L

 

Worst = 9.99L

 

(per 100km)

 

Actual real world results over 11,224km since bying it.

 

Tracking with - https://play.google.com/store/apps/details?id=mrigapps.andriod.fuelcons


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  Reply # 2092945 19-Sep-2018 08:04
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driller2000:

 

kryptonjohn:

 

Not quite that simple due to the varying engine efficiency with RPM.

 

 

Please explain how varying engine efficiency will overcome the First Law.

 

I will wait.

 

 

We are discussing whether a car can be more fuel efficient at a higher speed.  This quite obvious - it is just the actual speeds and the efficiency/speed curve that is debatable. Going to first principles of physics only gets you so far outside of a lab.

 

ICE engines have a peak efficiency range - for cars this could be around 3000rpm. To far above or below the efficiency will be terrible regardless of speed.. If you go too slow your engine will be labouring and run run inefficiently in a low gear. Your v2 becomes irrelevant below a certain speed where air resistance becomes low. 

 

Think about how efficient your car will be running at 100rpm in 1st gear at 1 kph and tell me how it will get more range than 80kph at 2000rpm in 8th gear? 

 

 


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  Reply # 2093058 19-Sep-2018 11:09
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I've a few toys ...

 

 

 

Suzuki DR-Z400SM  : 3.7L/100km

 

Smart ForTwo : 5.4L/100km

 

Suzuki Jimny : 7.4L/100km

 

Mitsubishi Delica D:5 : 12.3L/100km

 

 


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  Reply # 2093142 19-Sep-2018 13:52
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I have a spreadsheet recording my usage since purchasing my car and you can tell when winter ends and summer begins.

 

Last night I filled up 41.5 litres after doing 498km (roughly 8.3l per 100km) - we had a rather nice 10ish days (between fills) and I had the heater off which allows the iStop function to kick in at lights (when the brake is pressed hard enough). Compared to the previous fill where I had the heater on, I only managed 430ish km with approx 41.5 litres (worked out to be over 9.5l per 100km)


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  Reply # 2093358 19-Sep-2018 17:34
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Had to do a top up of fuel in Auckland last week as I forgot to fill up at home and the light came on .. heart sank when I saw the $2.64 a litre for 98!!  $20 got me only 7.5 litres, enough to get to Mangawhai and pay $2.32 a litre and fill it.

 

I thought the Auckland tax was only going to be a few extra cents ?!


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