Gridlock Mikey

Be in 3rd gear with the engine revs running at about 3500/4000 ish on the edge of the power band on a dual carriage way or 4th gear 1750/2250 rpm engine labouring slightly, no power to call upon (remember dual carriage way so not likely to need any)but just as quick.

Which way uses more fuel? the engine spinning quicker but with less to do or the slower spinning engine that is labouring due to gearing.

Comments invited!

Just a thought 'cos sometimes i change up ('Cos the exhaust sometimes ) only to release the clutch and change straight back down again. I think that the car is happier running higher revs than labouring, it feels safer to, having the power there.

Pointless thread i know but how do you explain it?

Mikey

brickboy

Good question -- glad to see I'm not the only one that worries about driving habits.

It's better for economy to be cruising at 2000rpm in 4th, but obviously if you need to react quickly to changing road / traffic conditions with a burst of acceleration ;-) then you need to be in 3rd gear at around 3000rpm. However being at 3K rpm is going to use more fuel (even though throttle opening is about the same) and will be wearing the engine quicker, due to higher rpm.

For what it's worth, I usually cruise in the highest gear the car will pull, providing that the revs are always above 2K (to avoid lugging the engine at low rpm, which is far worse than revving it hard) .... unless I'm waiting for an overtaking opportunity, in which case I'm in 2nd or 3rd ....

STi wanna Subaru

iTrader: (1)

Just a point regarding Ecommony. I find that I get better mpg when most of my driving is at 80mph in 5th @3000 rpm than 60mph and lower rpm. To answer your question I think 4th gear would provide better mpg in the situation you described.

CharlieWhiskey

Mikey!

Best economy will be just before the turbo spins up, as long as the engine is not labouring too much. Sitting on a dual carriageway between 2000-3000 revs in fifth, depending on conditions overtaking etc. should be the most economical. (Dropping to fourth if you need to pass anything).

Once you start to get any decent boost then the economy goes out the window! If you are sitting on a dual carriageway in third then then you either in traffic or about to scare someone ****less by blasting past them

Gridlock Mikey

Is the general concensus that labouring slightly in 4th or 5th is better than sitting on the edge of the powerband for not only fuel consumption but also engine wear ?

Apart from not getting anywhere quickly, does labouring excessivly damage the engine?

Just wondered

Mikey

fast bloke

AFAIU economy is not entirely dependant on revs, but on the amount of work the engine needs to do. You can test this by getting a BM with a momentary fuel consumption guage. Drive along a flat peice of road at steady 60 in 3rd, 4th or 5th gear, and the needle stays around 30ish. Floor it in any gear and the needle drops to 10. Higher revs will wear your engine more quickly, so for best economy, accelerate as sharply as you can in the lowest gear, (you get 10 MPG in any gear, so less time spent accelerating will save fuel) and cruise in the highest gear where the car stays over about 2000 RPM

Gridlock Mikey

Hmmmmmm!

Best not turn the engine on then, maybe roll to work

Mikey

Jolly Green Monster 2

I also change up to 4th unless it labours lots (read shaking dash)

I also noticed that with Optimax in tank is labours at a lower RPM than before therefore making using higher gears and lower RPM better....

PS: In no way connected to Shell, this is not an advert

NBW

Just to confuse things, engines 'generally' are working more efficiently at 3K than 2K revs....so changing up a bit earlier doesn't necessarily have an huge impact on fuel consumption.

IMHO more impact on fuel economy is to be had from using 'acceleration sense', e.g. anticipating what's happening ahead, and easing off the gas, rather than staying on and having to use more brake.

Every time you brake, you use fuel twice - once to get you up to the speed from which you started braking, and once again to get you back up to speed when you've finished braking.

Cheers
Tim

Floyd

iTrader: (9)

Tim's right of course, anticipation is the best fuel saver. I did read somewhere that some Swedes studied how to drive economically and tried all methods. They decided that engines were most efficient at 3/4 throttle and under load so they used 3/4 throttle in each gear until top is reached, then backed off to steady state cruise. This doesn't work in built up areas or in heavy traffic though.

I tend to use top gear at 2k revs on the daily commute, which is in mild to heavy traffic. This gives me 300 miles to 50 ltrs. Boring, I know but no other choice.

F