Stop/start? What we need is drive/neutral....for massive MPG savings

MarkDavis said:
The fuel saving is massive - typically 30-40% - when covering a route and coasting where feasible, compared to the same route when the engine is in gear and providing engine braking. When you're in a gear, the ludicrous the number of times during a journey you for example, see traffic lights 800 yards ahead, accelerate up to them, the brake to slow down.

Yes, its potentially an offence to be coasting but these days with DSG and gears engaging in a few milliseconds, I cannot see why there should be any safety disadvantage. As soon as you touch the throttle for example, the car snaps into gear with a DSG type box.

Government needs to add a 'carve out' in the legislation of the wording to allow for coasting if its built into the car through the gearbox and manufacturers should think about implementing it.
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No No No

This used to drive me insane when I was 17 and my friends thought by putting the gear in neutral and coasting down a hill they were saving fuel.

Why do you think it's impossible to stall in neutral or with the clutch dipped? That's right - because in simple terms the car is feeding the engine petrol to keep it ticking over.

On the other hand, if you keep it in gear and allow the car to slow down enough it will stall, because there is no fuel being injected into the engine to keep it going. Therefore you are better off leaving it in a high gear when going down a hill. (Edit - by this I mean a slight downhill gradient, not a demon slide)

Someone correct me if I'm wrong.
 
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It's pulse and glide ; accelerate to a speed then kill engine and coast. VW are calling their approach 'sailing'. Doesnt really do much for traffic flow though with car speed varying so much.
 
Barks said:
Therefore you are better off leaving it in a high gear when going down a hill.

Someone correct me if I'm wrong.
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NOOOOOOOO!!!!! Select low gear on a hill as you make use of engine braking, using a higher gear means having to use the brakes more thereby causing the possibility of brake fade

Example being there is a hill near me that if I go down in 5th gear with out braking I'll be doing 50 before I get to the bottom, if I do it in 3rd gear without braking I'll be doing 35, both starting the hill at 30
 
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SilverTongue said:
NOOOOOOOO!!!!! Select low gear on a hill as you make use of engine braking, using a higher gear means having to use the brakes more thereby causing the possibility of brake fade
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Don't take the biscuit mate. I obviously meant on a slight downhill gradient otherwise then yes a low gear on a steep slope.
 
Barks said:
No No No

This used to drive me insane when I was 17 and my friends thought by putting the gear in neutral and coasting down a hill they were saving fuel.

Why do you think it's impossible to stall in neutral or with the clutch dipped? That's right - because in simple terms the car is feeding the engine petrol to keep it ticking over.

On the other hand, if you keep it in gear and allow the car to slow down enough it will stall, because there is no fuel being injected into the engine to keep it going. Therefore you are better off leaving it in a high gear when going down a hill. (Edit - by this I mean a slight downhill gradient, not a demon slide)

Someone correct me if I'm wrong.
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Well it'll stall because the engine hasn't enough power to overcome what's stalling it, ie gearing, tyres, clutch, whatever.

When you're rolling on the overrun the engine will typically start injecting fuel as it comes close to idle speed anyway. If you try it on a quiet stretch of road you'll hear and feel it come "back to life" at about 1200-1500rpm
 
Conscript said:
Not sure that's entirely true. If absolutely all fuel was cut, surely the engine would be almost silent?
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If all fuel was cut the engine would have stalled.

Misses the key point though and that is, having the car in gear - any gear - slows the car down and makes a lot more fuel inefficient than being in neutral.

Porsche know what they're doing, and I know what I'm talking about :D

Barks said:
Someone correct me if I'm wrong.
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You're wrong ;-).

All you have to do is turn on the trip computer and measure a few trips to see what's what. It's simple. The naysayers in this thread are speculating about things they have no experience of.

Putting in the car in neutral and coasting, rather than having it in gear significantly reduces fuel consumption. It's as simple as that.
 
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Meh i'm with MarkDavis on this one, depending on the road.

On a very gradual slope / flat road engine braking is the bigger evil over having your engine tick over in neutral, which will use next to nothing in fuel. Having to mash the pedal sooner probably has a bigger impact.

If it's a steeper decline, and you can hold you pace in gear, then engine breaking is preferable. Likewise if you are between traffic lights etc, as you will probably want to actually slow down a bit, etc.
 
MarkDavis said:
If all fuel was cut the engine would have stalled.

Misses the key point though and that is, having the car in gear - any gear - slows the car down and makes a lot more fuel inefficient than being in neutral.

Porsche know what they're doing, and I know what I'm talking about :D
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No it wouldn't stall as the wheels would be turning the drivetrain which in turn would be truning the engine keeping the engine running.

