Better MPG while decelerating or on idle?

  • Thread starter Thread starter mk1_salami
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Sorry to hijack, but:

Ollie's Gadgets said:
However leaving the car in neutral whilst moving is not advised by advanced drivers as it leaves you without any drive.
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why is that?
My mum always goes on at me for doing that because she says i dont have any control over the car like that. I dont see what difference it makes, anybody care to enlighten me?
 
touch said:
why is that?
My mum always goes on at me for doing that because she says i dont have any control over the car like that. I dont see what difference it makes, anybody care to enlighten me?
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because it increases your response time to a given situation.
if you were freewheeling and a situation occured which required you to give it some gas to avoid, you'd take a little longer to respond as you'd need to engage a gear.
this extra response time could be the difference between accident and no accident.

if a different situation occured requiring you to brake hard then it'd take you a little longer to stop as until you'd engaged a gear you wouldn't have the extra assistance of engine braking.
again, this increase in time taken to respond could be the difference between stopping in time and hitting whatever is in front of you.
 
Whilst this thread is accurate in the fact that staying in gear and lifting off the throttle will use no fuel as opposed to coasting, a lot of people are not pointing out the fact that if you rev both cars to 6krpm and let one coast and the other engine brake, the car coasting will travel a lot further than the one engine braking.

This probably negates any saving of fuel the engine braking car may have had as it wont travel any where near the same distance.

I can coast for over half a mile if I drop the car out of gear at 50mph in 4th. The same test with engine braking sees me travel about 2/10ths of a mile.
 
The_Dark_Side said:
if a different situation occured requiring you to brake hard then it'd take you a little longer to stop as until you'd engaged a gear you wouldn't have the extra assistance of engine braking.
again, this increase in time taken to respond could be the difference between stopping in time and hitting whatever is in front of you.
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Dont 'fully' agree here as if I have to brake hard, I invariably have my clutch down at the same time.
 
Almeda said:
Dont 'fully' agree here as if I have to brake hard, I invariably have my clutch down at the same time.
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granted we are talking about fractions of a second between lifting off and having clutch and brake depressed, but even those fractions of a second can make a difference.
 
Thats bad practise I'd say, you dont need to engage the clutch till theres a chance of it stalling and I would rather stall then not brake hard enough.

Neutral in motion is also bad practise, probably something they'd tell you off for in a driving lesson or test. Its something along the lines of not being in proper control of the vehicle, though I agree its hardly a big deal. The right gear is often relevant, like on hills, etc

I used to know someone who'd switch the engine off for more then 5 minutes and hold the clutch in while in 5th just in case. 5 minutes is a very big hill :D (he had a carb car)
 
Engine braking helps slow a car especially if you dont have abs. Leaving it in gear while braking might stall it though. Hence why people (including myself) often dip the clutch earlier then needed.


I wonder if a driving inspector would have any problem with a person who stalled on an emergency stop? Shouldnt do imo
 
silversurfer said:
Engine braking helps slow a car especially if you dont have abs. Leaving it in gear while braking might stall it though. Hence why people (including myself) often dip the clutch earlier then needed.


I wonder if a driving inspector would have any problem with a person who stalled on an emergency stop? Shouldnt do imo
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ok, with you now. ;)
 
depending how high up the rev range you are when you start to brake, leaving the clutch up can have either of two effects.
if your revving hard then there can be times where brake only is the best solution as braking will be assisted by significant engine braking.
at lower revs the engine can work against you and "shunt" you on.
for most people it's too confusing to change techniques halfway through braking hard so clutch and brake is held up as the better solution.
 
While I don't disagree that, in a modern car when off the go-pedal the injectors are supposed to be shutdown using no fuel, I don't understand why the noise of the engine doesn't change. You certainly still hear cylinders firing, it doesn't just go earily quiet, and hence there must actually still be combustion occuring.

I imagine the injectors don't actually fully shut off, just reduce to a point where there is still enough fuel to burn but not enough to keep the engine idling (if it wasn't way above idle rpm!).
 
Tumbletop said:
While I don't disagree that, in a modern car when off the go-pedal the injectors are supposed to be shutdown using no fuel, I don't understand why the noise of the engine doesn't change. You certainly still hear cylinders firing, it doesn't just go earily quiet, and hence there must actually still be combustion occuring.

I imagine the injectors don't actually fully shut off, just reduce to a point where there is still enough fuel to burn but not enough to keep the engine idling (if it wasn't way above idle rpm!).
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No, the injectors do fully shut off. Me and my mate were talking about this a couple of nights ago, has just returned from an Audi course on injection systems, where they had some kind of live demo on this very subject.
 
The injectors do shut off. The reason you still hear a noise is because the engine is still turning over (I thought that was obvious) and is still sucking air in and blowing it out. That makes a noise.
 
The_Dark_Side said:
depending how high up the rev range you are when you start to brake, leaving the clutch up can have either of two effects.
if your revving hard then there can be times where brake only is the best solution as braking will be assisted by significant engine braking.
at lower revs the engine can work against you and "shunt" you on.
for most people it's too confusing to change techniques halfway through braking hard so clutch and brake is held up as the better solution.
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This is exactly the theory that my driving instructor professed. He advised around 2500rpm as the clutch dip point (Was a petrol car). He also advised not to change down the gears when stopping in an emergency, as it can be quite difficult to modulate the braking to be on the brink of locking the wheels with changes in the amount of engine torque drag there is.
 
siztenboots said:
70 in second and dropping the clutch, thats a different type of engine breaking
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Thank god you said that as the dropping a car into 2nd at 70 was a very silly comment. Far from all cars can handle 70 in 2nd without the strong risk of blowing themselves to smithereeens.......
 
Mr Footlong said:
Thank god you said that as the dropping a car into 2nd at 70 was a very silly comment. Far from all cars can handle 70 in 2nd without the strong risk of blowing themselves to smithereeens.......
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FFS it was a joke. Jesus, lighten up :p
 
I wouldn't be so sure, I twice had a complete, total and utter brainfade moment in one of my old STI's and went from full pelt 4th into 3rd and it engaged without issue (you really would have thought would have had the fear of god put into me the first time but stupidity is a wonderful thing :rolleyes: )! Suffice to say my heart completely stopped when I engaged the clutch and easily 11k+ rpm went through the engine but to this day it is still running just fine with it's current owner. I did this on 2 completely seperate occasions btw before everyone thinks I am a complete **** :D. I know of a large number of cars where doing that has resulted in various bits being fired out of various parts of the engine lol
 
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