Whats better for gas? engine braking, or coasting in neutral?

[shenanigans]

so overall what do you guys think is better on gas?


when you idle in neutral, car is at like 900 rpms, less revs=less gas...


BUT under engine braking aren't some of the injectors disabled? So less cylinders, less gas....


SO normal driving whats better, compression braking? or coasting in neutral?

[SilverBirdSeven]

Neutral in my experience. Easier to brake too, saves on gas and brake pad.

[cam98aro]

lower RPMs=less gas

[chris the great]

but it doesnt make as cool of a sound...

[CamaroRalph]

I have tried both techniques (with an aggressive driving style) and coasting had given better results. but, engine braking lowers your braking distance significantly... (really good for when you spot the cop at the end of a big curve on the highway)

[BobbyZ72]

if im driving and i put my car in neutral the rpms stay the same as if im still in drive, but i know the car is in neutral because i can hit the gas and the rpms will shot up. Also if i jack the rear of my car up off the ground and put it in neutral the tires spin just like its in drive, whats up with this???

[98Camaro3.8]

Originally posted by shenanigans:
BUT under engine braking aren't some of the injectors disabled? So less cylinders, less gas....

All the injectors are disabled. You will use no gas during engine braking. ;)

[FunkZ]

Originally posted by 98Camaro3.8:
All the injectors are disabled. You will use no gas during engine braking.

If there is no gas feeding the cylinders, then in theory you could turn the key off entirely while coasting to a stop in gear and it would have the same effect? I can't see how that's correct. If forward momentum alone was the only thing turning over the motor you would not "coast" to a stop, you'd come to a screeching halt.

The fuel tables in the PCM map are based off both rpm and throttle position correct?

I think you save a little gas by putting the car in neutral (or holding in the clutch) and using just your brakes to stop. You use more of your brake pads this way, but it saves gas and probably engine life as well.

[Little G]

If the injectors were shut off, there would be no exhaust noise while engine braking. Try shutting off the key while moving in gear, there will be no noise.

g

[shenanigans]

Originally posted by Little G:
If the injectors were shut off, there would be no exhaust noise while engine braking. Try shutting off the key while moving in gear, there will be no noise.

g

pretty sure there is noise, seems like when I coasted in gear with engine off in staging lanes there was noise... not 100% wasn't paying attention to that, but I will try it again...

I understand that less revs = less gas...

but if injectors disable is it possible things like 3 cylinders @ 4k = 6 cylinders @ 2k?


But this all really gets into how much do the injectors get disabled? all of them? some of them? part of the time?

[shenanigans]

just ran to the store... cutout open.

rode up to 4k, compression braking, shut car off still sounded the same tapped gas to verify it was off, nothing happened..., not even a hiccup, started car up, don't even know its on except the guages, tap the gas and revs rise.

did it twice, so I woudl assume that maybe all the injectors are disabled.


so injectors off > idle?


btw this only includes manuals

[98Camaro3.8]

Originally posted by FunkZ:
</font><blockquote>quote:</font><hr />Originally posted by 98Camaro3.8:
All the injectors are disabled. You will use no gas during engine braking.

If there is no gas feeding the cylinders, then in theory you could turn the key off entirely while coasting to a stop in gear and it would have the same effect? </font>[/QUOTE]In a manual, yes. That's exactly what will happen.

Originally posted by FunkZ:
If forward momentum alone was the only thing turning over the motor you would not "coast" to a stop, you'd come to a screeching halt.

Not sure why you say that. You can turn a motor over by hand with a wrench with the engine off. It's pretty damn hard fighting the compression, but you can do it.

Originally posted by shenanigans:
pretty sure there is noise, seems like when I coasted in gear with engine off in staging lanes there was noise... not 100% wasn't paying attention to that, but I will try it again...

It depends on what RPM you were at. Somewhere around 2000 is where the injectors are enabled/disabled. You can hear it happen. Let off at 4000 and coast down to 1000 rpm. You'll hear the noise when the injectors are started again.

You can also look at a wideband sensor. It won't show any AFR reading because there's only air coming out. That's why you can calibrate a WBO2 sensor during deceleration. When it gets down around 2000 rpm, it'll jump back up to showing an AFR value.


From the LM-1 wideband oxygen sensor manual:

Sometimes it is inconvenient to remove the sensor from the exhaust pipe for recalibration. On EFI
equipped vehicles the following trick can be used:
EFI systems usually shut the injectors off during coast-down conditions (throttle closed and RPM
typically greater than 1500 RPM). In this situation the engine just acts as a car-driven air-pump
and fills the exhaust system quickly with pure air. In this situation the sensor can be recalibrated.
If you need to step on the throttle while a calibration is in progress, you MUST repeat the
calibration.

I can't say how much of this applies to autos, though.

Originally posted by shenanigans:
did it twice, so I woudl assume that maybe all the injectors are disabled.

Did you actually question me? I thought you said I was the F-Body god? [img]tongue.gif[/img] :D

[ February 09, 2006, 08:52 PM: Message edited by: 98Camaro3.8 ]

[shenanigans]

haha yes I did question you!

makes sense, I listen to alot of stuff on the internet but I also in the end like to check things out for myself. [img]smile.gif[/img]

[FunkZ]

If you have your foot off the gas, in gear, and coasting to a stop, if there was no gas going to the cylinders, when you press in the clutch the motor would die.

I've had to pop-start plenty of manuals, and when there's a spark or fuel issue and the motor doesn't catch, popping that clutch out stops you pretty damn quick.

[98Camaro3.8]

Originally posted by FunkZ:
If you have your foot off the gas, in gear, and coasting to a stop, if there was no gas going to the cylinders, when you press in the clutch the motor would die.

The PCM is smart enough to quickly turn the injectors back on when needed. ;)