Sounds like skip-shifting to me

 

And throttle position directly controls how open (or closed) the throttle body is, thus controlling airflow into the cylinders. Case in point: If Im at 7,000 rpm and completely let off the throttle, how much fuel am I consuming? I agree, if I do the same test at 2,000 rpm I'd be using less, not arguing that. My point is that in real-life applications, throttle settings are never the same. You're always having to apply more throttle to maintain speed on an incline, and can reduce throttle to maintain speed at during a decline. Try this one for me, leave it in 5th @ 2,500rpm while trying to climb a grade, and put it in 3rd and do the same. You're not going to be able to really test this unless you having real time fuel consumption monitoring, which a lot of newer cars have, but unfortunately the S doesn't.

 

Freaking THANK YOU.

It should be obvious really just by using anecdotal evidence. They keep coming out with 8 and 9 speed autos with super-long highway gears for increased efficiency. Cars with huge, thirsty engines like Corvettes and Vipers have insanely long 6th gears, so long that top speed is achieved in 5th because even with 500lb/ft+, they can't pull such a long gear toward 200mph. CVTs like the one in my dad's '13 Accord keep revs very low (below 1,500rpm most of the time) to achieve better gas mileage. Yet somehow people believe that you want to be in a lower gear to save gas? In what world does that make sense?

Higher revs = more friction = more energy wasted. Less throttle at a higher rpm to maintain a given speed = more pumping losses than using more throttle at a lower rpm to maintain the same speed. It's been proven time and time again, I don't know why people are trying to argue otherwise.
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Let's say you shift at 4,500rpm in the city (so, much lower average rpm total) and cruise at 4,500rpm on the highway, why your city mpg lower?


thats because they have low end torque. If it's been proven time and time again, can you post a few links for us? If I go up a hill and I have to increase throttle to maintain speed, rpms dont change at all, but my fuel consumption does. You guys are talking like we drive on completely flat surfaces with zero elevation changes. Im not going to drive around town in 6th is what im getting at, just to accelerate at 1,500rpm is going to take a lot more gas than to accelerate to x mph at 4,000 given the power efficiency of the motor.

http://uk.answers.yahoo.com/question...5073519AAq5SOa
http://www.physicsforums.com/showthread.php?t=255882

Lastly, you have to open the throttle to bring the rpms up, just sayin

 

We're talking about cruising in town on flat ground, not hauling up a hill when you NEED power.

You ask for evidence, so I'll point you to my friend's auto engineering class (below) where it compares optimal RPM range for a given required power output, and how Honda autos shift.

At Higher RPM you win a little from slightly more torque but lose pumping losses/friction, to the point where 2500 RPM almost always beats 4000 RPM while cruising.

Also the giant V8's don't directly apply to Hondas, but still a less torquey motor just moves your optimum RPM up slightly, just not all the way to 4000.

My Prelude's H22 made 200hp @ 7K and 156lb-ft at 5.3K, typical Honda. I shifted around 2.5-3K in "normal" driving and cruised at 1.8-2.5K comfortably. My friend had the automatic version and would cruise at 2K all the time. Ditto driving my old Accord with F22A1 (125hp@5.2K, 137lb-ft @ 4K), the auto shifted up at 2.5K. Would always be in top gear at 40MPH. The engineers know the motor doesn't have great torque, yet decide not to hold lower gears in the interest of gas. What you really have to look at is the torque curve, and if you can get to the "fat part" by revving a bit higher it's worth it.




And city MPG is bad due to constant braking and acceleration. If you just hit the cruise at 45MPH sixth gear and had no lights, you'd get fantastic mileage. Probably better than at 60MPH.

Also when you let off the throttle at 7K and 2K you should both be using no gas at all due to deleration fuel cutoff. If you coast down in fifth from like 30 you can actually feel the "idle" kick back in near 1000 and the computer feed in more fuel to keep the motor alive.

