Consider an average modern common rail turbo diesel car that develops peak torque typically around 2300 rpm.
If you are driving on relatively flat terrain at 30mph would you use more fuel :
a) by driving in, say, 3rd gear with the revs around 2000
b) by driving in, say, 5th gear with the revs around 1300
One argument says that a) would prove to be more fuel efficient because the revs are closer to the peak torque output and therefore requires less pedal pressure to maintain the speed, but another says b) because the revs are lower thus automatically using less fuel and you’d still have more than enough torque at those revs to maintain the speed, except for all but the steepest inclines.
Who is right and why?
Oh and apparently b) will increase the engine component wear because the engine has to work harder.
it wont make much of a difference to which gear you use but you’ll use a little bit more fuel as the engine is turning over quicker in 3rd than 5th, but in 5th the engine is turning over slower than in 3rd but if you need to respond to a situation i.e need to stick your foot down , the engine will most likely bog down and say go screw, so you end up changing in to a different gear and then stick your foot down, this is because of 2 things
1 at 1300rpm the turbo possably won’t start to work till 1500/2000 rpm
2 on a modern derv the accelerator pedal is connected to the ecu not the engine, you request 100% throttal to the ecu, the ecu inject’s more fuel in to the engine the amount is dertimened by pedal position, fuel tempture, and the amount of air and tempture of the air and engine speed, so the ecu decides how much fuel is put in, it won’t flood the engine with fuel as that waste’s it. why do you see an old direct injection devr smoke under heavy load and a cdti dosen’t smoke as much under heavy load.
but it all comes back to the same thing use the right gear for the right situation for the best engine responce.
Sorry meant to say 4th not 5th. The turbo comes in a lot earlier than 2000 rpm, and certainly on my car it comes in around 1250 rpm (ish) although mine is remapped and that was adjusted. But the point is that the terrain is relatively flat and you are just cruising along - I’m not talking about suddenly needing to accelerate to x mph, I’m just after knowing
which one would use more fuel?
would driving at 1300 rpm increase wear on engine components more than driving in 3rd at 2000 rpm?
I certainly can’t see how the second one can be true as the engine isn’t turning at much more than tickover.
Once a donkey is missing a hind leg, he will still have the last word.
Two very easy questions.
Can you delete that word please Dave. He will no doubt search for it to see who is talking about him and I’d rather he kept his worthless beak out of my threads.
i should say driving in 4th would use slightly more fuel but only if when in 5th the engine is not labouring
Rob K:
would driving at 1300 rpm increase wear on engine components more than driving in 3rd at 2000 rpm?
no, but as above if the engine is labouring it will increase engine wear, as you are putting a hell of a lot of strain and pressure on the bottom end of the engine
and what the ■■■■,are you and dieseldave on about (i’m assuming i’m the profuse poster)? could someone enlighten me please, as i am not easely offended
I admit to knowing naff all about modern diesel engines but am learning fast… like yesterday when I failed to replace the oil filler cap on the wifes 325TDS, wot a bloody mess
I learned to check its on before closing the lid
raymundo:
I admit to knowing naff all about modern diesel engines but am learning fast… like yesterday when I failed to replace the oil filler cap on the wifes 325TDS, wot a bloody mess
I learned to check its on before closing the lid
Oops! You know who will be here soon with the story about dipping Caterpillar engines while they are running. It’s true, but not normally on Lorries, only heavy plant.
Please take a moment to re-read the posts and Rob K’s request.
