r u using more fuel at 3000 rpm in 4th gear at full throttle or are u using more fuel at 6200rpm in 1st gear at half throttle? asking cause i duno if the fuel consumtion is determined by the engine speed or by the throttle(cause doesnt the throttle body just open up the air flow and not the fuel line?). flamers welcome, but please provide answer..... thnx. why is this such a great site? (searched)

 

You would use more fuel at full throttle in 4th.

 

why please?.......... i have an idea... can someone put it into words? thnx

 

In 1st gear, there is less load on the engine because the gearing is doing the work, in 4th gear, which I think is a 1:1 ratio(or close to it) on most manual Hondas, there is a higher load on the engine.

Think of gas usage as doing work, the more work you get done, the more gas you will use. Time is also a factor, the quicker you want the work done(accelerating the car) the more gas it will take as opposed to doing the same work over a longer period of time where you would use the same amount of gas to do more work, there's no free lunch.

I've gone crosseyed

 

so basically the more opened the throttle is, the more fuel will be consumed to keep the fuel to air ratio?

 

well I am pretty sure that you are burning more fuel, the more the throttle goes down, hence why the RPM's go up, cuz you are feeding more fuel and air...

 

I think it normally works out better (for fuel economy) to be at lower RPM & more-open throttle. Thermodynamic efficiency should be better with less manifold vacuum, for engines with compression ratio above 9:1 or so. Engines with lower compression ratios have better efficiency with higher manifold vacuum. (But who makes engines with 7:1 anyway...)

A closed throttle represents a BIG loss of efficiency. So you're better off flooring it & shifting at 1800 RPM. That's strictly a generalization for fuel economy, so don't flame me about it being unhealthy for the engine...

 

/\ sry to sound like a noob, but r u serious about the flooring and shifting at 1800? but when u drive ur daily driver car (strictly city driving)...... do u constantly open the throttle a little bit (enough to keep the momentum going) and coast to stops to get higher mpg. or do u tap the pedal when u feel like ur slowing down to get back to speed then coast to stops?
im asking cause my 01' accord lx, l4(f23a4)->(sohc vtec), auto tranny with i/e suks in mpg with 17 in the city with average joe driving....... and i wanna learn more about how engines werk. thnx

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pooMan &raquo;</TD></TR><TR><TD CLASS="quote">so basically the more opened the throttle is, the more fuel will be consumed to keep the fuel to air ratio?</TD></TR></TABLE>

This is correct.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pooMan &raquo;</TD></TR><TR><TD CLASS="quote">i duno if the fuel consumtion is determined by the engine speed or by the throttle(cause doesnt the throttle body just open up the air flow and not the fuel line?)</TD></TR></TABLE>

The amount of fuel injected depends on both the engine speed and manifold pressure, which reflects the amount of air entering the engine. The throttle controls the pressure in the manifold, so more throttle = more pressure, speaking in absolute terms.

JimBlake (as usual) is correct, the highest theoretical fuel efficiency comes from wide open throttle at low RPM, as this reduces pumping losses against any manifold vacuum. It's also the reason the BMW Valvetronic system is more efficent; there's no throttle for the engine to "fight".

 

/\ good stuff! /\ so just to clarify even more.... about engine speed and opening the throttle..... would u be using more gas having it floored in 1st gear at 6200rpm or floored in 5th gear at 1500rpm. from what u guys have said, 5th gear at 1500rpm should take in less gas since the ecu detects lower engine speed. i hope im right. thnx for clarifying.... (am i correct?)

 

Once again you are correct. In general, given the same manifold pressure, the engine will consume less fuel at lower RPM.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pooMan &raquo;</TD></TR><TR><TD CLASS="quote">... would u be using more gas having it floored in 1st gear at 6200rpm or floored in 5th gear at 1500rpm...</TD></TR></TABLE>Floored in 1st at 6200 would use way more gas than floored in 5th at 1500.

Here's a better comparison.

Fifth gear at 1700 rpm, climbing up a hill where you can keep a constant speed with the gas nearly floored.

Third gear climbing the same hill, same constant road-speed, whatever RPM that is. Only press the gas enough to climb at the same constant speed without accelerating.

Using 5th gear at lower rpm almost floored will use less gas. The reason it's a fair comparison is the engine is doing the same amount of external work to push the car up the hill. Your comparison that I quoted above isn't fair because the acceleration will be much different between those 2 cases.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pooMan &raquo;</TD></TR><TR><TD CLASS="quote">... r u serious about the flooring and shifting at 1800?</TD></TR></TABLE>I'm serious about it being better for fuel economy. But it's not the best thing for engine lifespan. It's also not too swift for being prepared to move around in traffic, so you gotta use some common sense.

I've done that, but maybe not as extreme as my example. If I don't feel like impressing the people in the next car over, I'll put the gas pedal maybe 3/4 down or more, & shift before 2000 RPM. Once you know your own engine you'll learn how early you can shift without getting stupidly low RPM in the next gear. It can't be too bad since I've done this for years.

Can't do that with an automatic, because you can't prevent it from holding the lower gear & racing away in a big cloud of used gasoline. You have to reprogram the tranny to behave like that, but you wouldn't want it all the time. (I don't like automatics...)

For gas mileage I've gotten the habit of anticipating what's going on way ahead of me. See a green light 1/2 mile away? You KNOW it'll be red by the time you get there, so leave it in gear & take your foot off the gas. The best way to get better fuel economy is to get better control over the testosterone levels...