Let s say torque peaks at 2400 rpm and power at 4500 rpm , redline starts at 5000 rpm. Engine is a 1.7 turbo diesel...

Well thats the problem , these twats at opel didnt revealed any consumption diagrams even after 20 years , i can t get the r from the BSFC and im too lazy to calculate everything from the begining as i need this info in a few hours

My guess was somewhere in between 2400 and 4500 like 3000 but that sound kinda weird for a diesel

knowing the name of the engine might help
en.wikipedia.org/wiki/Circle_L_engine

Generally peak efficiency is near peak torque rpm and 90% load.
However, if you keep the engine in that range you will accelerate.
At a constant speed the best you can do is select the highest gear that doesn't lug the engine, probably around 1500rpm, maybe slightly higher.

Tc4ee1 by isuzu made for opel and mazda

Where the hp is lowest but there's the most torque

Coast in neutral whenever you're not on an incline.
Accelerate, put it in neutral, coast until you're too slow,repeat.
Diesel engines use almost no fuel during idle.
Always drive in the highest possible gear that doesn't lug the engine down.
On hills try to stay in the engine's peak torque range at all times.
Don't try to accelerate on a hill. It wastes a ton of fuel. Try to only press the pedal so much that you keep your current speed.
Even just a little more throttle can use 25-50% more fuel while not notably accelerating at all.
t. 60 MPG in a 17 year old terbodiesel wagon

Thats why i ppsted this , for me its more logic to keep the engine reved at 2000 rather than 3000 like most university teachers told me

Thanks

Makes sense, thanks. Is there a method analogous to petrol vehicles?

I have read this also but I can't find any sources to back it up, As he said when driving normally I shift about 300-500 rpm above redline which is at 6k. 4cyl with 105hp.

Coasting and accelerating with an idling engine is stupid when modern engines inject 0 fuel furing coasting in gear. Neutral coasting can be bad depending on the car.

Best way to attack a hill is to accelerate before it, and shed the speed while going up it. In an 80 zone, accelerate to the speed limit on a level piece of road, and aim to have reduced that speed to about 50 at the top of the incline.

Never touch the brake pedal. Braking is wasting energy. Look ahead, anticipate.

When possible, slipstream behind bigger vehicles. I'm getting 24km/l (55-60mpg) highway in my gf's 1.0 petrol Suzuki Splash with that technique.

Yeah, don't drive around at a sustained 3000rpm. That will not be good for an engine in the long term. Throttle position plays a key part in fuel consumption. The idea cruising rpm would be whatever allows the lowest rpm and smallest throttle opening at once in order to sustain your speed.

The highest gear with the lowest RPM possible without lugging the engine

>drive a Boxster
>cruising at 100 km/h on the highway
>engine revving at 3000rpm all day long

I feel bad for S2000 owners on highway trips

The efficient burn of the fuel to produce energy may be at engine maximum torque which is also a certain rotational speed (usually). At that moment the multiple of unique torque times unique speed gives a specific power output which is also unique. Then most were to prefer to connect that engine at that fixed and economic performance to a continuously variable transmission and the questionner is right to suggest it's going to sound high revving. Such a vehicle will accelerate and move against wind resistance with a fixed power. Someone content to accelerate taking a very long time and finally going very slowly against the air (for the same vehicle size, tyre friction etcetera) will arrive more economically and apparently late. The problem is that to make it efficient, he or she is going to need a small engine deployed only at max torque and when he reaches a significant hill - the vehicle won't work.

The reality is else than a technique of changing gears - one really needs to change out the motor. I know we're educated to suppose the gearbox takes care of the problem, yet then, as the questionner remarks . . . we're rarely or never using the engine at it's most efficient point - becaaaaaaaause . . . . they're all over-powered (to be ready and capable of going up hill). You think this mad? It is! If you accelerate away from the stoplights with a typical 4000 rpm torque and efficiency (which it is), by changing gears, you'll notice you've slammed up behind the car in front. Everyone, but everyone is obliged to accelerate slowly, well out of the efficient range to stay on the road and behind the slowest and most efficient. When I mention "slowest" one is careful with the term, because they may accelerate slowly yet have a very high speed once cruising (airplanes and trains come to mind).

Trains do it well . . . really. They pick a schedule, choose an engine for a specific cruise speed on the flat just able to overcome friction and airdrag . . . . then they accept (tolerate) whatever acceleration will result when leaving the stations . . . . then when they meet an incline - they "change out the motor" to more correctly stress the exploitable torque . . . i.e. they add more locomotives as just and only necessary, then unhitch them at once. Any other idea is inefficient, wasteful and due to lack of patience with the hitching and unhitching.

There are canny people who have really understood this point and there are engines which can shut down a few cylinders to put the remaining pistons to their maximum torque, yet the high revving noise is unpopular.
Wikipedia explains "Variable deplacement" engines rather well. Take a V8 then only run one half or make the combustion chambers variable in size. Do the customers care enough, that much about economy? Apparently not as each regular vehicle manufacturer offers something that "people" turn down.

Unlike a train it's less convenient to drop off the excessive motorisation from a car once an hour - physically. Rockets do it and it is, really crucial to have fuel economy in their field, in stages as the speed/acceleration requirement reduces. Some planes can do something similar; some pilots of three engined jet airliners flew on only two (which seems an "obvious" economy - aren't I just silly?), however those two are going to be working "hard" at higher thrust (not maximum, yet not far off). Those two will burn more fuel per hour yet more efficiently while they do, just beating a three running engine configuration overall.

I hope those aware of this 'story' will tolerate my oversimplification and notice that I attempt to answer the question for clarification rather than ignore the topic of gearshift. Most people simply can't shift up at efficient rpm using their overpowered cars (ready for hillclimbs) without slamming into the cars in front or ripping off rubber on their own tyres.

The thing is, while coasting in gear the engine breaking will slow you down significantly compared to coasting in neutral.
The distance you manage to coast further while in neutral by far offsets the amount of fuel engine braking and fuel cutoff saves.

but well not all cars have 0 consumption while engine breaking, at least thats what i'm thinking, and thats why i'm all paranoid and coast in neutral

highest gear at the lowest rippums will get you yout best mpg

>coasting in neutral
yeah, just like this gentleman:
youtube.com/watch?v=6N4tLAAy5Fg

This guy drives like an animal, i feel for that car mayne

kek
my civic needs 3k rpm in 5th to maintain highway cruising speed

to achieve maximum fuel conservation you are supposed to be in the highest gear and the lowest revs possible without your car feeling powerless or as if its getting choked, while respecting the speed limit

for example my shitty diesel got peak torque from 1500 to 2500

I try to keep it around 1500-1800 when cruising and downshift when it goes bellow 1500. i guess it depends on the engine, since mine is a crappy NA piece of shit it also doesnt consume a lot of fuel when im doing 120km/h somewhere between 2500 and 3000rpm feathering the throttle