What Revs for fuel efficiency?
- Thread starter hsyben
- Start date
Scottish Borders
In any ICE peak torque is usually the best mean specific fuel consumption...but I suspect that's not what you were asking?
I suspect you were asking what's the best fuel economy measured in miles per gallon..
Since drag is in simple terms the square of the speed it will be as slow as possible in a gear that is way less than peak torque
I suspect you were asking what's the best fuel economy measured in miles per gallon..
Since drag is in simple terms the square of the speed it will be as slow as possible in a gear that is way less than peak torque
Shropshire, UK
Having had a 2.5i and then a 3.0si the best thing you can do for fuel efficiency in the 2.5i is fit a 6 speed gearbox 
Under 3k is my rule of thumb for petrol cars, although I never noticed that much of a difference on an economy run in the 2.5i rather than pressing on. Maybe 5-7mpg difference overall. It would manage 40mpg+ on a long run though.
Under 3k is my rule of thumb for petrol cars, although I never noticed that much of a difference on an economy run in the 2.5i rather than pressing on. Maybe 5-7mpg difference overall. It would manage 40mpg+ on a long run though.
Revs are directly related to road speed. The rule of thumb used to be get into top gear as quickly as you can and use the lightest possible touch on the throttle pedal to get the revs and therefore speed that you want without labouring the engine.
I'm not so sure this is still true with modern fuel injected engines as planting the pedal doesn't dump a load of petrol into the engine like a carburettor would do.
You could always keep an eye on the computer?
I'm not so sure this is still true with modern fuel injected engines as planting the pedal doesn't dump a load of petrol into the engine like a carburettor would do.
You could always keep an eye on the computer?
I don't have any scientific data but I remember back in the 70s and 80s manufacturers had to quote fuel consumption for Urban use, constant 56mph and constant 75mph. Every car on the market was far more economical at 56 than 75 and I'm guessing your 3,000rpm in 5th is about 70mph based on my 5 speed E46 325ti with the same engine.
As B21 has pointed out drag is the enemy of economy so you'd probably get best fuel consumption at a steady 45 or so. But if you are bored enough to try hyper-miling let the speed creep up going downhill and bleed off gong uphill - just make sure you stay awake!
Alternatively avoid commuting and enjoy the straight 6 performance whenever you are in the mood. That's what I did with the 325ti, and it still averaged more than 32mpg over 23k miles which seemed pretty impressive to me.
As B21 has pointed out drag is the enemy of economy so you'd probably get best fuel consumption at a steady 45 or so. But if you are bored enough to try hyper-miling let the speed creep up going downhill and bleed off gong uphill - just make sure you stay awake!
Alternatively avoid commuting and enjoy the straight 6 performance whenever you are in the mood. That's what I did with the 325ti, and it still averaged more than 32mpg over 23k miles which seemed pretty impressive to me.
I got an average mpg of 35.4 when cruising at 60-70 mph, with the top down. 60 mph (about 2500 rpm) was comfortable and 70 mph was blowy. I don't know how the on- board flight computer calculates average mpg but 60/70 didn't seem to make much difference. I find that I don't drive very fast in my Zed because it is so low to the ground that even 50 mph feels fast off the motorway. Though it is fun to put one's foot down occasionally to get away from a prat who is determined to crawl up one's arse!
What a fun car?
What a fun car?
At the summit of the picturesque fens
It takes data from many places and sensors. I have just rewired a Z3 which had an OBC. The amount of signals related to the fuel data was incredible.
Lowest ive ever had was 13mpg on a trackday at spa. No idea what the highest was!
Back when a friend and I owned MX-5's I managed to get better mpg out of my 1.8 NA by hypermiling it from Leeds to Shropshire, coasting behind lorries, going up hills really carefully/slowly. Managed a whole 35.5mpg average over the ~100 miles. Best he ever managed was 34mpg I think, which was really amusing as on paper his had variable cams and things to make it more fuel efficient.
Gotta love AI, it can tell you the answer, but if you don't understand it and regurgitate it in your own words, it may sound good but is just gibberish.
Having just got home after four an a bit hours on five motorways at an average speed of 61 mph, I managed about 41 mpg. The key to getting the best fuel economy in my experience is not braking, try to maintain momentum by anticipating the road ahead. the big killer is accelerating and so if you are going quite fast in the outside lane you are continually braking and accelerating and that kills furel economy.
At uni, we did a lab on brake specific fuel consumption on a petrol engine and dyno, which could vary the load so as to determine when the engine was a maximum efficiency, we produced a graph.
Low load → poor efficiency → increasing load → improving efficiency → minimum BSFC, until to much load reduces BSFC
Having just got home after four an a bit hours on five motorways at an average speed of 61 mph, I managed about 41 mpg. The key to getting the best fuel economy in my experience is not braking, try to maintain momentum by anticipating the road ahead. the big killer is accelerating and so if you are going quite fast in the outside lane you are continually braking and accelerating and that kills furel economy.
At uni, we did a lab on brake specific fuel consumption on a petrol engine and dyno, which could vary the load so as to determine when the engine was a maximum efficiency, we produced a graph.
Low load → poor efficiency → increasing load → improving efficiency → minimum BSFC, until to much load reduces BSFC
Alright alright that’ll do love….put yer knickers on and go and make a pot of tea….
