Coasting vs. Engine Braking

[caveatipse]

ok thanks.

[skewbe]

Well, it isn't as simple as JanGeo said. If you are engine braking (or any braking) you are bleeding off speed that took gas to make.

I suggest you look at installing a fuel injection kill switch and understand the pros and cons of pulse and glide ( EOC ) if you really want to maximize your mpg in your stickshift Yaris.

[caveatipse]

Originally Posted by skewbe

Well, it isn't as simple as JanGeo said. If you are engine braking (or any braking) you are bleeding off speed that took gas to make.

I suggest you look at installing a fuel injection kill switch and understand the pros and cons of pulse and glide ( EOC ) if you really want to maximize your mpg in your stickshift Yaris.

But if you are slowing down at all, you are bleeding off speed it took gas to make. If all other things are equal, if engine braking actually stops gas from flowing, and coasting keeps it flowing, how can it not be that engine braking saves more gas, all other things being equal??

[skewbe]

The most fuel efficient mode of operation for a gas powered vehicle that I know of:
http://metrompg.com/posts/xfi-pulse-and-glide.htm

The point is to avoid any sort of braking and to accelerate just enough to coast to the next stop. If you are engine braking you will have to accelerate more to cover the same distance, if you are just coasting you will travel farther after you get off the gas. If you can live with killing the injectors while coasting, even better.

We are trying to save gas here, right? Or are we here to debate hypotheticals with little return?

[caveatipse]

Originally Posted by skewbe

The most fuel efficient mode of operation for a gas powered vehicle that I know of:
http://metrompg.com/posts/xfi-pulse-and-glide.htm

The point is to avoid any sort of braking and to accelerate just enough to coast to the next stop. If you are engine braking you will have to accelerate more to cover the same distance, if you are just coasting you will travel farther after you get off the gas. If you can live with killing the injectors while coasting, even better.

We are trying to save gas here, right? Or are we here to debate hypotheticals with little return?

lol no I just do not understand and I want to understand. If I engine brake, why will I have to accelerate more? If I get off the interstate on an off ramp, for example, and I am going to have to come to a complete stop anyway, why not do so in a manner that completely shuts off fuel flow, rather than a manner that leaves some fuel flowing?

[skewbe]

the kill switch takes care of the fuel flow and allows you to cover more ground while using zero fuel. If traffic is light (or you just don't feel like being pushed) you can shut off the engine sooner and coast much farther than you can in gear.

If you are a fan of pool, you may understand that some shots require you to hit the ball just hard enough that it stops exactly where you want it. This is the same concept, you try and kill the engine at just the right speed and distance from the next obstruction that you roll to a stop where you meant to. Takes practice and some brakes are the norm (if I never use the brakes over 20mph I'm doing ok). But in that manner you do not over-accelerate and then throw that energy away in braking.

[caveatipse]

Argh lol but that is not what I am talking about. My Yaris shuts off the fuel flow completely under engine braking. So it is only logical that, if I have to slow down to a stop anyway, doing so with NO fuel is better than with a LITTLE fuel. How am I wrong? (pulls out own hair)

[skewbe]

What is your goal? Does it relate to this hypothetical question in a significant way?

[caveatipse]

Originally Posted by skewbe

What is your goal? Does it relate to this hypothetical question in a significant way?

lol my goal is to use the least amount of fuel possible when coming to a stop where I HAVE to stop.

[skewbe]

Originally Posted by caveatipse

lol my goal is to use the least amount of fuel possible when coming to a stop where I HAVE to stop.

Ok, then still look into pulse and glide and EOC . If you kill the engine with a kill switch it won't be burning any fuel, and you can get off the gas pedal sooner (I assume you can anticipate most of the stops) if you put in the clutch as your speed will not bleed off so fast as it would if you left it in gear. You may find that you can kill the engine way ahead of the off ramp and coast for miles with no fuel.

How much speed you carry into that stop that you HAVE to stop at is going to be the main determinant in how much energy you will lose at that stop by braking.

If it makes you feel better, then you are correct about the hypothetical situation where you could not anticipate the stop (or did not change wasteful driving habits) and managed to trick the engine into turning off the fuel for some portion of the deceleration by engine braking.