Having the car in gear will use no fuel whereas having it neutral will use fuel. So no you don't know what you are talking about. So go away, do some research and don't come back till you start talking from your mouth and not your ****
 
MarkDavis said:
Put your car in 5th at 40mph and tell me whether how long it takes before you stall the engine.....

Did you fail your 11 plus exams?
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I frequently do this, my Smart (let alone the Z) can happily sit in 5th at 40 ticking over on a flat road with tiny input on the throttle, or if coming up-to a set of lights I can go several hundred yards without any issue.

As discussed above, coasting would use a very small amount of fuel, staying in gear may well use zero fuel. Regardless, any economy saving at this point would be entirely wiped out by other driving characteristics, for example how fast you accelerate away from the lights you've just coasted up-to!
 
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MarkDavis said:
Put your car in 5th at 40mph and tell me whether how long it takes before you stall the engine.....

Did you fail your 11 plus exams?
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In 5th gear there is very little to no engine braking so I can go for quite a while before I get to that point, plus if I was wanting to slow down I'd be using my gearbox correctly and going down through the gears dipping the clutch as I came to a stop. So thats a moot point really :rolleyes:
 
SilverTongue said:
In 5th gear there is very little to no engine braking so I can go for quite a while before I get to that point, plus if I was wanting to slow down I'd be using my gearbox correctly and going down through the gears dipping the clutch as I came to a stop. So thats a moot point really :rolleyes:
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Of course there's engine breaking in 5th. There are also drivetrain energy losses.

And as for no fuel usage, what do you think is powering the engine when you have your foot off the accelerator? Ribena?
 
MarkDavis said:
Of course there's engine breaking in 5th.

And as for no fuel usage, what do you think is powering the engine when you have your foot off the accelerator? Ribena?

You really did fail your 11+ didn't you? :eek:
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Can you not read? If you could you would have seen I said very little to none you would have also seen that it is the wheels turning the engine over to keep it running.
 
Mark I can sort of see where you're coming from - get up to speed and pop it in neutral for a bit. This will save a bit of fuel but not much compared to how much you'll need to add bursts of acceleration and such, to maintain speed. Not to mention the increased efforts. But I do see your point, to a point. You are a rude so-and-so, though.

There can be no dispute though that letting off and leaving it in gear when slowing down for traffic lights etc will use less fuel than taking the car out of gear and using the brakes more. Also a car won't stall at 40mph in 5th. It'll likely be very efficient. I can happily achieve high miles per gallon by cruising at 30 in 5th.
 
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The first cars that cut the fuel injection when coasting in gear were in 1982. They were BMWs with BOSCH K jetronic fuel injection. By 1992, pretty much everything did this and by 1994 every car does.

The simple fact that coasting in neutral requires idle-fueling and coasting in gear requires zero fuel. MPG = distance/fuel-used, so engine braking wins every time.
 
MarkDavis said:
Put your car in 5th at 40mph and tell me whether how long it takes before you stall the engine.....

Did you fail your 11 plus exams?
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It wont stall as once it reaches a certain rpm the car will inject fuel again.

Unless a really big incline comes along.

MarkDavis said:
And as for no fuel usage, what do you think is powering the engine when you have your foot off the accelerator? Ribena?
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What are you on about? The wheels turning is turning the engine over. What if I go down hill and take the keys out? Will the cars engine stop turning instantly as there is no fuel powering it?
 
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MarkDavis said:
And as for no fuel usage, what do you think is powering the engine when you have your foot off the accelerator? Ribena?
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The wheels that are connected to the engine via a gearbox. If you're going to argue that fuel injected cars don't cut fuel off when you lift off the accelerator we may as well close this thread down and call it a day.

MarkDavis said:
Put your car in 5th at 40mph and tell me whether how long it takes before you stall the engine.....

Did you fail your 11 plus exams?
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The car will drop in revs gradually until it starts passing fuel to maintain idle RPM.

Why do you constantly belittle people, you're not as smart as you think you are. You just come across nasty.
 
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I do something similar in my 2nd Gen Prius.

Below approx 44mph, the engine can stop turning. Above that, it must turn but is effectively on shut-off or overrun unless you need the power ( it turns for gearing to protect one of the motors ).

The best thing is, that on this gen prius ( ie. the 1.5 version ), you can get the powertrain into a state where there are no arrows - you're not using electricity to move, and also you're not regenerating - effectively gliding in neutral in almost silence.

The trick is knowing the best time to use this without holding traffic up. Quiet back roads or slowish moving queues are best :D

It takes some doing, and it is rather boring, but if you're a boring geek like me, it can be fun lol
 
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