Torque and mpg

About the Granvia or about whatever....
Muckermatey
Posts: 30
Joined: 11 Aug 2015, 23:15

Torque and mpg

Postby Muckermatey » 20 Nov 2015, 20:22

Hi all.
Has anyone worked out what the optimum speed is, when cruising on a motorway, to achieve the maximum mpg? Obviously, you will use more fuel the faster you go, but will there be any noticeable difference between travelling at 60 mph, 65mph or 70 mph.
Also, if there are any mechanics on the forum – what is the relationship between ‘torque’ and ‘mpg’. If the engine is operating at the ‘revs’ that give maximum ‘torque’ does that also give maximum ‘mpg’, or is it not as simple as that. (If it was – you could just keep your eye on the revcounter instead of the speedometer)
Does anyone know at what revs maximum torque is produced?

Richard
Posts: 463
Joined: 28 Oct 2008, 16:48
Location: S.E. London

Re: Torque and mpg

Postby Richard » 21 Nov 2015, 12:11

The torque curve of an engine (torque plotted against rpm) will show at what point the engine is working most "efficiently". So to get the best fuel economy, that's the speed which should produce the best mpg. Unfortunately, it's not quite that simple! As the vehicle speed rises, aerodynamic and mechanical (eg tyre rolling) resistances rise so mpg should be best at the lowest speed possible, but this is compounded by the transmission ratios which will give the best mpg when the gearbox is in its lowest ratio (top gear). Confused yet? Now consider the Granvia's automatic gearbox and the fact that it locks its torque converter (the equivalent of a friction clutch in a manual gearbox) once the vehicle reaches a set speed, thus improving fuel economy by reducing slippage inside the torque converter. (You should feel a slight bump at around 56-58mph as the torque converter locks and unlocks.)

My personal opinion (and how I drive to get maximum fuel economy on motorways) is to aim to get the Granvia's speed to be just above the point where the torque converter has locked, i.e. just below 60mph. (It is immensely frustrating that Britain's motorways have so many roadworks and have a maximum speed of 55mph, just *below* the point at which the torque converter locks on my Granvia!)

According to the Toyota specifications for the 1KZ-TE diesel engine in the Granvia, the maximum torque should be produced at 2,000rpm for both the standard turbocharged and the intercooled turbocharged versions (289NM and 343NM respectively).

Muckermatey
Posts: 30
Joined: 11 Aug 2015, 23:15

Re: Torque and mpg

Postby Muckermatey » 21 Nov 2015, 13:03

Hi Richard. Thanks for the above info and your thoughts on the matter.

Recently, I have done quite a bit of motorway driving and, because my wife doesn’t like me ‘speeding’, I have taken to keeping behind (and doing the same speed as) the numerous lorries and wagons that keep to the inside lane. They are invariably travelling at 60 mph (which means that I am too).

I have looked at the revcounter, when moving at 60 mph and it shows slightly under 2000 revs when ‘on the flat’ and slightly over 2000 revs when on a medium incline (presumably, it has dropped down a gear).

I would, therefore, agree with your thoughts on the matter – that 60 mph is probably the optimum speed for getting most mpg, whilst still travelling at a speed that is neither too slow (to be an annoyance to other drivers) nor too fast as to ‘gobble up’ the fuel.

Cheers, Mike
Last edited by Muckermatey on 21 Nov 2015, 20:42, edited 1 time in total.

Richard
Posts: 463
Joined: 28 Oct 2008, 16:48
Location: S.E. London

Re: Torque and mpg

Postby Richard » 21 Nov 2015, 13:42

I have looked at the revcounter, when moving at 60 mph at it shows slightly under 2000 revs


That's interesting! On my '95 Q-spec 2wd Granvia, at 60mph on the speedometer, the revcounter will be showing a fraction under 3000rpm. And at 60mph I would pass lorry convoys limited to the pre-April 2015 speed limit of 50mph (I haven't done much motorway driving since April.), so I'm fairly confident that my speedometer is roughly correct. (And it was calibated against GPS a few years ago.) Is your experience of keeping pace with lorries at 60mph since the lorry limit went up in April? If so, it seems to show that your speedometer is also correct, so why should our revcounters be different? I think I'll have to work out the gear ratios and calculate the mph/1,000rpm in top-gear. This may take some time.....

EDIT: Please ignore the above comment - my memory was defective! It's 2000rpm on my Granvia too.

Richard

PS: If you *really* want to minimise fuel consumption, then slip-streaming a big slab-sided articulated lorry (supermarket distribution lorries are ideal) by getting so close that you can feel your vehicle suddenly being sucked-in, that's the solution (and why lorries travel in convoy). Provided that you have the nerves (and the recklessness) to do it! In my motorcycling days, the ideal was a horse trailer: narrow enough to keep an eye on traffic ahead; usually pulled by a vehicle powerful enough to keep a steady speed up inclines and since the driver would be mindful of his/her cargo (his/her horse!) invariably driven with care.

