Coasting or keep it in gear?

[soniccj7]

I just watched the following video from another post, and found it very interesting, that he states a modern engine does not use any gas while slowing down. I always thought even during deceleration, the engine was burning fuel.



http://www.youtube.com/v/CQ4w7JSRcoE...d0d0&hl=en_US&


What are your thoughts?


ED

[SlingShot]

Anytime it's running, an engine is burning fuel ...

[tangorover]

I heard about that too. My Old MX6 had that. If you are decelerating theres barely any gas being used. I guess the best way to know is to have a pipe that runs from the tailpipe to your (partner's) nose and see if there's any combustion when the car is decelerating LOL

Just kidding!. If you guys have ever shut off the engine while going downhill and restarted it (by releasing the clutch) ull know that the transition from a Freely turning engine to a combusted engine is quite a jolt. So by that logic I dont think the car dosent use any gas at all. Its probably using whatever the computer calculated vis the Throttle position sensor.

[SSRich]

they still will use gas like when i go off the mountain i put it in neutral and coast at 750rpms if i leave it in gear its between 1500rpms and 2000 rpms. the more rpms you are the more gas it uses

[tangorover]

Originally Posted by SSRich

they still will use gas like when i go off the mountain i put it in neutral and coast at 750rpms if i leave it in gear its between 1500rpms and 2000 rpms. the more rpms you are the more gas it uses

Actually the cas wont depend on the RPM's Most Fuel inected cars dont have a real corelation between the position of the throttle and the amount of gas in the air fuel mix. The cars use the throttle position as one of the variable's to calculate the amount of fuel. Thus when you take your foot off the gas while in gear BAM 0 throtle position so same amount of gas as Idle. Try that in a car with a instant fuel gauge.

[PAUL SS]

Time to study up on hypermiling.

http://www.hypermiling.com/car-mpg.html

[Smart Line]

Originally Posted by PAUL SS

Time to study up on hypermiling.

http://www.hypermiling.com/car-mpg.html

Interesting read

[mhood]

Originally Posted by Smart Line

Interesting read

Interesting yes, but if you think I'm going to drive my SS to get hyper mileage, you're wrong.

[chevydrvr]

http://amasci.com/amateur/traffic/trafexp.html

I read most of that and I wish everybody did that. I feel like if it was taught to new drivers and put on the news or something and everybody used that technique, traffic would not exist anymore.

[Mach]

So whats better for petrol when decelerating to a stop sign or red light??? Leave it in gear or shift to neutral?

[VenomZ302]

Originally Posted by chevydrvr

http://amasci.com/amateur/traffic/trafexp.html

I read most of that and I wish everybody did that. I feel like if it was taught to new drivers and put on the news or something and everybody used that technique, traffic would not exist anymore.

Exactly. I drove up to North Carolina for the weekend of the 4th of July this year and noticed that 90% of the stop and go traffic was caused by stupid people wanting to go faster by eliminating the space between them and those in front. Of course, when those in front aren't going faster, you have to hit the brakes, which causes the people behind you to hit their brakes, and so on and so forth.

More people need to understand physics.

[Apex Paul]

Originally Posted by mhood

Interesting yes, but if you think I'm going to drive my SS to get hyper mileage, you're wrong.

I wouldn't do that either, but I did do it in my Jeep Wrangler as an experiment. My Jeep gets about 15 mpg in my average driving. During my "experiment", I just limited my speed on the interstates to 55 mph. That's it. everything else was the same. My average over two tanks of gas went up to 19 mpg. That's a pretty good increase if you consider the percentage gain.

The gain in a tank would be about 64 miles (4mpg x 16g tank). 64 miles / 15 mpg means I would save about 4.2gals per tank or about $12.33 per tank (which lasts me about a week). That's $641 a year.

Wow, now that I'm looking at the math I feel like I should go back to the slower speed.... nah.

[Kennyspec]

Its called DFCO, Deceleration Fuel Cut Off. My coblat has it, as verified with the wideband and HP tuners. Basically it cuts off ALL fuel during decel. you can even feel the car "jolt" ahead a little when it kicks back in. I am pretty sure the camaro has this feature as well. i just havent checked it yet with hp tuners.

so yes leaving it in gear and downshifting will get better mileage as you are in DFCO.

[mhood]

I did it once in my wife's Jetta diesel...I got bored and gave it up though.