Fuel Saving Techniques

[LxAcc510]

Copied this from another forum for the M3.

Fuel saving techniques:

1) If possible, never use the brakes. Any time you're in gear and not on the gas pedal you are getting virtually infinite mpg. To that end:
-never tailgate-- it forces you to use the brake pedal. No amount of "drafting" is going to make up for that
-the moment you see a red light, get off the gas and coast. You're not going to get to the destination faster by getting to the red light faster
-DO NOT TAKE THE CAR OUT OF GEAR WHEN YOU'RE SLOWING DOWN. Leave it in gear until your RPMs are around 1400, then put it in neutral. You're not using ANY gas at all if you're off the gas and in gear

2) Prepare the car properly
-Low tires pressures will cost you fuel economy. I run 36psi (cold)
- keep your car as light as possible- don't keep your crap in it.
- a bad alignment can also destroy fuel economy-- especially too much toe!

3) Mods can hurt fuel economy too
- gears mean your using more fuel at any speed
-wider tires are worse as they create more rolling resistance
-many power mods lose mpg
-any software that increases throttle sensitivity is going to make you more likely to be on the gas more
-exhaust are likely going to make you want to be in the wrong gear-- the drone zone is pretty optimal for fuel economy

4) General techniques:
-as much as possible accelerate on the downhill and coast on the uphill. Be willing to lose some speed going up hill, but no so much as to require a downshift
- use as little throttle as possible. WOT uses much more gas then edging up to speed
- higher gears are always better (but don't lug the engine). 6th gear pretty much all the time on the highway
- never use the brakes if you can help it!
-when accelerating, get into the next gear as soon as you can without lugging the engine. By 40mph you can easily be in 4th gear.
- don't use cruise control, so long as you're actually able to do the above. I got 3mpg better on the highway with my foot than with cruise control, and that didn't even include ANY traffic, traffic lights, etc-- just wide open straight road that I had to myself)

5) Don't skimp on the octane: You will get lower MPG with lower octane gas. High octane gas pays for itself, don't skimp!

http://www.m3forum.net/m3forum/showthread.php?t=216328




--What do you guys think?

[84Accord]

Copied this from another forum for the M3.

Fuel saving techniques:


-DO NOT TAKE THE CAR OUT OF GEAR WHEN YOU'RE SLOWING DOWN. Leave it in gear until your RPMs are around 1400, then put it in neutral. You're not using ANY gas at all if you're off the gas and in gear


http://www.m3forum.net/m3forum/showthread.php?t=216328




--What do you guys think?

sounds good except that. if you put it in neutral. rpms drop to 1k or less. so therefore loosing less gas than if you were letting the engine slow you down...

[Vanilla Sky]

If your car is still in gear, you're using no fuel. This is from an M3 forum. Those cars cut fuel and spark when coasting in gear. Letting off the clutch or going to nuetral makes the car idle, which uses gas.

['89AccordLX(Rus)]

Carburated engines will continue to receive fuel during the coasting stage because the carburetor works based off of engine vacuum (and the idle circuit injects gas below the throttle butterfly on the 3G keihin carbs), so that part is not going to be effective. What's more, some engine control systems will cut the fuel injection off while coasting, BUT may re-enable it in order to maintain proper temperatures in the catalytic converter(s). This would be necessary during periods of extended coasting where the engine is not receiving fuel for a long time and thus exhaust temperature drops. As for the octane rating point, that is likely true for an engine that is originally designed to use higher octane fuel. These engines are typically high compression and thus need the higher octane rating to avoid detonation/preignition. If a low octane fuel is used and the engine control unit receives a preignition notification from the knock sensors, it will add more fuel to richen the mixture (a mixture more rich in fuel doesn't auto-ignite as easily), and therefore fuel economy will be decreased. Again, this would be of no interest to the 3G owners because the A20 engines are not high compression and I have never heard of a knock sensor on a A20 engine either. This all isn't gospel, but rather what I've learned from reading and working with engines and their control systems. Just my $.02

[Accordtheory]

Copied this from another forum for the M3.

