Shifting down to stop or brake and neutral?

[briogio]

I'm curious what you guys think about putting a car in neutral and then just using the brakes to come to a stop. I know you'ld use up your brake pads more but would you save gas?.
I'm not really into shutting off my engine when I'm coming down a hill but would it save more gas to put it into neutral, idle, and coast down?

[PaleMelanesian]

The best option is to start slowing down sooner, so you don't have to brake at all (engine or pedal brakes).

If you do have to brake (downhill to a stop, for example), downshifting and engine braking is the way to go. DFCO (deceleration Fuel CutOff) will stop the gas flow, so you get free braking with no gas used.

[NachtRitter]

As PaleMelanesian said... That's my preferred method too.

[tjts1]

The over run fuel cut off is different on every car. On our OBD2 volvo manual it will only shut off the injectors if you take your foot off the gas above 2000rpm with the engine warmed up and keep them turned off down to about 1300rpm. There is also a 2 second delay built in. If you're at the top of the hill below 2000rpm, the engine will keep the injectors turned ON. With the injectors off the FE gauge pegs at 99mpg while still going down hill at 20-30mph. With the injectors ON and engine in gear the FE gauge shows 50-60mpg on over run. With the engine idling in neutral the FE gauge pegs at 99mpg. The OEMs tune overrun to minimize emissions on the government's standardized test. Shutting off the injectors on over run affects the temperature and therefore efficiency of the catalytic converter immediately after the over run event. Some times its cleaner to keep the injectors running.
On my mercedes running megasquirt I set it up so it shuts off the injectors below 22kpa at all coolant temps (even right after a cold start), all RPM down to 1000 and there is no delay or taper. I also setup the idle air control valve to maximize engine braking on overrun. Its much stronger than any stock EFI car. In normal driving I get at least 50% of my braking done with the engine and this is with an automatic transmission.

[bestclimb]

order of energy dissipation for me is.

Engine off coast (as you stated you don't do this so ignore)
Deceleration fuel cut off with down shifts
brakes.

If you are not wanting to decelerate on a long down hill grade that is not steep enough to hold your speed in gear with the throttle out, engine on neutral coast may work out better than deceleration fuel cut off then accelerating again.

[Frank Lee]

Hmmm... using the brakes to stop? What will they think of next!

[bestclimb]

I have thought about using the f 350 in front of me to stop but that seems like a pain.

[Piwoslaw]

Originally Posted by tjts1

The over run fuel cut off is different on every car. On our OBD2 volvo manual it will only shut off the injectors if you take your foot off the gas above 2000rpm with the engine warmed up and keep them turned off down to about 1300rpm. There is also a 2 second delay built in.

I read in one of Christ's posts that he slows down to a stop by engine braking while keeping the kill switch button pressed.

Or you can disable you brake and flasher lights, like many European BMW owners. That takes the driving experience to a whole new level

[euromodder]

Originally Posted by briogio

I'm curious what you guys think about putting a car in neutral and then just using the brakes to come to a stop. I know you'ld use up your brake pads more but would you save gas?.

Pick your deceleration method carefully.

If you can call the shots : coast to a stop or to a lower speed.
Pick your starting distance to match the start and end speed.
It takes a while to find out how far your car will coast.
It's a fair bit further than you'd have thought

Obviously, coasting with the engine off is more efficient than with the engine on - but it's not my thing either.

If you'll need to stop / decelerate but have a fairly long way to do so : use engine braking (DFCO, see later).
I've found out that coasting with the engine on, is still more efficient than DFCO.

If the above won't stop or slow you down quickly enough : use the brakes

I'm not really into shutting off my engine when I'm coming down a hill but would it save more gas to put it into neutral, idle, and coast down?

Going down a hill, you normally have DFCO : Fuel is Cut Off while you're Decelerating (releasing the throttle but staying in gear)
With a fuel meter (on board, or scangauge and the like) you can check wether your car keeps using fuel or not.

This is also called engine braking, and should be used going down steeper grades.
It has the same effect on fuel economy as shutting your engine off, but without the disadvantages of shutting it off.

What's a steep grade : any grade steep enough to increase your speed beyond the limit (or the limit + your usual extra) when you're going downhill in neutral.


Depending on your car's aerodynamic properties, it'll have a terminal velocity for every kind of gradient.
Mine is 100-110 kph (63-70 mph) on 4 to 5 % grades, meaning I can coast in neutral and maintain that safe speed - on a highway of course.
Any steeper, and I have to put it in gear to control speed.


Try it out

Remember : braking wastes energy.