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For a flat road with a maximum speed limit of 60 kph, which would be better for a 2.4L 4CYL i-VTEC gasoline engine (K24A4 rated at 160HP @ 5500 rpm, 218Nm @ 4500 rpm):

  • 3rd gear at 2500 rpm

  • 4th gear at 1100 rpm

Will there be a difference in fuel consumption or would one be better for the engine, transmission, etc?

closed as primarily opinion-based by Solar Mike, Chenmunka, Nick C, Steve Matthews, Rory Alsop Jul 27 '17 at 12:24

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    This is about driving style and is not clear : driving on the flat, uphill, downhill etc What engine - large diesels can produce most of their torque at low revs... – Solar Mike Jul 27 '17 at 6:54
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I assume we're talking about a car with a normal rpm range here? If so.. And the vehicle had a max rpm of about 6000rpm.. Then It would likely be more fuel efficient at 1100rpm. However.. At 1100rpm an ordinary engine is only a few rpms above tickover, so smoothness and driver/passenger comfort must come into account here, especially as even slight inclines in the roads surface would lower the rpm further taking the engine towards a stalling condition, this then would increase vibration etc further so more throttle would be required, unless you then changed down a gear anyway.

A vehicles fuel efficiency monitor will likely tell you at 60kph to change up a gear from 3rd to 4th for economy, however a vehicles fuel economy system doesn't take practicality or feasibility into account.

So IMHO I would say that perhaps 2500rpm would be more appropriate here, but not necessarily more economical. Plus at 2500rpm you are more in control of the vehicle, in the sense that it wouldn't just be labouring its way along the road with only poor acceleration and engine braking available to you.

  • Most cars seem to cruise at 70mph at approx 2000 rpm... – Solar Mike Jul 27 '17 at 7:11
  • @SolarMike yes but the original question stated 4th gear 2500rpm so the answer here is correct to reference that, regardless of what most cars do. My diesel engined car sits at 70mph at 1800rpmin 6th gear, my petrol car sat at 70mph at 2750rpm in 5th gear (no 6th) – Mauro Jul 27 '17 at 7:17
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    @Mauro this is one of the reasons why this type of question is off-topic : gear ratios have changed over the years and so have max and cruising speeds.... – Solar Mike Jul 27 '17 at 8:14
  • @Mauro and if you read the question in detail 4th gear is 1100rpm and 3rd is 2500..... – Solar Mike Jul 27 '17 at 10:28
  • yep - sorry got it the wrong way around. – Mauro Jul 27 '17 at 12:30

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