Quote from tristancliffe :

Wrong
But it'll also use less fuel per bang...

Hey Tristan, I don't understand how engines use fuel at all (I'm not joking, I don't even know which end of an engine you put the coal in). Is it as simple as highest revs = highest fuel consumption? And so is it more fuel efficient to drive in the highest gear you can?

It's a massively complex problem in the real world, as there are so many variables.

Labouring the engine (i.e. lots of throttle below about 2000rpm in an average petrol engine) or excessively revving the engine ( lots of throttle above about 6000rpm in an average petrol engine) won't do your fuel consumption much good at all.
With regards whether to use as high a gear as possible, it's unlikely that that would help until you have reached cruising speed. Whilst I've never seen (or calculated myself) any actual figures I subscribe to the view that high acceleration for a short amount of time tends to use less fuel (and is better for your engine) than less throttle for a longer period of time - i.e. get to 60mph quite quickly, using a reasonably amount of revs (~5000rpm) and then stick it in top and modulate your speed via small throttle inputs, as opposed to the grandad way of driving of taking 35 minutes to get to 60mph.

You use less fuel with lower revs (given the same throttle opening), and you use less fuel with less throttle (for a given engine speed) per unit of time, and hence distance. But an engine is theoretically most efficient at peak torque* and should therefore convert the most amount of fuel to motion at that RPM.

*the peak torque figure quoted by manufacturers is the 100% throttle peak torque. As you change the throttle, in response to load, gears etc) the actual RPM at which peak torque occurs would vary. Imagine putting a screw in the throttle so that you can only open it 50%, and then put it on the dyno to plot the torque curve - it would most likely have quite a different shape to the one plotted at 100% throttle.

Modern ECU's are getting better and better, especially when combined with throttle-by-wire systems, at controlling emissions, economy and power. Instead of controlling the throttle butterflies directly, the pedal then controls the ECU which decides what you want. Gradual depression of the pedal? You're probably after economy and low emissions, so it can play with the throttle and fuelling to give you that at the expense of power. Snapping the throttle open? You probably want to accelerate sharpish without worrying about economy (but it'll probably always try to minimise emissions on road car applications)....

Such a vast topic - which is why there isn't or hasn't been a single answer about what is 'best'. Especially as cars are changing quickly as petrol engine technology massively increases (you bought a Diesel? Poor you, they're so 1990s), so any 'best' answer would be out of date by the time you read it.

My advice would be to do what you THINK is best. For me that's accelerating quickly to my cruising speed using quite a few revs and then holding speed in the highest gear that doesn't labour the engine. For some it's acclerating slowly, changing gear at 2000rpm. Hell, my ex-girlfriend Dad was convinced by a so called "Advanced Driving Instructor" that skipping 3rd gear would massively improve his economy, so now he does. It's hasn't helped, it's increased his journey times, economy hasn't improved, and he holds up tractors. But he was told it was best, and no amount of discussion will convince him otherwise.

Generally you put the coal in at the back though.

Quote from tristancliffe :

(...) (you bought a Diesel? Poor you, they're so 1990s) (...)

Lol, typical petrolhead comment Diesel still is a far more effective fuel than petrol, no matter how you look at it. You may not like 'em, but that's entirely down to personal preference.

Well, they're not exactly good for performance, they're not exactly good for the environment, and they cost more to own and run in the long term (generally). They became very popular in the late 90s and early 00s, but petrol engines have been improving at a rate that will ensure diesels won't be a popular choice for most cars for much longer.

Quote from tristancliffe :

Well, they're not exactly good for performance, they're not exactly good for the environment, and they cost more to own and run in the long term (generally). They became very popular in the late 90s and early 00s, but petrol engines have been improving at a rate that will ensure diesels won't be a popular choice for most cars for much longer.

Well, you're talking about the UK. Over here diesels are the cheaper choice, as diesel costs less than petrol at the pump and you get significantly better mileage. I'm not going to debate the performance arguments, I'm not falling into that trap As for the environment, modern diesel engines are generally as clean - or even cleaner - than comparable petrol engines

Quote :

While petrodiesel's higher density results in higher greenhouse gas emissions per litre compared to gasoline, the 20–40% better fuel economy achieved by modern diesel-engined automobiles offsets the higher per-litre emissions of greenhouse gases, and a diesel-powered vehicle emits 10-20 percent less greenhouse gas than comparable gasoline vehicles.

EDIT: I'd very much like to see petrol engines become the better and wiser choice, but as things stand now I'd be inclined to go with a diesel engine if I were to buy a car.

Quote from obsolum :

Well, you're talking about the UK. Over here diesels are the cheaper choice, as diesel costs less than petrol at the pump and you get better mileage. I'm not going to debate the performance arguments, I'm not falling into that trap As for the environment, modern diesel engines are generally as clean - or even cleaner - than comparable petrol engines

They USED to be the best option cost wise, but considering the MASSIVE hike in Diesel prices (which are the same, or similar in most of Europe too), the cost differential has now become negligable.

As for cleanliness, CO2, maybe, particulates, no chance.

I drive a diesel purely because the way they drive (lazy) suits me, however, for me next car, I am seriously considering a petrol.

Quote from danowat :

They USED to be the best option cost wise, but considering the MASSIVE hike in Diesel prices (which are the same, or similar in most of Europe too), the cost differential has now become negligable.

