Shifting @ lower RPM = bad for fuel economy?

[xenonkuraz]

I've just had a comment from a friend who says that I may be getting less KM's out of my tank than his due to my low-end RPM shifting (1.5-2k RPM). We both drive DC2 Vti-R's; same tank capacity.

He said that apart from using a different fuel to him (I use V-Power, he uses BP Ultimate), it may be better to shift at a higher RPM, i.e. 2.5-3.5k RPM.

True?

I tried a full tank of BP Ultimate (literally full), and it got me less KM's than the V-Power did.

Could I be running rich? My smoke colour seems normal...

[panda[cRx]]

it's generally better to be in higher gear and lower rpm

but it's hard to compare fuel consumption between cars as the engines will be different ages with different condition and will have travelled a different amount of kms. not only that the routes you drive everyday are different too, not to mention how the car is driven
you havent even mentioned what the 2 different fuel consumptions are

[xtat1k]

V-power, usually used to get me more km's but bp runs smoother but less km's.
basically, you cant really compare from one dc2 > dc2 ; they're all different (engine wise)

[blk_shadow]

Shift Around 3k Is The Best, If You Just Want To Cruise Along.

If Below That And The Engine Is Warmed Up, The Load Might Be Heavier For The Engine To Match The Speed With The Higher Gear Ratio

[dsp26]

no gear/rpm combo is better for shifting as it depends on speed vs load.

on flat road or at highway speeds the higher gear/lower rpm combo is better for efficiency.

however in city/hill driving its better to be in a lower gear and revving higher as:
- it reduces load on engine
- quicker to get to speed you want due to gearing

Although this should be common sense, ECU consult hook-up on my previous car backed this up when say in 4th gear/~70km/h on an incline... no matter how much i pressed the accel pedal there was no increase in acceleration despite injector duty cycle increasing and measured KM/L getting worse also.... yet when you shift down into a more efficient gear to suit the incline and rev it, it uses less fuel/duty cycle due to the resulting less load.. .you could even maintain 6krpm on the lower gear (while not on load) and it had less injector duty cycle & better KM/L than flooring say 4th/5th gear while on load

[TJsol]

higher gears and lower rpm shuld get u more km/s. The petrol used in your car also wil depend on how much km/power u get out of your car to.

i would say keep using the v-power n u shuld b fine.

[xtercii]

1.5k - 2k? That's way way way too low, and you are probably putting a lot of strain on your engiine.

Try shifting at 3.5k - 4.5k, it's more fun to drive and will probably give you the optimum fuel consumption (at least with my car).

[czy_sol87]

no gear/rpm combo is better for shifting as it depends on speed vs load.

on flat road or at highway speeds the higher gear/lower rpm combo is better for efficiency.

however in city/hill driving its better to be in a lower gear and revving higher as:
- it reduces load on engine
- quicker to get to speed you want due to gearing

Although this should be common sense, ECU consult hook-up on my previous car backed this up when say in 4th gear/~70km/h on an incline... no matter how much i pressed the accel pedal there was no increase in acceleration despite injector duty cycle increasing and measured KM/L getting worse also.... yet when you shift down into a more efficient gear to suit the incline and rev it, it uses less fuel/duty cycle due to the resulting less load.. .you could even maintain 6krpm on the lower gear (while not on load) and it had less injector duty cycle & better KM/L than flooring say 4th/5th gear while on load

:thumbsup::thumbsup: good info

u should be changing gears every 20km/h

ie 1st to take off, 2nd change at 40km/h, 3rd change at 60km/h, 4th change at 80km/h, 5th is anything after 80km/h
^^this is usually the best times to change gear for our hondas
and depending, on ur gearing should be bout 3-3.5k rpms

[sretocz]

I usually shift between anywhere between 3-4, 1st like at around 20kmh 2nd 30-40kmh 3rd to 40-60kmh then just cruise in 4th

[steve88]

yep depends on where you are, on a hill you have to go to about 3-4k depending on the steepness. on a flat road i can change at 2-2.5k happily. at any rate, you can feel your car struggle anyway

[krogoth]

im not sure, but the biggest factor for fuel efficiency is how far/deep u press the accelator pedal

the more u press the accellerator pedal, the more the throttle body/butterfly valve opens, lets in more air, therefore more fuel

another way of thinkin about it is.....u can get to 6k rpm in 2 ways

1. slam the accelator all the way to the floor, opens throttle completley, engine hits 6k in a few seconds

2. lightly press on accelator, 1/4 way down, engine takes much longer to get to 6k rpm as u are using much less fuel to get it there

[dc2dc2dc2]

how do u manage to shift @ 1.5rpm seriously.

[krogoth]

lol, yeh i reckon, im always in the 4-6.5k region unless cruising, love to hear the zorst, lol

still get around 450km out of 35L, and its too damn slow to shift lower

[mrwillz]

tai shifts into reverse at 6.5k rpm
thats bad...

[dc2dc2dc2]

nothing beats vtatch in reverse.