Fuel saving techniques:

-wider tires are worse as they create more rolling resistance

I doubt this very much. Wider tires do not deflect as much with the vehicle weight. Imagine a bicycle tire on a car, how much would it deflect. The more deflection, the less round the tire is, the more rolling resistance. Sure you could inflate the narrower tire more, but there is an ideal size for everything. The oem accord size is probably too small, for no other reason than to save $. I highly doubt you'd see any decrease in fuel economy from properly inflated 205/40/17s. (That's what I have.)

--when accelerating, get into the next gear as soon as you can without lugging the engine. By 40mph you can easily be in 4th gear.

Maybe. You'd have to look at a curve of bsfc vs rpm, for the torque required to achieve the desired rate of acceleration, and then figure it out. An engine is not always most efficient at generating a certain hp number at the lowest rpm that it can do it. There is a certain optimal rpm/manifold press for a certain hp demand. (Drive by wire attempts to more closely attain this)

I don't use cruise control, so long as you're actually able to do the above. I got 3mpg better on the highway with my foot than with cruise control, and that didn't even include ANY traffic, traffic lights, etc-- just wide open straight road that I had to myself)

How..? Your cruise control must be getting on and off the gas a lot more than your foot.

5) Don't skimp on the octane: You will get lower MPG with lower octane gas. High octane gas pays for itself, don't skimp!
Well, this is blatantly untrue. Octane doesn't have anything to do with btu content. Btu content is the amount of energy available in each gallon, it is what determines the fuel economy. For example, when e85 came out, there were idiots complaining about how it's a rip off, they should be getting better mpg since it's rated at 105 octane..well, it has about 30% less energy per gallon..so you get about 30% less economy..and it should cost about 30% less.
And as far as the idea of knock enrichment, most ecus don't add fuel, they take away timing, and this is irrelevant for part throttle anyway. You're not going to hit the knock threshold with 87 octane cruising if your car was "designed" for 91. You just might have slightly reduced maximum power and efficiency at maximum power.


--What do you guys think?

[cygnus x-1]

Heh! I was thinking some of the same things.

Unless you go completely off the wall with tire width, rolling resistance I don't think will make much difference *assuming proper inflation*. Inflation pressure will be more critical than tire width. Although wider tires will weight a little more, so... <shrug>

The issue with cruise control is that it can be kinda spastic sometimes. At least the one in my truck is (only vehicle with cruise). If it gets even remotely hilly it always wants to unlock the torque convertor, which means lots of power gets wasted heating up transmission fluid. On a manual trans it might not be so bad. My truck is also underpowered so that probably doesn't help.

RPM is the most interesting. One of the gauges on the Megasquirt gauge panel (when plugged into a computer) is injector pulsewidth. This gives you pretty much a direct indication of how much fuel is going into the engine. It's interesting to watch it as you're driving. You would think that higher RPMs would mean a longer pulsewidth and more fuel, but it's not always so. One of these days I should try cruising at the same speed in different gears and see what the PW does.

I suppose theoretically you could get slightly better mileage with higher octane fuel if the ECU adjusts timing advance for knock. But it seems extremely unlikely that it would make enough of a difference to offset the increased cost of higher octane fuel.

C|

[cygnus x-1]

For the extreme in driving for better fuel mileage, check out hypermiling.

http://www.hypermiling.com/

C|

[Tdurr]

best way to save gas is to ride in the slow lane, shift under 3k, and coast when u see that light way up there turn red. thats wut i do and my modded car still gets like 30something.
~TDR

[LxAcc510]

Carburated engines will continue to receive fuel during the coasting stage because the carburetor works based off of engine vacuum (and the idle circuit injects gas below the throttle butterfly on the 3G keihin carbs), so that part is not going to be effective. What's more, some engine control systems will cut the fuel injection off while coasting, BUT may re-enable it in order to maintain proper temperatures in the catalytic converter(s). This would be necessary during periods of extended coasting where the engine is not receiving fuel for a long time and thus exhaust temperature drops. As for the octane rating point, that is likely true for an engine that is originally designed to use higher octane fuel. These engines are typically high compression and thus need the higher octane rating to avoid detonation/preignition. If a low octane fuel is used and the engine control unit receives a preignition notification from the knock sensors, it will add more fuel to richen the mixture (a mixture more rich in fuel doesn't auto-ignite as easily), and therefore fuel economy will be decreased. Again, this would be of no interest to the 3G owners because the A20 engines are not high compression and I have never heard of a knock sensor on a A20 engine either. This all isn't gospel, but rather what I've learned from reading and working with engines and their control systems. Just my $.02

lol jk. that was just the first smiley i saw.