I disagree. While the price of diesel at the pump is almost the same as that of petrol (still about € 0,50 cheaper per litre) you have to take into account that you can do a lot longer with each tank. Still the cheapest choice without a doubt, at least over here. That's why around 90% of the cars here are diesels. Petrols are for the rich who don't have to worry about paying for fuel

Quote from obsolum :

you have to take into account that you can do a lot longer with each tank.

Depends what you call ALOT I guess.

Quote from tristancliffe :

Well, they're not exactly good for performance, they're not exactly good for the environment, and they cost more to own and run in the long term (generally). They became very popular in the late 90s and early 00s, but petrol engines have been improving at a rate that will ensure diesels won't be a popular choice for most cars for much longer.

Performance diesels aren't rare though, and to me, tuned diesels are much more appealing than tuned up petrols, generally because the people tuning diesels do it themself, don't ruin a cars look and know what they are doing.

A performance diesel is still a contradiction of terms!! And do they still do it themselves? I thought most 'tuned' diesels were done via chipping (pointless on the road), or bolting on bigger and bigger turbos. Neither of which one can do properly in the garage as both require dyno sessions to perfect (unless you are chipping a 100% standard car, which would also be pointless). I remember the days when tuning an engine was taking it to bits in your bedroom, polishing the ports, pistons etc and putting it back together; that is doing it "themselves". Sending it away for work or just bolting on bits isn't doing it "themselves".

Quote from tristancliffe :

Sending it away for work or just bolting on bits isn't doing it "themselves".

Exactly. Which is what I am saying. Diesel tuners do it ALL themselves.

There's plenty of kits available for remapping my engine, but I've never seen the point. It's a diesel. The throttle response is delayed compared to a petrol engine, and I bought it to save money on fuel over the thousands of miles I do per year (which is set to increase if I can get this new job). I didn't buy it to be a performance machine, and if I'd wanted a performance traffic light drag racer I certainly wouldn't have bought a diesel

Although an R8 on the other hand...

Quote from Dajmin :

and if I'd wanted a performance traffic light drag racer I certainly wouldn't have bought a diesel

Although an R8 on the other hand...

Well torque is what you want for a traffic light drag, so a sooped diesel could be want you want, I know someone who has a Mk2 Golf TDi that easily runs 12's, running on biofuel of some kind(notsure what type) it can do 11's as did my uncles Mk2 TDi, bearing in mind they have no altered drivetrain, they are both FWD, and FWD suck at standing starts. That should give you an indication of how quick a diesel can be.


R8 V12 TDi? Yea, who doesn't want one.

Torque AT THE WHEELS is what you want. Depending on gearing, useable rev ranges and suchlike, a Diesel might be no better...

I'd much rather have a petrol R8. But I'd take some pursuading to buy such an expensive yet dull car.

Diesel tuners do it ALL themselves? They've installed dynos in their garden sheds, bought the software and hardware for remapping ECUs (and/or chipping), and built a bigger turbo themselves (as opposed to buying one that's bigger, but not at all matched with the flow characteristics of the exhaust, thus worsening performance)? Ha ha ha ha, yeah right.

Maybe my problem with the quick getaways is that I'm still not quite used to changing gear in the diesel and quite often get a big notchy shudder when it doesn't go right But while I do love that torquey I-can't-move-my-neck feeling, I don't reckon it's as fast from a start as the 323 was. Could be the extra weight of the derv engine, but I'd have thought the 25 or so horses difference would make up for that.

Quote from tristancliffe :

I remember the days when tuning an engine was taking it to bits in your bedroom, polishing the ports, pistons etc and putting it back together

At least it explains..

Quote from tristancliffe :

my ex-girlfriend

You're clearly an intelligent and well educated young chap, but when all's said and done, you are quite an odd fellow, arn't you Tristan.

No, no need to reply, there's no point in denying it, you woz robbed of the LFS Oddball Award 2009, for-sure.

I am odd, yes. That I cannot deny. Not all my exes are exes due to my oddness though!

Small willy then ?

Must be. After all, what other reasons, other than oddness and small willies, do girlfriends become ex-girlfriends?

As long as it's not both. Because you'd have no hope then

Ha ha!

(actually, she's my ex because she went to Turkey and fell for a Turkish man [that later turned out to be married])

Lol

Anyway, sorry to derail the conversation, i only logged on to check the progress of LFS, but couldn't resist an aimless quip.

Carry on


edit : sorry again, only noticed Tristans "Turkey" post after i'd posted this one. I was laughing at Dajmins pun, not your misfortune Trist

Quote from tristancliffe :

Must be. After all, what other reasons, other than oddness and small willies, do girlfriends become ex-girlfriends?

Amateur dramatics.

Thanks for your explanation anyway, although it was no help whatsoever and I'm still as clueless as I was before I read it. That probably isn't your fault though.

I stopped putting the coal there because all my music gear got mucky, but I'll give it another try.

http://www.hypermiling.com/

Best place to start Kev, but for gods sake don't buy a Pious or one of those shitty little G-Wizz's.

No, not that far back! Putting the coal in the boot is only for long journeys when you need more. You also have to take a short, dirty bloke to shovel the coal whilst you drive, which reduces boot space even further.