travisgod@[EMAIL PROTECTED]
wrote:
>> Depends on the car. An old carbureted car will burn the same amount,
>> within a percent or two. A modern car will burn ZERO fuel if you keep
it
>> in gear, but will burn a constant small amount in neutral to keep the
>> engine spinning.
>
> Sigh. Some hills are insufficient to overcome engine compression,
> especially at high speeds. Gravitic acceleration < drag deceleration
> + engine compression deceleration.
Speed affects wind drag, not the effect of the hill. Here's $.05, go buy
a clue.
>
> JFC, do you guys even OWN cars?
Yep. Restored a few from the ground up over the years as a hobby. Got a
couple of engineering degrees for my "day job," too.
>
>> For an old carbureted car, you're right. For everything built since,
oh,
>> 1990, you're wrong.
>
> Dude, please just shut the **** up. Go find a minor decline and drive
> down it in gear versus not. Find one where being in gear slows you
> down and being in neutral doesn't. This should not be hard to find at
> ALL.
You have an "end user" cursory understanding of how the machine works,
not a clue as to what's going on inside the "black box." Classic 'I turn
the key and it goes' mentality.
Yes, keeping the car in gear applies a certain amount of drag-
specifically the amount of energy required to keep the engine rotating.
Guess what? If you take it OUT of gear, SOMETHING still has to keep the
engine rotating (in a conventional car, not a hybrid). That "something"
is gasoline being burned to keep the engine idling. For modern cars
(most of those made since around 1990) there are a number of built-in
factors that make it more efficient to leave them in gear going downhill
rather than snicking them into neutral:
1) The final drive ratios are very low (numerically) in high gear, so
that the engine speed is quite low when coasting.
1a) On those cars equipped with automatic transmissions, the torque
convertor reverse-coupling coefficient is low, so that the engine speed
on deceleration is even lower, causing less parasitic drag on the car.
2) Idle-fuel-cut-off algorithms in the engine controller shut the fuel
flow off COMPLETELY, so long as there is enough road speed to keep the
engine turning above idle speed. Yes, there's still that slight drag,
BUT if you eliminate that drag by fuelling the engine, its at best a
break-even trade. Its MORE efficient to steal back a little kinetic
energy to spin the engine while burning less fuel than it is to burn
fuel idling the engine while coasting.
The car manufacturers have arrived at this system through thousands of
hours of testing, and YOU are going to presume to tell THEM what is more
efficient? I don't think so. Remember, they fight for every last bit of
mileage to meet CAFE requirements. Saving a milligram of fuel per mile
adds up fleet-wide.
Now, I humbly stand by for your next profanity-laced tirade of
non-technical nonsense.
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