Hypermiling

[aircraft engineer]

depending on how long the light is (I drive some routes where I KNOW the approx time the light will be red) I just stick it in N and turn off the IGN.

 

Restart takes less gas than idle - the break point is about 30 secs

[welly]

Imagine what gas at $8.35 for US gallon does to your driving style and number of journeys you make. Mind you I still do 8000 miles a year on my motorbike just for fun (aka as "wasting fuel" if you're not a biker)although at 45 mpg it is a bit more frugal than the subaru. With 3 vehicles I get through $800/ month just putting gas in everything.Its frightening sometimes.

[rverdoold]

Holland just broke the record in Europe with fuel prices €1.66 per liter no worries its only 10.16 USD per US gallon. My driving style completely changed. Usually not going over 3k rpm coasting a lot for corners, looking ahead FAR ahead on what is going on. I have an automatic which is actually more efficient in upshifting in cities. Tire pressure is also high 40 PSI. I have no A/C and get about 28 to 31 mpg.

Some politicians said that it would save lots of lives if all cars have their lights on during the day. But some stupids say it increases milage to much (government = stupid)

[McDave]

I don't know the specifics of the Subaru engine management software, but Hondas used to incorporate a full fuel cut when coasting in gear untill the engine RPM dropped to 2500 rpm or below. The best strategy would be to learn the fuel cut rpm threshold, by observing injector pulse width on a scan gauge (or looking the decel fuel cut RPM up). Coast in gear until you reach the threshold, then shift to neutral or declutch. (You'll be able to coast further without add'l engine braking, and the injectors will be on below the RPM threshold anyway.)

 

Nathan

Correct! I believe the low threshold may be even lower though. On auto transmissions with lock up torque converters the converter will unlock at about 1200 rpm to keep the car from chugging... like a manual left in gear approaching a stop. At this point the fuel would have to turn back on to maintain idle speed since you lose engine braking, as you would when pushing in the clutch on a manual. Though fuel used from idling is less than from leaving it in gear and having engine braking shorten the distance traveled. It's amazing how far you can often coast in neutral.

 

As far as stopped at a light: In gear the idle air control valve has to open further, so as a result more fuel would have to be added to maintain stoich a/f ratios. May not be much but every bit counts with hypermilers.

[Gloyale]

I could be mistaken, but I could have sworn I read before (maybe on this board) that when "coasting" in gear, the fuel injectors either cut or reduce fuel consumption (since the moving of the car keeps things rotating).

 

Except that only happens when the throttle is fully closed, which isn't coasting so much as braking. You slow down pretty quick. Most of the time to coast, and not lose momentum you would need to have your foot slightly on the gas, which would keep the injectors firing at whatever RPM you are running.

 

If you are trying to *coast* for a longer distances, putting the car in neutral (better for the throw out bearing than keeping the clutch depressed) let's you keep way more of your momentum, resulting in further distances without having to use any more gas than idling.

 

For automatics, shifting in and out of gear while at speed CAN have a negative affect on the one-way "sprauge" clutches and planetaries. You'll save more gas by shutting off the engine at lights. Just remember to put the shifter in nuetral(or park:rolleyes: ) so you can restart.