Optimum gear to use for maximum MPG
Discussion
I've been wondering this recently about turbo engines. Is it better to run at low rpm but high boost and hence torque or higher rpm and less boost/torque? On a NA engine I can feel where it is most happy but the turbo engine allows much more flexibility of operation and I'm not sure which is best yet.
FWIW, my car - a small capacity turbocharged engine - has an auto gearbox. When pootling for economy, I can drive up to approx 40mph without really exceeding 1500rpm. The gearbox keeps the engine in the 1100-1500rpm band. Even so, driving around town the economy doesn't exceed 30mpg.
On the motorway, the long 7th gear (2500rpm at 75mph) does help economy, getting an average of 42mpg.
On the motorway, the long 7th gear (2500rpm at 75mph) does help economy, getting an average of 42mpg.
Dyl said:
FWIW, my car - a small capacity turbocharged engine - has an auto gearbox. When pootling for economy, I can drive up to approx 40mph without really exceeding 1500rpm. The gearbox keeps the engine in the 1100-1500rpm band. Even so, driving around town the economy doesn't exceed 30mpg.
On the motorway, the long 7th gear (2500rpm at 75mph) does help economy, getting an average of 42mpg.
A 2011 Seat Ibiza 1.2TSi DSG incase anyone was wondering On the motorway, the long 7th gear (2500rpm at 75mph) does help economy, getting an average of 42mpg.
Pixelpeep said:
Dyl said:
FWIW, my car - a small capacity turbocharged engine - has an auto gearbox. When pootling for economy, I can drive up to approx 40mph without really exceeding 1500rpm. The gearbox keeps the engine in the 1100-1500rpm band. Even so, driving around town the economy doesn't exceed 30mpg.
On the motorway, the long 7th gear (2500rpm at 75mph) does help economy, getting an average of 42mpg.
A 2011 Seat Ibiza 1.2TSi DSG incase anyone was wondering On the motorway, the long 7th gear (2500rpm at 75mph) does help economy, getting an average of 42mpg.
If I had a rev counter I would know what the change up points were - however Ford included an aural warning system on the Endura-E - when it makes too much tappet noise change gear. Which was nice of them. They also threw in a sensible downshift indicator - in that if the car slows down going up a slope or into a headwind it's time to drop a gear. Sort of like the EU mandated shift lights before they were thought of. In terms of fuel economy, it's acceptable if the engine is quiet and making timing chain tinkly noises and bad if it's emitting a raspy roar. Anything between is meh.
But the actual solution to this is the 1.9 Citroen/Peugeot turbo diesel. It does the same amount of miles (loads) to the gallon no matter what gear you are in. Therefore you don't have to worry...
But the actual solution to this is the 1.9 Citroen/Peugeot turbo diesel. It does the same amount of miles (loads) to the gallon no matter what gear you are in. Therefore you don't have to worry...
d I hate you.
A friend told me his wife used the RRRRRRRRMM and change, RRRRRRRRRM and change, method of deciding when to change up, regardless of whether she was driving uphill / downhill or on level roads, and whether or not the car was picking up speed at an alarming rate, or the engine was labouring to the point, it was trying to climb out of the car. he said he did not think that she had ever grasped the driving a car thing properly and drove by rote!!
Passat Bluemotions like many cars these days have a gear change indicator, but it seems to want the driver to change up far too early. so I ignore mine, and just change up when it `feels' right.
Passat Bluemotions like many cars these days have a gear change indicator, but it seems to want the driver to change up far too early. so I ignore mine, and just change up when it `feels' right.
Vyse said:
How about accelerating too slowly, does this also kill MPG?
In my big petrol V8 auto cars I found that accelerating slowly made no improvement at all to fuel economy so I might as well give it some boot. In my smaller manual cars it seems to work best with reasonably gentle but not glacial acceleration. The improvement is so minimal however it's not worth the displeasure so giving it some is still the preferred method.The biggest improvement you can make to economy is by anticipation, planning and staying off the brakes. The actual method/rate of acceleration doesn't seem to make a massive difference.
a test was run a while back that showed (on the car they used, can't remember what it was) that using the most throttle possible, whilst not activating open loop fuelling, and changing up as low as possible was the best way to accellerate. Doing this opened the throttle wide which reduced throttling losses, and getting out of the lower gears early reduced the total number of revs, and thus the amount of fuel used
It you want to use less fuel, stop worrying about which gear you are in and focus instead on the brakes. Every time you touch that pedal you are turning motion in to heat - motion that you burned valuable fuel to gain. You'll then have to burn more fuel to get back to the previous speed again.
Smooth flowing driving will save more fuel than anything else you can do.
Smooth flowing driving will save more fuel than anything else you can do.
5lab said:
a test was run a while back that showed (on the car they used, can't remember what it was) that using the most throttle possible, whilst not activating open loop fuelling, and changing up as low as possible was the best way to accellerate. Doing this opened the throttle wide which reduced throttling losses, and getting out of the lower gears early reduced the total number of revs, and thus the amount of fuel used
how do you know when the ECU is transitioning between closed/open? Just guesswork, i.e. trying to keep throttle below 75% or is there more to it?edit: some info
Application in use
bikeboy said:
All of the above test and practical restrictions mean that the Closed Loop systems usually operate at low throttle openings (below 20%) and below 50 to 60% of max RPM. Above those throttle and RPM points the system goes back to Open Loop operation, running off the fuel maps stored in the ECU.
http://www.bikeboy.org/open_closed_loop_efi.htmlEdited by budgie smuggler on Friday 14th February 11:35
budgie smuggler said:
how do you know when the ECU is transitioning between closed/open? Just guesswork, i.e. trying to keep throttle below 75% or is there more to it?
Plug a computer/phone/whatever in the diagnostics port and ask it? Fuel/air ratio is one of the standard OBD2 queries. kambites said:
budgie smuggler said:
how do you know when the ECU is transitioning between closed/open? Just guesswork, i.e. trying to keep throttle below 75% or is there more to it?
Plug a computer/phone/whatever in the diagnostics port and ask it? Fuel/air ratio is one of the standard OBD2 queries. budgie smuggler said:
5lab said:
a test was run a while back that showed (on the car they used, can't remember what it was) that using the most throttle possible, whilst not activating open loop fuelling, and changing up as low as possible was the best way to accellerate. Doing this opened the throttle wide which reduced throttling losses, and getting out of the lower gears early reduced the total number of revs, and thus the amount of fuel used
how do you know when the ECU is transitioning between closed/open? Just guesswork, i.e. trying to keep throttle below 75% or is there more to it?edit: some info
Application in use
bikeboy said:
All of the above test and practical restrictions mean that the Closed Loop systems usually operate at low throttle openings (below 20%) and below 50 to 60% of max RPM. Above those throttle and RPM points the system goes back to Open Loop operation, running off the fuel maps stored in the ECU.
http://www.bikeboy.org/open_closed_loop_efi.htmlEdited by budgie smuggler on Friday 14th February 11:35
maybe its different on bikes? On Vauxhalls op-com can read the current state (ie open loop or not) but that's probably beyond the average driverGassing Station | General Gassing | Top of Page | What's New | My Stuff