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Originally Posted by freebeard
Or is it free?
I drive a carburated, 4-cycle four cylinder engine with manual transmission. No power steering/brakes/anything.
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The good part is, you don't need to have the engine running for anything of the above, as it simply isn't there.
So you might as well shut it down.
Give it a try on some deserted road, and see how you feel about it.
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I typically descend moderate hills (these days) with clutch in and key on (for safety and ignition of any gas from the idle jet).
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Put the transmission in neutral as well, then you don't need to constantly pull the clutchplates apart. The clutch system is made to be engaged, if you constantly put a load on the mechanism to disengage it with the clutch pedal, that'll increase wear over time. Which may or may not show up.
It also saves some drag in the gearbox.
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In the South hills of Bluegene, it's clutch out and floating the valves against a closed throttle.
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That's engine braking .
Good when you need to stop or control downhill speed.
In other circumstances, it's just as if you're using the friction brakes : wasting energy.
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Nothing to be gained from being in neutral except pain, right?
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Being in neutral on moderate hills means you'll coast down a lot further and/or faster than while in gear.
But the engine is idling unless you shut it down.
Even with an idling engine, you should see a benefit from coasting in neutral over engine braking - simply due to the extra distance covered by not braking.
If you know how many gallons/h your car uses, you can calculate what your minimal coasting speeds with the engine on will be before it starts using more gas (as you don't cover much distance /h when you're going slow). Back in the day, that figure was in some cars' manuals.
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In town I use a closed throttle to respond to lights and changes in traffic, while reserving the brake.
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That's good, but try to go one step better and coast instead of engine braking.
It means you'll have to look and plan even further ahead, and keep your initial speed low(er) as you'll coast a lot further.
If you're OK with shutting the engine off, that'll give the very best fuel economy.