Fuel Economy

[Ste]

In a diesel, 2.0 TDI, is it better to go up a hill at say 3k rpm as apposed to 2k rpm to save fuel?.

I was just wondering if the engine being under load at low revs used more fuel than being under load at higher revs?.

http://faculty.gvc.edu/kgannon/ProfessorFrink1.gif

[saxova]

Ive always wondered this..

[Morgan_VTR]

Good question. Surely it would be the same principal for a petrol car?

[Tommo87]

Look at the trip computer they usually tell you the mpg figures.

[Ste]

The real time mpg has a lag and doesn't give a reading that i can really get much info from without writing each one down and doing the maths, and i want to know specifically what gear would be best for certain hills to get the best overall MPG.

[Scribbles]

Generally you'd get best fuel economy between 2000-2500rpm at around 35-40% load.

Difficult to work out how much load you applying in the car but just doing this lab at uni and fuel consumption at 50% load at 2000rpm and 3000rpm in a VW 1.9TDI engine is very similar and better than 25% or 100% load in both cases.

[Viper]

well i was going to say check the instantaneous MPG reading...

but bollocks to you

[dannyboy2005]

I would guess climbing at 3K revs would be more efficent.

Wouldn't have to put your foot down to keep the revs where they are as the further up the hill you get as the torque is there so its a constent acceleration wise.

[Paul]

*Awaits Adsayer*

[Barry123]

*Awaits Adsayer*

Now then,

Actually ste this is one of the drawbacks of the Cruise Control System (explain how this is relevant in a second)... When you're on a flat road it's a perfectly good system and the easiest way to achieving high mpg on a motorway - provided you can maintain your speed for the entire MpgMax. run. However when it comes to even moderate hills the the cruise control system of maintaining the set speed to achieve best economy failz. This is because it's actually better (numerous research backing this up in Research Journals n shit) to gradually build up speed when approaching the hill then allow that speed to gradually decline as you make your ascent back to the original speed. This doesn't mean smack it to 100mph just to let it return to 60-70mph at the top... raise to say 75-80mph then moderate the throttle so that you lose say 5mph halfway up and then the remaining 5mph on the remain half of the incline.

when you're comparing going up a hill at 2k rpm to 3k rpm... it's better to do it at 2k rpm as you're going slower (thus more economical).

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EDIT: you mean is it better to say go up in 5th at 2k than 4th at 3k yeah?

[dannyboy2005]

EDIT: you mean is it better to say go up in 5th at 2k than 4th at 3k yeah?

Yea Dude!

[Barry123]

5th... 2k rpm is where peak torque is on a diesel engine therefore roughly at the highest brake specific fuel consumption.

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[dannyboy2005]

G33k

:d

[Paul]

I knew you would come adsayer, i knew it.

[Luke]

Sayer strikes again.

Thanks for that information Ads.

[Ste]

Excellent info, cheers!