Do I use less petrol at lower revs?

[threebikesmcginty]

Aren't there cars already that do this? I seem to remember reading about somesuch, and how unnerving the silence is, when you're driving along and the engine stops.

I used to have a mini that did that, fuggin' thing.

 

[donnydave]

I would say that it would depend on the engine to be honest, they're all different and tuned and set up in different ways, some are happy to rev to oblivion, some aren't.

aah you beat me to it, the petrol engine in one of my cars is more than happy with you changing up at 1500rpm, but then again it only revs to 5200 as its 40 years old!

 

[albion]

Obviously it is mainly a yes but touch that accelerator too hard and it becomes more a no.

 

[wait4me]

Could anyone tell me what the atmosphere of Mars is like?

Sometimes busy so you WORK; occasionally laid back then it's time to REST, and at all other times you can enjoy yourself and PLAY

 

[GrasB]

Keeping the revs very low may keep the fuel usage down but it's down right abusive on the engine. I've taken apart a 55'000 mile fiat 1.4 16v turbo engine which was driven at 1200-1800 rpm most of the time. God, that engine was a mess! I think every gap I measured was outside factory tolerances & it required serious work to get it nice & tight again. I left the owner with instructions to keep the engine between 1600 & 4000. Result? The little thing in stock tune was keeping up with cars that been remapped & were supposed to have up to 40bhp more.

IMO vehicle manufactures change indicators have the engines revving too low these days. In a Fiesta 1.0 EcoBoost I find that going up any incline requires the driver to change down a gear or two, it also makes it very to allow your speed to creep up. The irony of this is if I ignored the change lights, which meant it was indicating for me to change up virtually every time I looked at the instrument cluster, and drove like I would normally, revving the engine through to 5000rpm at times, the car reported a 0.5mpg reduction in fuel usage.

 

[gavintc]

Just get an automatic, you don't have to think about that sort of stuff then.

I rent a car through work every 2-3 weeks and make a similar journey. If I am provided an automatic car, my fuel costs are considerably higher than a 'normal' car. Typically, the fuel costs for increase from around £17 to about £20 when I come to fill it up before handing it back.

 

[Archie_tect]

Having started one pointless car-related thread that's spun completely out of whack, I thought I'd take a crack at a second, so...

I try to drive fuel-efficiently. I mean, I'm not obsessive or anything, but other things being equal I tend to try to avoid hard acceleration, coast rather than brake, and so on. I was musing idly, as I do, about whether it saves fuel to be in arguably too high a gear at any given speed, on account of lower revs must mean fewer explosions, which presumably means less fuel used. In a way, it feels counter-intuitive, in that you can feel the engine is 'having to work harder' - like trying to cycle up a hill in a higher gear. Do car engines have an optimum cadence? Or is my original idea correct, ie, one rev = a precise amount of fuel, therefore lower revs means less fuel?

Swee'pea, everything in the 3 pages above ^^^^ is your fault.

 

[swee'pea99]

Swee'pea, everything in the 3 pages above ^^^^ is your fault.

 

[gbb]

A subject close to my heart...
I run a 1.6 SRI 2010 Astra for whatever reason, ive always, for years, driven as reasonably economically as possible. I regularly get 50mpg, occasionally 54 mpg in the summer and 47mpg if I push along a bit. Reading forums, its hard tp achieve these figures on a standardish petrol car. I drive a mix of styles, I can pootle along if the mood takes me, but even a 1.6 has some oomph to push along if needed.
Coasting or in gear ? Depends on how long for. If theres traffic behind, in gear, accelerator off..you use no fuel. However, if like me going to work in no rush, no traffic, I coast up to junctions from some considerable distance, you are running at maybe 300mpg for several hundred metres. So 50 metres perhap at little or no consumption...or 200 / 300metres at 200/300 mpg. It may be undesirable for some, but theres no traffic and im in no rush.
Low gear, better consumption...no. I dont think the gear is always relevent to consumption, speed often is. If I get stuck behing someone doing 25mph..my consumption is terrible, whatever the gear. Increa se that speed to 30 or 35..its far far more economical. The engine is labouring, this differs car to car, depending on its power bands.

 

[Matthew_T]

With my car having a little engine, you have to balance economy with actually moving. I can get up a really steep hill in second at about 2000/3000 revs with no problem.

My car has a problem with the idle, it is very high (1500,1600 when it first starts but goes down to 1000 after a while). I have researched into it (most common problem is just a clean of the idle control valve). But I wanted to know if this high idle actually uses more fuel than if the idle was at 700 for example?

 

[Shut Up Legs]

I've tried varying the amount of petrol I use, but for some reason, whatever gear I'm in, the petrol consumption is the same .

 

[donnydave]

One would expect a faster idle to use more fuel than a slower idle, at idle. Emissions will probably be better though. Once you're moving it may not make mich difference, but I may be wrong. That fast idle does sound a bit high but not completely ridiculous if its cold and you've got heater on full blast etc. On one of our cars if you turn everything on when starting from stone frozen cold it will idle up at 1500 or so.
On the other end of the scale ive had my other car idling at 600rpm

 

[welsh dragon]

 

[ayceejay]

'member that annual contest run by Mobil (?) to see who could go the furthest on a gallon? First the petrol had to be measured and the gauges checked, you put in a rev counter if the car didn't have one etc. etc.and drove like you had nowhere in particular to go. I knew a guy who won it several years - talk about annual retentive - sheesh.

 

[Archie_tect]

I may never forgive swee'pea .....