|
That sounds like a recipe for getting travel sick !
|
|
|
its basically on modern fuel injected petrol engines they are
i) more efficient up to 2000 rpm
ii) more efficient with the pedal floored or totally off (due to the way the air/petrol mix is most efficient at full throttle, remember modern systems dont flood the cyclinder like old carbs etc would have)
so technique involves changing up at 2000 rpm rather than 2500 or 3000 which is more normal, drastic clutch technique etc can make this very economical apprarently
and forgetting the normal gentle touch "economy" techniques, and trying to use the throttle either full on or full off as much as possible
perhaps not totally practical all the time in real life driving, but useful to know anyways
|
|
|
|
I know someone who drives like that - I recently suffered the torment of a several hours being driven by him. Constantly on and off the accelerator. I, who am never travel sick, came very close to it. He also steers in the same way, so cornering is like going round the edge of a big threepenny bit. I never heard him mention economy, as far as I know he's always done it.
|
expect the makers quoted economy figures to go up as their drivers during the monitored tests start to adapt to using these techniques
should also help the CO2 figures
|
|
When I drive from Leeds to Devon I always set out with the goal of being as economical as possible, which all falls apart after about 200 miles when the signs for Exeter appear and I floor it from that point on. It probably doesn't help either that I use Haldon hill as the car's performance test, since I know with a run-up it can just do 85mph up it with the accelerator flat to the floor.
|
|
|
|
I remember reading many years ago about the Shell economy competition (where they have rocket shaped contraptions on bicycle wheels doing 2000MPG) and that's exactly the technique they used.
|
BP your recollection is correct! However, I did a 200+ mile trip up the A1 the other day and the computer showed 55mpg. Enroute I thought I had been zapped by a scamera so I drove home a little more gently and got over 60 mpg and journey only took me 15 minutes longer. In the real world gentle on the pedals and a lot of anticipation seems to do the trick!
|
You could modify the accelerator so that instead of being progressive, it just had two positions - on and off.
And what was that bit about drastic clutch use to accommodate this comfortable new driving style? Fantastic fuel economy but a worn out clutch?
|
SWMBO drives in this on-off way and treats corners like threepenny bits in spite of years of advice from me to try it smoothly instead. I've even tried pointing out that we get 10 per cent more mpg from the same car and the temperature gauge reads a bit lower too if we do it my way.
She won't be reading this, I hope...
I've done a lot of driving behind SU carburettors, where the required style for economical results was to 'feather' the throttle all the time - difficult to describe but means having it at just the right point for smooth forward progress without backing off. It worked with Webers and Dellortos too and Honda PGM-FI doesn't seem to object either.
|
|
The easiest way to save fuel is to minimise braking. By anticipating more and allowing the car to slow down naturally on a closed throttle (no use of fuel at all on a modern fuel-injected car) you decrease your consumption significantly. Every time you touch your brakes, just remember the heat generated = fuel wasted. It's an easy technique to use and makes for a relaxing drive. Just watch other drivers and see how many times they brake when approaching a bend when they don't have to.
|
>>You could modify the accelerator so that instead of being progressive, it just had two positions - on and off.
I had a moped like that!
|
Without seeing the articles, that makes a lot of sense. Engines work most efficiently on boost if its a turbo diesel or higher RPM's on petrol's depending on the engine. Of course at higher RPM's you use more fuel so to limit the fuel in bursts would provide the most efficient economy. Would be a horrid drive though.
Feel like being driven by a chav in a nova through heavy traffic.
|
|
Some sort of flywheel and CVT combo could use this technique properly though I guess?
|
|
Tried this in SWMBO's Gti. I am certain that it is more economical, but totally boring. If I wanted economy I would by something soulless and dire. A Gti doesn't howl properly at this rev ranges, gad it was doing 60 in sixth........
|
Surely just because an engine is delivering its power more efficiently, it doesn't follow that you are necessarily using thet power to some useful purpose on the road. You might accelerate very efficiently up to 60, and then throw it all away by having to brake hard.
Somewhere I read that the most efficient driving technique is to imagine that the brake pedal is a valve for ditching fuel out onto the road, like a faulty aeroplane dumping fuel before landing.
|
It's not new at all, it's as old the trees (well almost). The techniques are simply a correction to many peoples poor application of economy driving techniques.
Modern cars have good low rev torque characteristics so changing up a gear sooner coupled with better driver anticipation and less use of the brakes all contribute to saving fuel.
When observation tests have been made around 90% of drivers drive towards roundabouts at excessive speeds when they should have lifted off at least 100-200 yards sooner. A new economy system whereby the rear brake lights are briefly displayed whenever a driver completely lifts off the throttle is currently being considered to provide an early warning of when a vehicle is slowing down, although strickly speaking this shouldn't be needed but due to the majority of drivers driving too close to the vehicle in front their braking distance is reduced.
|
|
Does an engine running at 4000rpm use at least twice as much fuel as one running at 2000rpm?
|
Does an engine running at 4000rpm use at least twice as much fuel as one running at 2000rpm?
>>
No, given the same load it would only be different by the relative efficiency which within that range will not vary be a factor of 2.
|
MT, I agree on the braking - have just had a 25,000 service and the front pads are 20% worn, rears 5% according to the dealers measuring stick. This was unusual enough for them to comment on (they can normally rely on changing the front pads on the second service).
I like to make progress as well, but that's not the same as racing where you're either on one pedal or the other; lift off at 70mph as you pass the countdown markers for a roundabout, and you'll only need a touch of brakes to adjust the speed if you don't have to come to a halt. Same applies with entering a lower speed limit or approaching a bend.