[krogoth]

mrwillz needs to wash his car, no more spam, lol

[andiiso]

i used to think shifter lower is more fuel economy, but then if shifting at 1-2k rpm, it feels as if the car is gettin alot of strain put on it AND also that when i used to shift at 3 max i get crappier fuel economy then i do now shifting at 3.5-4k rpm, and plus on inclines etc i wont use 5th gear if going 60 cos like someone bfore said, you can push the accelrator ALLL the way down but there will be no response thus wasting petrol, whereas in 4th you push enuff to get it goin u savin petrol. also shifting too low lugs your motor, dont u feel it sometimes ? shifting too low its hard to get a smooth drive unless ur constantly rev matching while shiftin up and driving normally .. im bad at explaining sorry

also, its not always shifting at lower = fuel economy (what alot of people think including my sister n dad) i think its better said as, shifting at an adequate rpm = fuel economy(depends on car wat RPM it is to be adequate eg, my ek4 shifting at 3-4k is adequate and smooth, but in the my sisters corolla shifting at 3.5+ is like im bout to vtec in my civic minus the power haha and shifting at 2.5-3k is adequate for corolla)

[xenonkuraz]

Another thing I guess I haven't considered is how heavy my right foot is at times.

[blk_shadow]

Another thing I guess I haven't considered is how heavy my right foot is at times.

that explains lol

[1996ek1]

Perhaps its because when u shift at lower RPM, it struggles to accelerate, and will barley move, so you step on it more, using more fuel. Just a thought...

[mrwillz]

how do u manage to shift @ 1.5rpm seriously.

wot top speed do u get?

idle is around 900rpm n u shift 600pm over that.. dang!

wot bout on a hill
i'd like to see u try

[dsp26]

Perhaps its because when u shift at lower RPM, it struggles to accelerate, and will barley move, so you step on it more, using more fuel. Just a thought...

exactly

[NightKids]

Do you guys keep it in 4th while cruising at 80km/h? Because I would always shift to 5th in that situation....

[yourfather]

depends on type of road. usually im in 5th

[andiiso]

im usually in 5th and like yourfather said, depends on what road, sometimes 4th cos im going 80 then up a hill and as a ek4 revs will drop n so will kms in 5th even if im already goin 80, so i mite go 4th in that situation

[SeverAMV]

Perhaps its because when u shift at lower RPM, it struggles to accelerate, and will barley move, so you step on it more, using more fuel. Just a thought...

thats true. you drop out of your car's torque range so you pump in more fuel to counter it. there's an optimum shift point in each gear, you just have to figure it out.

and its not too hard shifting at 1.5krpm, you just need to have good clutch control to ride it out properly.

[dsp26]

thats true. you drop out of your car's torque range so you pump in more fuel to counter it. there's an optimum shift point in each gear, you just have to figure it out.

and its not too hard shifting at 1.5krpm, you just need to have good clutch control to ride it out properly.

half true... again it depends on the load put on the engine... this "optimum shift point" varies on incline/decline thats why there is no set rule... its called common sense.

[bennjamin]

get into a higher gear as the higher gear teh lower RPM's. Works in normal driving conditions but excess load will still result in excess fuel consumption and possible engine damaged.
IE highway driving is say 110 km/h @ say 3500rpm , while city driving is an average 4-5000rpm whatever gears. More fuel used.
Be interesting to know exactly what amount of fuel is used per RPM and depending on throttle and load.

[dsp26]

^^^good point as i have been meaning to bring it up...

with this consult device, when i was engine breaking down a hill in 2nd gear/6krpm no throttle
- injector duty cycle stayed at ~5%-15%
- TPS voltage was low because no throttle
- AFM voltage was low to mid range therefore it wasn't dangerously lean

4th gear with slight incline from about 2.5krpm accelarating
- NO INCREASE in acceleration ability past 50% injector duty cycle and about 60% TPS voltage range
- AFM voltage was constant with acceleration
- L/100KM would get really bad past the point of above TPS/AFM points with no benefit

3rd gear at ~4500krpm (peak torque for this car)
- had obviously better acceleration and not in WOT
- TPS voltage would be lower and not have much throttle and less injector duty cycle yet AFM voltage would increase quicker than the higher gear.

With the above scenario also... once 6krpm was reached.. it was idled ont here while the engine was not on load.. ie the road was flat and:
- TPS was constant
- Injector duty cycle % was lower
- L/100KM was still better than the higher gear struggling on load

[zco]

no gear/rpm combo is better for shifting as it depends on speed vs load.

on flat road or at highway speeds the higher gear/lower rpm combo is better for efficiency.

however in city/hill driving its better to be in a lower gear and revving higher as:
- it reduces load on engine
- quicker to get to speed you want due to gearing

Although this should be common sense, ECU consult hook-up on my previous car backed this up when say in 4th gear/~70km/h on an incline... no matter how much i pressed the accel pedal there was no increase in acceleration despite injector duty cycle increasing and measured KM/L getting worse also.... yet when you shift down into a more efficient gear to suit the incline and rev it, it uses less fuel/duty cycle due to the resulting less load.. .you could even maintain 6krpm on the lower gear (while not on load) and it had less injector duty cycle & better KM/L than flooring say 4th/5th gear while on load
hit the nail on the head :thumbsup:

[dsp26]

my point is, no one here, nor any race rar driver or grandfather who insists he's been driving for 50yrs can tell you the exact optimum gear vs fuel economy ratio unless:
- They know their gear ratios biblically
- They know their powerband for each gear biblically
- They know their sensor reading behaviours biblically
- And engine load effects of *degree incline/decline

The best measure is common sense with the 'feel' of your right foot/accel pedal versus car/engine behavious with load.

Even an ECU consult cannot be taken biblically for fuel economy as the L/100KM measure is taken per second based on TPS/AFM or MAP/O2 voltages affecting injector duty cycle... for example the current BMW 3/5 series that has the analogue fuel usage meter.

The more accurate ones are the ones that take the epr second reading and take about 10,000 of them and average it out....

[bennjamin]

yup yup. Great discussion here.

To find what is the best driving style for your car (economy wise), you drive it and find out :)