Author Topic: MPG for those interested.  (Read 40626 times)

Downsizer

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Re: MPG for those interested.
« Reply #240 on: September 27, 2018, 05:48:46 PM »
Coincidentally, I have just filled up with 32 litres after 405 miles, computer reading 59.7 mpg, actual is 57.5.  Miles remaining shown as 80 with 3 bars showing.  I think figures based on one tankful are unreliable unless you are very diligent up about "brim to brim", which I am not!
« Last Edit: September 27, 2018, 10:00:07 PM by Downsizer »

nigelr

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Re: MPG for those interested.
« Reply #241 on: September 29, 2018, 09:15:03 AM »
Interesting! I guess it depends on the roads we all drive on and prevailing traffic conditions. I live on the busy A6 and most of my driving is city / suburban, with the odd long trip. My 2013 ES manual is getting around 50mpg - I use fuelly to calculate actual fill-up MPG but the trip computer in the car isn't far off. The real benefit of the Jazz to me is that I park on a busy street and it's easy to slot into small spaces, but is big inside.

Omits

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Re: MPG for those interested.
« Reply #242 on: October 30, 2018, 07:16:09 PM »
Any vehicle for cruising you need the engine to be at the max torque which is normally 56mph. Go above that and down it goes.

Skyrider

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Re: MPG for those interested.
« Reply #243 on: October 30, 2018, 08:13:24 PM »
Any vehicle for cruising you need the engine to be at the max torque which is normally 56mph. Go above that and down it goes.

That is 5,000 rpm for the 1.3 and 4,600 rpm for the 1.5. Not the best engine revs for economy or 56 mph cruising.
« Last Edit: October 30, 2018, 08:19:57 PM by Skyrider »

John Ratsey

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Re: MPG for those interested.
« Reply #244 on: October 30, 2018, 08:29:50 PM »
Any vehicle for cruising you need the engine to be at the max torque which is normally 56mph. Go above that and down it goes.

That is 5,000rpm for the 1.3 and 4,600rpm for the 1.5. Not the best engine revs for economy or 56mph cruising.
One only has to look at the way the CVT version behaves at 56 mpg being at less than 2,000 rpm unless going up a hill. Also, last year's Land's End to John o'Groats on one tank of fuel https://www.theaa.com/about-us/newsroom/fuel-economy-record-attempt was done at a sedate 40 mph which, I'm sure, someone had figured out to be the sweet spot for best mpg. Faster would significantly increase the drag losses. 

There's also the difference between best engine efficiency and best vehicle efficiency but if our cars were more efficient at >4,000rpm in 3rd gear then why bother providing higher gears (less noise?)? I suspect that the iVTEC system messes up traditional thinking about maximum torque = best efficiency. For example, having half the inlet valves closed at lower revs improves the fuel mixing which helps efficiency at the lower rev range.

andruec

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Re: MPG for those interested.
« Reply #245 on: October 31, 2018, 08:57:28 AM »
Any vehicle for cruising you need the engine to be at the max torque which is normally 56mph. Go above that and down it goes.

That is 5,000 rpm for the 1.3 and 4,600 rpm for the 1.5. Not the best engine revs for economy or 56 mph cruising.
Well no, I'm not even sure it's possible. I'm currently commuting along the M40 and I sit in lane one with the CC set at 58mph. That's about 1,800 rpm. That'll be efficient because it's going to be running in Atkinson mode.

andruec

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Re: MPG for those interested.
« Reply #246 on: October 31, 2018, 09:01:47 AM »
Any vehicle for cruising you need the engine to be at the max torque which is normally 56mph. Go above that and down it goes.

That is 5,000rpm for the 1.3 and 4,600rpm for the 1.5. Not the best engine revs for economy or 56mph cruising.
One only has to look at the way the CVT version behaves at 56 mpg being at less than 2,000 rpm unless going up a hill. Also, last year's Land's End to John o'Groats on one tank of fuel https://www.theaa.com/about-us/newsroom/fuel-economy-record-attempt was done at a sedate 40 mph which, I'm sure, someone had figured out to be the sweet spot for best mpg. Faster would significantly increase the drag losses. 

There's also the difference between best engine efficiency and best vehicle efficiency but if our cars were more efficient at >4,000rpm in 3rd gear then why bother providing higher gears (less noise?)? I suspect that the iVTEC system messes up traditional thinking about maximum torque = best efficiency. For example, having half the inlet valves closed at lower revs improves the fuel mixing which helps efficiency at the lower rev range.
Yup. There's 'best vehicle efficiency' and there's 'extracting the most energy from a given amount of fuel'. The two can be mutually exclusive.