 

This is not a debate about steady state cruising. Where the lowest rpm would yeild the best mpg, because minimal force is required to keep the car in motion. We are talking accel from a stop or slow speed to get up to normal crusing speed. I can tell you that trying to shift less than 2-2500 rpm is using MORE FUEL than if you drive the s2000 where the engine is most efficent (higher rpm).

How is this possible? But less rpm means less fuel is used right? Yes, less fuel is used at lower rpm. HOWEVER. You kinda forget how long it takes you to accelerate when shifting at 2-2500 rpm. It will take forever to get up to speed. You'll have mopeds and blind old people passing you at stop lights. So here you are in your s2000 and it takes you 30 seconds to get to 50mph. Because the s2000 makes so little power and is highly inefficent at that rpm it is actually wasting fuel and not going anywhere and you are doing this for a long time. The engine is almost being lugged at that rpm. This means the fuel energy is not being efficenty translated into power.

It is better to drive accelerate lightly and rev the engine out to 4k rpm for your shifts, this gets the engine in its efficency range and allows to drive safely as well. The key is to use a low throttle position.

I did a controlled test on this very subject, and drove an entire tank of gas shifting at 2-2500rpm. It was a nightmare in traffic. I found I had better mpg driving with higher rpm and was able to do so safely.


for the record. When I drive the S2000 I nearly always shift at 4.5-5k rpms when driving normally and not trying to do above mpg tests. The engine is happiest in that shift range and the shifts are much smoother.

 

No disagreement there, but that's not real life Let's take a sec and re-read the OP.

The chart is a good representation. And I agree with those sentiments. I just find the varying consumption lines interesting. Looks like if you make low power at low rpm your fuel economy is going to suffer a bit.

 

This topic is fairly complicated. As a whole, I agree with what ZDan has written and disagree with RedCelica, in particular the first part of:
Gas is consumed based on the fuel injectors and the duty cycle. This is determined by the ECU using multiple inputs.

In general, operating at smaller throttle openings (e.g. shorter gear for the same level of power) will be less efficient because of increased pumping losses. Operating at higher engine speeds (e.g. shorter gear for the same vehicle speed) will be less efficient due to increased frictional effects.

As to whether it's better to shift at 2,500 rpm or 4,500 rpm I'm not certain because the level of acceleration wasn't well defined and fuel economy isn't the only consideration. However, from the "cruising" part part at 25000 vs 4500 rpm, 4500 rpm would likely be less efficient.

 

^^^I agree, but also consider that the ECU is going to tell those parts what to do based off the primary input of manifold vacuum reading.

I think my usage of the word "cruising" here is confusing folks. I simply mean around town, not a constant rate of speed, but of acceleration.

 

Yes. But the airflow and fuel required are *also* a function of rpm. That's what I meant when I said that the throttle position doesn't *directly* control rate of fuel consumption. It directly controls the throttle butterfly. Fuel is supplied commensurate with the air going into the engine. For a given throttle position, the engine will take in a lot more air (and produce a lot more power) at 7000rpm than it does at 2000rpm, and will thus require a lot more fuel at the same throttle position.

At the same *power* setting, of course the throttle will be a lot more open at 2000rpm than at 7000rpm. But for cruise power levels, fuel consumption will be a lot less at with more open throttle at 2000rpm than with a more closed throttle at 7000.

 

Yes. But the airflow and fuel required are *also* a function of rpm. That's what I meant when I said that the throttle position doesn't *directly* control rate of fuel consumption. It directly controls the throttle butterfly. Fuel is supplied commensurate with the air going into the engine. For a given throttle position, the engine will take in a lot more air (and produce a lot more power) at 7000rpm than it does at 2000rpm, and will thus require a lot more fuel at the same throttle position.

At the same *power* setting, of course the throttle will be a lot more open at 2000rpm than at 7000rpm. But for cruise power levels, fuel consumption will be a lot less at with more open throttle at 2000rpm than with a more closed throttle at 7000.
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Right, because the motor's pulling (more manifold vacuum) a lot more air @ 7k @ 50% throttle than 2k @ 50% throttle, not arguing that.