The lift-off brake lights sound like a good idea - the anticipation bit sometimes results in the following driver tailgating into a bend; funny thing is, because you are unhurried and arrive at the right speed you can pick the right gear as you reach the bend, accelerate through and suddenly they've disappeared!
There is one short slip road exit where I brake heavily every day - I don't like slowing on the main dual carriageway, and getting from 70 -20 in about 50 yards cleans the rust off the discs ;-)
|
|
No hard technical stuff here then yet such as loss of engine efficiency due to partial throttle useage which results in a lower compression ratio which, in itself, results in the engine running less efficiently!
|
In various similar threads in the past, I've described engine performance maps - despite the silly units, this web page describes the situation reasonably well;
www.agen.ufl.edu/~tburks/Handouts/CH2_Performance%...f
The main thing to grapple with is figure 2.4. Operating near the centre of the BSFC "onion" is the way to get most power per unit fuel burnt.
The problem is that we all demand good acceleration performance, which means that our engines are vastly oversized for cruising, and we fail to cruise efficiently because there is too much available power. We then throttle back, moving away from the BSFC sweet spot. Among the factos contributing here is the throttling effect on petrols as described by buzbee, but there are a host of others too.
Number_Cruncher
|
>>which means that our engines are vastly oversized for cruising,
A few manufacturers have had a go with Variable Displacement engines (shutting down cylinders when power demand is low) where the engine has enough cylinders to make that viable.
This must help with the throttle effect and improve BSFC.
It doesn't seem to be very popular though but i'm not sure whether thats becuase of cost / complexity / reliability or becuase it doesn't yield much improvement
|
>>A few manufacturers have had a go with Variable Displacement engines
Yes, I think the problems are that you still may have the friction and pumping losses of these cylinders. Even if you do something clever with the valving, you still will have the friction to overcome.
Number_Cruncher
|
The easiest way to save fuel is to minimise braking. By anticipating more and allowing the car to slow down naturally on a closed throttle (no use of fuel at all on a modern fuel-injected car) you decrease your consumption significantly. Every time you touch your brakes just remember the heat generated = fuel wasted. It's an easy technique to use and makes for a relaxing drive. Just watch other drivers and see how many times they brake when approaching a bend when they don't have to.
Spot on. Exactly the kind of technique I try to employ (not always completely practical). If I can approach a roundabout, have enough time to look around, and reach it at just the right speed to enable going around, all without having to hit the breaks but still not holding people up, then I consider it a job well done.
Most of the problem is people driving around low-speed roads in too high a gear. lower gears are a good thing overall in these conditions. It's also just the kind of driving that stuffs turbos prematurely.
|
Most of the problem is people driving around low-speed roads in too high a gear. lower gears are a good thing overall in these conditions. It's also just the kind of driving that stuffs turbos prematurely.
?? Cobblers, surely?
|
?? Cobblers surely?
I don't think it is actually. Labouring a TDI does stuff the turbo anyway...
|
|
Labouring it, perhaps, but wafting along at 900rpm on a whisker of throttle, surely not.
|
Labouring it perhaps but wafting along at 900rpm on a whisker of throttle surely not.
The problem being when you try to accelerate, still from 900rpm. Then the labouring starts. Plus as I say, no engine breaking (indeed at 900rpm the engine will often be trying to go faster rather than slowing down) so more friction breaking so less stable car and a slightly higher possibility of having a crash -- very little better than coasting if you think about it.
|
?? Cobblers surely?
Well it's the reason given over in the Parker's forum by a Renault tech guy for premature failures on some dCi engines. From personal experience it's borne out -- I know a few people who have experienced turbo failure, and there is a clear relationship between drivers who drive around in low gear "for economy" and torbos playing up.
If you think about it it makes sense -- if you ride a bike slowly at higher gears, the pedals turn more slowly but you're sweating buckets trying to keep going. My general rule of thumb (for petrol cars, your results may vary as always) is <20mph, 2nd gear, <40mph, 3rd gear, <60mph 4th gear. Unfortunately there are a frightening number of people in my experience who drive around in 30 zones, at 35mph "because my car doesn't like 30", and often in 5th gear as soon as they hit 35. Madness. My dad's terrible for it, judder judder judder.
|
OK, pont taken, but it's a question of sensitivity.
Drove around some awful northern city with a tobacco salesman once, he drove like that and his car - a Vauxhall - sounded like it. Judder judder, straight into second at 2mph, then top at 10 mph - gave me the horrors but I didn't say a word.
|
I think people who go on these driving improvement courses at the bidding of a court are taught the 'Thirty in Third' rule. (It was briefly featured in The Archers, which does love its Issues, early this year, so it must be true!) With a bit of practice it makes town driving a far more relaxed experience than fourth, since 30 is just at the upper end of where most cars are happy in third - the hint that the car is starting to want the next gear is your gentle warning that you're straying over the limit, and of course you still have enough engine braking to drop back to a safe speed simply by lifting off.
Don't know if instructors are teaching this method. I got it from an ex-Police instructor on a defensive driving course in 1996, eight years after passing my test and shortly after I'd got my first 2-litre car and was trying to make it do 30 in fifth just because it could. As Jase said, our parents' generation (taught in the 1950s) tends to drive around in ridiculously high gears - and yet they perversely reach for the gear lever to slow them down when the brakes would do it far better.
|
|
Well tried it out over 200 miles this weekend, I managed according to (unscientific I know) trip computer data and gained 20% over mixed rural, little bit of town and ,otorway. Yes I saved diesel, yes my carbon footprint was probably smaller, but my it was boring. Back to normal tomorrow bi-turbos unleashed.....why else by a decent car eh ?
|
|
|
|
|