Muckermatey
Posts: 30
Joined: 11 Aug 2015, 23:15

Re: Torque and mpg

Postby Muckermatey » 21 Nov 2015, 21:21

Hi, Richard.

I’ve only had my Granvia for 4 months. Not sure what ‘spec’ it is – but it’s a 3.0 litre turbo diesel, 7 seats, electric curtains, 2 sunroofs (one manual, one electric), digital display for cab heater controls, and alloy wheels with 215/65 R15 tyres.

I’ve just done a run down a local ‘A’ Road to check out the revs at 60 mph – and I can confirm that the engine is doing (just under) 2,000 revs!

On the topic of ‘minimising fuel consumption’ I have got into the habit of engaging ‘Neutral’ whenever I am stopped in traffic, and at traffic lights, in the (possibly mistaken) belief that this will be less of a ‘drag’ on the fluid flywheel and therefore save fuel. Any thoughts on this?

I am not able to give a reliable mpg figure yet as I’ve only just started to record the amount of fuel I’m putting in and the number of miles I’m covering – but I suspect that, when used around town/mixed with journeys of up to 5 miles, I am getting about 25 mpg. I don’t yet know what I’m getting on long motorway journeys.

Mike

Richard
Posts: 463
Joined: 28 Oct 2008, 16:48
Location: S.E. London

Re: Torque and mpg

Postby Richard » 22 Nov 2015, 11:24

Not sure what ‘spec’ it is

First, make a note of the data stamped on the plate above the engine compartment (just below the windscreen wipers when you open the bonnet). Then go to a web-site such as www.toyodiy.com/parts/ and enter your "Frame Number" to identify the vehicle; the system will display the details for your individual Granvia from the model type to the month of manufacture.

Dropping into neutral when stationary is good practice along with applying the hand-brake so that you don't dazzle the driver behind with your brake lights. It can only help improve the fuel economy.

Richard

grandad
Posts: 36
Joined: 26 May 2015, 21:16

Re: Torque and mpg

Postby grandad » 23 Feb 2016, 07:34

Have used my Granvia mainly for 1200 km trips from the prairies at 3500 ft down to Seattle ( sea level) and drive at a speed between 100-110km
and get 25mpg. Have noticed better mpg when staying around 100km, but dont have the numbers. My lock-up appears to be around 80km.
In order to save on fuel, you should know the worst mpg is from a stop to get going. In order to slow down, I use the gears, usually the o/d is enough.
Also, I have 225x75x15 tires at 30lbs.
Have a few questions: the fuse for the dash cigarette lighter has blown, but can find it?? Also what is the ECT switch for that says Power and Normal?
Was told to change the oil at approx 4000km, which I think is quite low, normally I chsnge it at around 10.000 km. I may have the oil analysed?
When the ambient temp. is around 0 degrees C the engine is hard to get going with just the glowplugs. Like to know what your experience is ?
Normally I switch on the diesel heater for about 15 min. to one hour and brings the temps up to just below driving temps.

Muckermatey
Posts: 30
Joined: 11 Aug 2015, 23:15

Re: Torque and mpg

Postby Muckermatey » 24 Feb 2016, 14:56

Hi Grandad.

I had the same problem with the cigarette lighter not working. Some cigarette lighters do not have a 'normal' type fuse - instead they have a 'fuseable link' in the wiring at the bottom, underside, of the lighter unit. You will have to replace the lighter unit or repair the 'fuseable link'. The following link to a YOUTUBE VIDEO explains it all and shows you how to do it. I repaired mine following the video and now use it to attach satnavs and phones.

https://www.youtube.com/watch?v=f2SphvH4Kno

Regards,
Mike

daveveal
Posts: 225
Joined: 05 Sep 2009, 15:09
Location: New Forest, Hampshire

Re: Torque and mpg

Postby daveveal » 24 Feb 2016, 16:49

Thanks Mike, that's a useful find!

I wouldn't personally just remove the insulating washer though. I think it would be much safer to replace the fusible link, maybe with a piece of fuse wire (covered) or a blade fuse and holder if there is room.

Dave
R 613 PEL - 1998 2wd Diesel self-build camper. Pearl white over gold. New Forest, Hampshire

grandad
Posts: 36
Joined: 26 May 2015, 21:16

Re: Torque and mpg

Postby grandad » 24 Feb 2016, 17:50

Thank you Mike and Dave , will have a look at the video and will probably use a blade fuse.
The wiring to the cigaret lighter behind the driver seat is fairly small gauge and maybe only good for light duty ie GPS etc
Do you know what this ECT rocker switch south west of the steering wheel is for?
Thanks again.


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