Great input. I dont know shit about carb'd engines. How do you know all this?

[cygnus x-1]

As for the octane rating point, that is likely true for an engine that is originally designed to use higher octane fuel. These engines are typically high compression and thus need the higher octane rating to avoid detonation/preignition. If a low octane fuel is used and the engine control unit receives a preignition notification from the knock sensors, it will add more fuel to richen the mixture (a mixture more rich in fuel doesn't auto-ignite as easily), and therefore fuel economy will be decreased. Again, this would be of no interest to the 3G owners because the A20 engines are not high compression and I have never heard of a knock sensor on a A20 engine either. This all isn't gospel, but rather what I've learned from reading and working with engines and their control systems. Just my $.02

At first I thought this didn't sound right, but now I wonder. I've heard that on many Nissan VG33 type engines the knock sensors commonly fail, and gas mileage goes down the tubes. I had always assumed that these engines reduced the timing to avoid detonation, but if they added fuel instead (or in addition to) that would explain the mileage drop.

C|

[gp02a0083]

noticed i got my gas milage back after my car threw a code 12, replaced almost everything in the black mystery box, now im sitting with about 160 miles on the trip meter at 3/4 a tank of gas from full

[Accordtheory]

RPM is the most interesting. One of the gauges on the Megasquirt gauge panel (when plugged into a computer) is injector pulsewidth. This gives you pretty much a direct indication of how much fuel is going into the engine. It's interesting to watch it as you're driving. You would think that higher RPMs would mean a longer pulsewidth and more fuel, but it's not always so. One of these days I should try cruising at the same speed in different gears and see what the PW does.


Well, the pulsewidth will vary to match the engine's manifold press and VE at that rpm, but I guess if you can calculate the total fuel going into the motor vs your speed/distance..

The hp required vs bsfc is a pretty complex thing. I'd say for most large engines, they most efficiently generate the power required for cruising at a very low rpm. Like 1500rpm on the open road. But it's a little different for a smaller motor, while it might be able to generate the power required at that rpm, it would actually use more fuel to do so than it would at say, 3000rpm. You're talking about pulsewidth, but that's only half of it, the other half is how much energy the engine is able to generate from that pulsewidth. That's what a brake specific fuel consumption graph is, basically curves of different amounts of fuel burned at different rpms to generate certain amounts of power. I think you hit the nail on the head in principle about cruising in different gears to experiment, but I suspect that in reality, the rpm difference between the gears is too much. I think a change in final drive ratio would be a better experiment.
I really wonder about the gearing the oems put in some cars. Mpg is more and more important these days, but doesn't even the new rsx cruise at around 4k rpm? I highly doubt that is anywhere near the optimal point in that motor's bsfc curve for generating the power required at that speed. And that's a 6 speed too, wtf, why isn't the last gear a little higher? I guess they don't want you to have to downshift to go up hills..
And I'm not even going to get into the s2000, wtf. I've heard the new corvettes get better mpg, at least on the highway, and I believe it.
Obviously the best way to do this would be to use an infinitely variable transmission, so you'd always be able to keep the motor in it's most efficient rpm/manifold press for whatever hp requirement encountered, but unfortunately, it's not like you can just swap one of those in..

I suppose theoretically you could get slightly better mileage with higher octane fuel if the ECU adjusts timing advance for knock. But it seems extremely unlikely that it would make enough of a difference to offset the increased cost of higher octane fuel.

The knock retard only lasts a few seconds, and the motor would only knock under high load, if at all, so I don't see how this would affect fuel economy..
I'm also pretty sure there is no ecu programmed to add fuel as a function of feedback from the knock sensor..
C|

[Accordtheory]

If it gets even remotely hilly it always wants to unlock the torque convertor, which means lots of power gets wasted heating up transmission fluid. C|

I have observed this too, although not as a function of the cruise control. I have driven a vehicle that got better mileage going up hills at 90mph than it does at 65-70, the reason being it would unlock the torque converter at the lower speed to keep the motor in it's powerband, and start to spool the turbo against the converter the whole way up the hill, vs keeping it locked at the higher speed. The torque converter wastes more fuel than the increase in wind resistance, etc.