Driving style can be the difference between getting 30% of the energy out of the fuel (most engine efficient) and consuming 10 litres or getting 10% out and consuming 5 litres (vehicle efficient).

Oh and I forgot to update on the Momentum fuel. Inconclusive in the end. Certainly not worth the extra cost.
« Last Edit: October 31, 2018, 09:04:17 AM by andruec »

Downsizer

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Re: MPG for those interested.
« Reply #247 on: October 31, 2018, 05:22:30 PM »
Any vehicle for cruising you need the engine to be at the max torque which is normally 56mph. Go above that and down it goes.
Peak torque is only needed for maximum acceleration.  The beauty of CVT is that it should control engine revs to give the required power with minimum fuel consumption.  56 mph cruising could be achieved at all sorts of rpm, but only one consumes minimum fuel.

peteo48

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Re: MPG for those interested.
« Reply #248 on: November 03, 2018, 11:48:53 AM »
8th fill up and my first sub 40 mpg figures. 39.2. Average speed only 16 mph so the cooler weather and many hours in traffic explain this one.

culzean

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Re: MPG for those interested.
« Reply #249 on: November 07, 2018, 07:18:54 PM »
https://www.aol.co.uk/2017/12/08/honda-jazz-sets-new-world-fuel-economy-record-of-95mpg/

According to this article the Honda Jazz used for record setting mpg from lands end to John o'groats on one tank ( 9 galls )  of fuel was a manual gearbox model.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

Pine

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Re: MPG for those interested.
« Reply #250 on: November 07, 2018, 07:55:09 PM »
8th fill up and my first sub 40 mpg figures. 39.2. Average speed only 16 mph so the cooler weather and many hours in traffic explain this one.

Peteo,
Was your 39.2mpg taken from the on board gauge or actual fuel put in calculated against actual mileage.

peteo48

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Re: MPG for those interested.
« Reply #251 on: November 08, 2018, 11:51:45 AM »
8th fill up and my first sub 40 mpg figures. 39.2. Average speed only 16 mph so the cooler weather and many hours in traffic explain this one.

Peteo,
Was your 39.2mpg taken from the on board gauge or actual fuel put in calculated against actual mileage.

Hi - no it was actual - brim to brim method which I record on Fuelly. If memory serves the computer was around 43 mpg.

Downsizer

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Re: MPG for those interested.
« Reply #252 on: November 08, 2018, 01:37:14 PM »
https://www.aol.co.uk/2017/12/08/honda-jazz-sets-new-world-fuel-economy-record-of-95mpg/

According to this article the Honda Jazz used for record setting mpg from lands end to John o'groats on one tank ( 9 galls )  of fuel was a manual gearbox model.
Yes - interesting.  Although the official consumption test figures show the cvt to be more economical, the John o'Groats run was no doubt under very different conditions, trying to maintain a constant speed with minimum braking and acceleration.  The official test involves frequent stops and starts.  I suppose with a manual, the driver could retain exact control of engine revs at all times, which would not be possible in a cvt.

Skyrider

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Re: MPG for those interested.
« Reply #253 on: November 08, 2018, 01:51:54 PM »
https://www.aol.co.uk/2017/12/08/honda-jazz-sets-new-world-fuel-economy-record-of-95mpg/

According to this article the Honda Jazz used for record setting mpg from lands end to John o'groats on one tank ( 9 galls )  of fuel was a manual gearbox model.
Yes - interesting.  Although the official consumption test figures show the cvt to be more economical, the John o'Groats run was no doubt under very different conditions, trying to maintain a constant speed with minimum braking and acceleration.  The official test involves frequent stops and starts.  I suppose with a manual, the driver could retain exact control of engine revs at all times, which would not be possible in a cvt.

Just shows that there is no comparison between extreme economy and real world driving.

John Ratsey

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Re: MPG for those interested.
« Reply #254 on: November 08, 2018, 08:20:28 PM »
Yes - interesting.  Although the official consumption test figures show the cvt to be more economical, the John o'Groats run was no doubt under very different conditions, trying to maintain a constant speed with minimum braking and acceleration.  The official test involves frequent stops and starts.  I suppose with a manual, the driver could retain exact control of engine revs at all times, which would not be possible in a cvt.
Also, the CVT has lower transmission efficiency than a normal gearbox (more than compensated in normal usage by the better drivetrain efficiency). I'm sure that research into the optimum speed and gear selection would have been carried out beforehand to give the confidence that the journey was feasible (it would have looked bad if they had run out of fuel at, say, Inverness). The vehicle itself had been borrowed from a dealer and hadn't been teaked. What's the engine speed in the manual 1.3 Mk 3 Jazz at 40 mph in top gear?  Well into the Atkinson cycle range.

John

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