More Fuel Efficiency When Driving At Higher Speeds?

[omri617 18]

I know it sounds strange , but I can swear I noticed that my car consumes less fuel (long journeys 150 KM) , when driving at high speeds 110-120 kmh (RPM more likely to be 3000+)

, less than when driving 85-95

Is this technically possible??

I run 1.6 management with DKZ engine..

[Anthony 1,003]

Whilst the engine will be more or less effiicient at different revs, aerodynamics and the power needed to push the car through the air will almost certainly mean that it's consuming more fuel at 120kph than it would be at 90kph.

 

I suspect that any additional economy you're seeing is thanks to sitting at a steady speed cruise on light throttle at 120kph, whereas you're probably accelerating and braking more when you're on slower, more congested roads. As anyone with a trip computer that displays live MPG readings will confirm, acceleration has a big impact on economy as you're using a lot more fuel whilst accelerating and under heavy load than you are on a steady speed cruise on a light throttle.

[omri617 18]

Thanks for the reply firstly ,

On the contrary , when driving 90 I make it more "eased" and almost no traffic lights cause i travel mainly at night.

I was thinking maybe it's related to the AFM and the throttle position. maybe when the RPM on the 2000 , the mixture of fuel and air is not so "correct" (due to the mix and mis match in some components in my car) . And when it's going up towards the 3000 RPM , things workout together better..

[GLPoomobile 958]

The thing is, measuring differences in economy is actually quite a difficult thing. Without having a modern trip computer that can accurately measure it (and some will argue that they aren't 100% accurate anyway), and also show you 'real time' changes in MPG, it's even more difficult. If you do the exact same trip every day, and drive in the exact same way on every trip, and the conditions are exactly the same on every trip, then over time......over quite a long time......you can get a fairly accurate view of your average MPG. But even doing the same journey every day, the conditions are never the same, and you won't drive exactly the same every time.

 

When you've watched real time MPG changes whilst driving a modern car (I'm quite anally retentive with this ) it's actually a real eye opener to see just how massively it can fluctuate under various conditions. Incline (the sort of incline that you can barely perceive as you're driving), temperature, road surface, head winds and even cross winds will make a bloody huge difference to real time MPG.

 

So what I'm saying is, what you perceive as a difference in economy under different driving cruising speeds may possibly be totally wrong, simply because you can only go by average MPG per tank and every journey will be different. And that's just not accurate enough.

 

Now, having said all that, of course it's entirely possible that it IS consuming less fuel at 110-120kph than at 85-95kph. You'll often find that the sweet spot for best economy lies somewhere within that range, and it'll be different for each car, engine and gearbox combination. For a 1.6 GTI, I honestly doubt it is more economical at the higher speed, but I guess it's possible. I'd certainly expect it to become less economic above that speed.

[kyepan 291]

aerodynamic efficiency - increase this and your high speed fuel consumption will fall

[welshpug 1,661]

Depends on terrain massively, especially if you are on a long gearbox, i have been driving s c5 hdi and it us better at 56 and over 2k rpm than below that as it is off boost and labouring.

 

I have found that going through the gears at light throttle is far more efficient than low rpm.

 

Fact it weighs over 1500 kg doesnt help...

 

But damn its quiet and comfortable!!

[omri617 18]

That's comforting to hear this ,I was expecting answers like "WTF" and "don't be silly"

I run 1.6 gearbox , Thought about changing the 5th gear to a longer one (1.9) , who knows ..

Edited April 6, 2013 by omri617

[welshpug 1,661]

Doesnt work like that as its identical, its the final drive that differs.

 

Imo you cannot compare mpg till you have it running properly on the correct ecu.

[Tesstuff 222]

That's comforting to hear this ,I was expecting answers like "WTF" and "don't be silly"

I run 1.6 gearbox , Thought about changing the 5th gear to a longer one (1.9) , who knows ..

Why run a car like this if mpg is even a consideration? Get on the B roads(or your equivalent) and thrash the arse off it.

 

The day you then worry about the mpg after your hoon is the day to sell it.

[pug_ham 244 3 Cars]

I run 1.6 gearbox , Thought about changing the 5th gear to a longer one (1.9) , who knows ..

They have the same fifth gear ratio, just a different final drive ratio.

 

g

[Batfink 201]

no matter what its having to push through the air that ruins fuel consumption. My audi is massively more efficient at 65-70mph than 75 or 80mph

Fuel consumption is severely affected by driver input though which is why its better on cruise control

[omri617 18]

Why run a car like this if mpg is even a consideration? Get on the B roads(or your equivalent) and thrash the arse off it.

 

The day you then worry about the mpg after your hoon is the day to sell it.

 

The thought behind it all , it's not "how to reduce mpg" but more like figuring out mixture lacks maybe ..

I put a lot of money in my car , especially where I live where info about the car is limited and parts are almost impossible to find

[Simes 248 2 Cars]

Fuel consumption is severely affected by driver input though which is why its better on cruise control

Funny you mention that I find the cc on the E91 more aggressive getting up to my European cruising speeds than my right foot. Watching the real time mpg guage it shoots round to 16mpg!

[Batfink 201]

I use cruise control to cruise or make minor adjustments in speed :-) but my Audi will do the same when accelerating using the buttons. I still average about 5mpg better by using the system. It's annoying as I've tried to be better than a computer and failed

[DanteICE 72]

I use cruise control to cruise or make minor adjustments in speed :-) but my Audi will do the same when accelerating using the buttons. I still average about 5mpg better by using the system. It's annoying as I've tried to be better than a computer and failed

I wish the 205 had cruise control, the long journey back home from Uni kills my foot.

 

What about using an AFM to give accurate reading of fuel efficiency?

 

Geoff

[Batfink 201]

You would have to monitor the flow through the fuel line and the fuel return. Calculate the difference over time. I doubt the Ecu is any use for logging any data

[omri617 18]

I don't think I will get into measuring really , just a thought I wanted to share .. ​

[shorty_15-92 1]

They have the same fifth gear ratio, just a different final drive ratio.

 

g

 

Am i right in thinking the diesel box has longer gears?

[pug_ham 244 3 Cars]

Am i right in thinking the diesel box has longer gears?

It has different gear ratios to the GTI obviously but mainly due to the longer final drive, it has the same fifth gear (0.757:1) as the Mi16 box which when fitted to a 1.6 box gives the same fifth as a 405 SRi box.

 

g