As I've been thinking about this I've come up with another question.
If the injectors aren't squirting any fuel while going down hill in gear, then wouldn't that negate the need to turn the car off? If it uses zero fuel either way then why would you need to turn the car off? Why not just leave it in a high gear like 5th where there is very little resistance?
Again, it really depends on the hill and the situation. If you need maximum coasting distance for say, going up another hill to get to the next downhill stretch, you would want to leave the car out of gear. If there is a known stop at the bottom and you know you can reach that stop, then leaving it in gear and using the engine instead of the brakes would be better.
Horsepower is how hard you hit the wall, torque is how much of the wall you take with you.
I've been wondering the same thing about coasting and fuel useage, and have even thought about adding a lean burn carburator bypass valve to my motorcycle for coasting.
I also wonder if the EGR valve opens while coasting, so it woudl keep the engine warmer.
I can tell from expearince that even in 5th gear, you slow down a bit with your foot off the gas, altho on hilly streaches of highway I've been able to stay above 65mph, and do coasting like this, and it's hard to tell exactly how much it has helped as I've done some other work recently as well, but it seems to give up to a 4-5mpg boost over compleat foot on gas driving, and nertral engine on coasting.
I have been trying the EOC on long decents to gain max momentum. The EOC feels dangerous the first few times you try it (so do it in a very safe place). After that it gets easier, and I am now comfortable with the technique of letting out the clutch in 5th to spin the engine and recharge the brake vacuum. It seems that this is the best tank ever, including some driving in the rain with 2 passengers, and some dirt road driving...+-46MPG (fuel guage estimate) in the 89 toyota camry 5spd.
actually the vacuum helps the the crank side of the cylinders as there is less air to push out of the way.
No air to push out of the way. It balances out as one pistons goes down another comes up. However, closed throttle coasting with high vacuum can cause more oil to be sucked by the rings and the valve guides. Especially bad in high milage engines. oil in the combustion chamber leads to carbon build up.
Kevin A Thornton
For Speed Equipment, Nitrous Express firstname.lastname@example.org
A little oil past the rings can be a good thing too. In my xB the fuel is still being injected and more is injected if the revs get too high - over 2000rpm I think it burns more - it is supposed to be open loop - when the engine is cool I can feel the extra gas kick in as the braking action is reduced suddenly. I put it in neutral like when I go over the Sakonnet River Bridge taking the exit on the bridge to go south I can coast 1 mile to the Stone Bridge which when you look back is an amazing distance. Only thing else is if it is hot out and the engine is turning faster the water cools better and if you are running the AC then crank up the blower and get some of the energy converted into cold as well as crank up the alternator.
I could motorize it with electric because it runs on a separate belt but I can live with it - nice to be able to turn corners on two wheels like I was doing today - that takes some assist. I am not worried about 0.1-0.2 gallons per hour.