Going Downhill , Use Neutral Or 5Th Gear ?

[dcc 855]

tbh just google hyper-miling

[GLPoomobile 958]

If you turn the engine off (not recommended while driving) whilst still in gear then you will not notice any change in the engine sound as it will still be turning over without any fuel being injected.

I've never actually tried this, but when thinking about this particular topic in the past I've often wondered if this really is the case. Remember that the noise an engine makes is a combination of valve train noise, as well as combustion and the resultant exhaust noise. If you cut the fuel, you'll still hear the engine turning, but surely the exhaust noise will completely change as you've no longer got combustion going on, just air being pulled in to the engine and forced out of the exhaust.

 

I hate it when people put their cars in neutral to coast.. it's basically them silently telling you they know nothing about cars or driving.

That'll be me then.

 

Since getting my 166 I've become rather obsessed with trying to squeeze every little extra drop out of it's already terrible in-town economy. As Omri said in his OP, let's put safety aside as frankly I give not one single s*it about whether coasting is being out of control (driving instructors would have you believe that feeding the steering wheel is the safest way of turning, and that's another debate for another day). I frequently coast in my Alfa, because it's proven (by me) to be the most economical way on my daily commute. At the relatively low speeds I'm talking about, I can cover greater distance coasting in neutral using a small amount of fuel, than I can coasting even in 6th gear. I've been doing the same short journey daily for 2.5 years and I've seen the difference this one single change makes on my journey, and I'll stick to it regardless of what anyone else thinks.

 

P.S. I realise Omri was specifically talking about going downhill. Clearly if the ECU does indeed cut fuel completely below a certain RPM off throttle then going downhill in gear is going to be more economical, but as my comments above allude to, you have to take in to consideration the distance you can actually cover using both methods for the real answer.

Edited June 22, 2013 by GLPoomobile

[AndyCrom 64]

Would you not make it to the bottom of the hill quicker than 8 minutes if you roll in neutral, because of the car being able to gain a larger speed than 35mph by having no resistance of the gearbox,

Which I see what you are saying is still using some fuel to tick over, but because of rolling I can now carry on with the speed gained from the hill along the following flat, where as the car in gear is now needing to use fuel again and be driven in gear to get to the same point.

 

granted the other car needs fuel to.carry on after the 6 miles but after saving half a litre on fuel i could drive another 3 miles on the savings, but as Sir Isaac Newton said L over D max and with the 205's drag coE you'd have to be rolling at 195.74mph after the 6 miles all in neutral to cover the 3 extra you'd need!

 

Ooo this is sooo interesting but pray what would it be like uphill?

the same as the other car i would have thought lol

[omri617 18]

Assuming that the car is over 1800 rpm and the cut-off fuel mechanism is working.

When putting the leg on the gas pedal , should I feel something special? Any bump or revs up or down or anything?

[Goliath 94]

I've never actually tried this, but when thinking about this particular topic in the past I've often wondered if this really is the case. Remember that the noise an engine makes is a combination of valve train noise, as well as combustion and the resultant exhaust noise. If you cut the fuel, you'll still hear the engine turning, but surely the exhaust noise will completely change as you've no longer got combustion going on, just air being pulled in to the engine and forced out of the exhaust.

 

 

 

Sorry I should have made that sentence clearer. I meant if you are in gear and off the throttle then turning off the engine will not change the sound of the engine as with the car in gear and off the throttle there is no combustion happening anyway.

[GLPoomobile 958]

Sorry I should have made that sentence clearer. I meant if you are in gear and off the throttle then turning off the engine will not change the sound of the engine as with the car in gear and off the throttle there is no combustion happening anyway.

Yeah, I understood what you meant. But when rolling in gear with no throttle - when the engine should theoretically be using no fuel - cars generally don't sound any different to if they were coasting at idle (slight difference in revs aside). Or at least that's my experience of any car I've ever driven anyway. That's why this confuses me, because I'd expect a car to sound different (quieter) if the combustion process has shut down and it's coasting by it's own momentum. As I said above, I'd expect to still hear the engine turning, but would expect the exhaust to be much quieter as there's no combustion taking place.

 

I'm going to have to test this tomorrow and pay more attention to what it sounds like

[Goliath 94]

Yeah, I understood what you meant. But when rolling in gear with no throttle - when the engine should theoretically be using no fuel - cars generally don't sound any different to if they were coasting at idle (slight difference in revs aside). Or at least that's my experience of any car I've ever driven anyway. That's why this confuses me, because I'd expect a car to sound different (quieter) if the combustion process has shut down and it's coasting by it's own momentum. As I said above, I'd expect to still hear the engine turning, but would expect the exhaust to be much quieter as there's no combustion taking place.

 

I'm going to have to test this tomorrow and pay more attention to what it sounds like

 

Ah I see what you mean, it doesn't sound much different on a standard car as the combustion sound is pretty muffled, it's much more noticeable if you listen to, for example, a throttle bodied GTI6 going round track, the BWARP when on full throttle is awesome and changes dramatically when the driver lifts off into a braking area.

[omega 82]

but surely the real fun when you are coasting is when you switch the ignition off give it some gas then wait till you next to some old people/chavs/girls etc switch the ignition back on,theres a loud bang as the unburnt fuel ignites everyone jumps and hopefully your silencer dosnt split.

or is this not the done thing?

[Ryan 99]

That only works on cars with carbs. With injection the injectors won't fire with the ignition off.

[AndyCrom 64]

Well after just connecting my digital tacho to the coil and an LED on a long pair of wires from a injector connector i found that on my 1.9 under engine braking conditions that the LED stopped flashing from injector fuel pulses at any rpm above 1670ish

 

ego the injectors don't fire above 1670 while engine braking

 

done

[welshpug 1,657]

but surely the real fun when you are coasting is when you switch the ignition off give it some gas then wait till you next to some old people/chavs/girls etc switch the ignition back on,theres a loud bang as the unburnt fuel ignites everyone jumps and hopefully your silencer dosnt split.

or is this not the done thing?

 

 

certainly not the done thing and is what the chavs round here do.

[farmer 328 1 Cars]

certainly not the done thing and is what the chavs round here do.

 

Maximum maturity from Welshie once more.

 

The pillar of the Cardiff community.

Edited June 23, 2013 by farmer

[omri617 18]

Well after just connecting my digital tacho to the coil and an LED on a long pair of wires from a injector connector i found that on my 1.9 under engine braking conditions that the LED stopped flashing from injector fuel pulses at any rpm above 1670ish

 

ego the injectors don't fire above 1670 while engine braking

 

done

 

I think we got a straight answer here..

Can you give us the exact details on the conditions of the test?

One thing I don't understand :

 

Going downhill , 70 Mph , 5th gear. REV's are above 1670 - let's say 2000+

You say injectors stop working, what happens if you put Neutral? Do you feel anything when the injectors get back to work?

Edited June 24, 2013 by omri617

[Goliath 94]

Maximum maturity from Welshie once more.

 

The pillar of the Cardiff community.

Pardon?

[dcc 855]

some complete and utter idiots have come to light on this forum recently. bit of a shame.

[Slo 283 1 Cars]

Pmsl

[Goliath 94]

some complete and utter idiots have come to light on this forum recently. bit of a shame.

 

Yep, it's always the minority that spoil it for the majority.