Fuel Efficiency Compilation [long read]

[mondojackal]

It should be noted that higher throttle/lower engine speed use takes better advantage of throttle angle to increase efficiency. Any conventional internal combustion engine will be most efficient at WOT. However, a caveat to that is that, while it's most efficient at any given point, it does not mean that you're automatically getting great fuel mileage.

Most efficient can be narrowed down to "most power given for the amount of fuel used" in a given situation. You get the most power down low with larger throttle inputs, but keeping the revs low will allow you to not uselessly waste fuel when the next gear can be selected and engine speed reduced.

[Nurega]

It should be noted that higher throttle/lower engine speed use takes better advantage of throttle angle to increase efficiency. Any conventional internal combustion engine will be most efficient at WOT. However, a caveat to that is that, while it's most efficient at any given point, it does not mean that you're automatically getting great fuel mileage.

Most efficient can be narrowed down to "most power given for the amount of fuel used" in a given situation. You get the most power down low with larger throttle inputs, but keeping the revs low will allow you to not uselessly waste fuel when the next gear can be selected and engine speed reduced.

You are correct. This is one of the reasons why Diesel engines are more efficient than their gasoline counterparts; the throttles on a Diesel stay fully open regardless of how far your accelerator is pressed. I'll add something to the main thread about this.

In my Acura, I find that keeping the revs around 1500 provides optimal fuel efficiency in the city. It's unfortunately difficult to use this WOT principle to our advantage in gasoline engines, but keeping the revs low still has a fair impact.

[8ball]

Really good thread enjoyed it. I wants 36mph too lol.

[8ball]

Really good thread enjoyed it. I wants 36mph too lol.

I just did 35mpg

with me (270lbs)
and a set of prelude alloys with tires in the trunk
and a full tank of gas
doing 80mph the whole way
some but not much (50miles) of city driving
and quite a "FEW" WOT burst
on 40psi 14 inche steelies


Crazy shit what a tune up and alignment can do.

[Stormtrooper]

b. Coast. When you let your foot of the throttle when the car is in gear, ZERO FUEL is used.

If the engine is running, fuel is being burned.

EDIT: But otherwise, great write-up!

[Nurega]

If the engine is running, fuel is being burned.

EDIT: But otherwise, great write-up!

Actually, this isn't true.

Let me propose an example. You are driving at 40mph, in 5th gear. You switch the ignition key off while moving. I think you'll agree that there is currently no fuel flow to the engine at this point, but the engine is technically still moving.

Similarly, when you let off the throttle, and the vehicle is moving and in gear, the fuel flow is stopped. Only when the engine is idling (not in gear) does the idle air-control valve (IACV) come into play, thus allowing the engine to stay on by opening the intake.

[Stormtrooper]

So you're saying that with the engine on, the car moving and in gear, if you release the accelerator pedal, the throttle body will be completely shut? No fuel is injected? No combustion is taking place?
Is the engine still rotating at this point? Pistons, valves, etc.

[reklipz]

Similarly, when you let off the throttle, and the vehicle is moving and in gear, the fuel flow is stopped. Only when the engine is idling (not in gear) does the idle air-control valve (IACV) come into play, thus allowing the engine to stay on by opening the intake.

I've torn apart and rebuilt the [five speed manual] transmission on my CB7 (F22A1 w/ H2A5). There is no sensor telling the ECU what gear the car is in, except for reverse. I suppose it's possible that the ECU might know the gear ratios of the transmission, and given the engine RPM and the vehicle speed it could determine what gear you were in (assuming the clutch was all the way depressed, but that's probably valid; also, it could probably tell neutral as well, as idle is usually lower than anything you'll ever see in gear (5th gear at 30 mph gives... below idle? probably going to stall the engine, so this is probably valid to assume it will never happen)).

I know that people change the transmission without ever touching the ECU, and I think people generally assume that a PT3 is a PT3 is a PT3, and a PT6 is a PT6 is a PT6, regardless of the transmission that was on the engine. If these are true, then the ECU cannot calculate the gear, unless the transmissions installed with a certain ECU is always the same. Does anyone know?

If the ECU doesn't know what gear you're in, then it's reasonable to believe it will always give at least the "idle amount" of fuel. It's possible it will give more (since it can know that it is at least "in gear", and might do something different then). I think someone who is familiar with ECU tuning and the fuel map can chime in on this topic.

[mtnbikaah]

When slowing down in gear (5spd) the ECU goes into "Deceleration/Fuel Cut-Off" mode, therefore using no fuel.

[reklipz]

When slowing down in gear (5spd) the ECU goes into "Deceleration/Fuel Cut-Off" mode, therefore using no fuel.

Awesome. Wikipedia backs up your claim, so long as the CB7 is a "later-model vehicle with a fuel-injection engine", which is likely the case. This page is basically this thread times 10: http://en.wikipedia.org/wiki/Fuel_ec...zing_behaviors

This section sounds awesome: http://en.wikipedia.org/wiki/Fuel_ec...e_and_glide.22

[BIGRICH]

When slowing down in gear (5spd) the ECU goes into "Deceleration/Fuel Cut-Off" mode, therefore using no fuel.

thats cool and all.....but, what about auto trans?

[reklipz]

thats cool and all.....but, what about auto trans?

.

For coasting in gear, a later-model vehicle with a fuel-injected engine will realize more gains from the burn and coast technique than older carbureted engines because the engine control units in most fuel-injected engines will cut fuel to the engine when the car is in gear, the throttle is closed and the engine is running faster than idle speed. This is sometimes referred to as "deceleration fuel cut off". This will often engage while a car is coasting down a hill and is common in both automatic and manual transmission vehicles, although the particular engine speeds at which it will engage vary.

[BIGRICH]

.

cool story.....my auto loses speed while in gear going downhill. if i shift to neutral the sensor you speak of isnt working.....how do you coast and use zero fuel then?

[mtnbikaah]

Of course you are going to slow down. It's called compression braking, IIRC.

and you coast by taking your foot off of the gas. and that's it!

[BIGRICH]

Of course you are going to slow down. It's called compression braking, IIRC.

and you coast by taking your foot off of the gas. and that's it!

coasting and slowing are two different things, bruh. my only point is, you cant coast and maintain, much less gain any speed when in drive in an auto car.....therefore the coasting with "zero fuel use" comment is not valid for an auto car.....period.