I knew it wouldn't take long for these (good) questions to come up.
I'm just concerned that we don't get too hung up on cars designed for maximum efficiency vs maximum power. Some of the methods used to get fuel and air to high horsepower engines resemble toilet bowls and a lot of that fuel ends up not getting burned.
The biggest question I have is; If you are including the vehicle as a whole, weight has to be part of the discussion unless (perhaps) if you assume regenerative breaking on all cars. It's tough to ignore the transformation of energy into heat at the brakes.
Mike
Zeke Yewdall <[EMAIL PROTECTED]> wrote:
Zeke Yewdall <[EMAIL PROTECTED]> wrote:
Are we comparing exactly the same weight/aerodynamics/rolling
resistance car here, with just different powered engines? Or complete
different cars like a metro, corolla, and a ferarri.
I think for otherwise identical cars, a medium sized engine (but
smaller than what most cars come with nowdays) will get better
mileage, because it can accellerate fast enough to get out of the fuel
dumping acceleration, and into more fuel efficient cruising faster.
But if it's to large, it's less efficient at cruising speed because of
low part load efficiency. And if it's too small, it it always trying
futiley to accellerate, instead of cruising. Also, due to real fixed
ratio transmissions, a less powerful engine may spend more time at a
higher RPM, where the fuel efficiency in grams/kWh is less, whereas a
higher power engine could downshift sooner.
There is also the human factor, that a more powerful car will entice
lead footedness and speeding, and thus get worse gas mileage than an
underpowered car that you just accept your slowness....
On 9/13/05, Michael Redler <[EMAIL PROTECTED]>wrote:
>
>
>
>
>
>
> (theoretically) True
>
>
> (IMHO) Engine efficiency and engine size are almost mutually exclusive (very
> few things are perfectly scalable).
>
> If your throttle control is nothing more than a request for more or less
> power AND there is a correlation between a demand for power and a demand for
> fuel AND the thermal efficiency of the two engines are the same, why not?
>
> The only note I would make is repeating Kirk's point, that the
> characteristics of the engine requires the operator to take full advantage
> of the engines ideal running conditions.
>
> Of course, this too is debatable because of the number of variables.
> However, I think that semantics aside, the other factors are negligible.
>
> Mike
>
> Kirk McLoren <[EMAIL PROTECTED]>wrote:
>
> The fuel efficiency of an engine is not a constant. At high throttle
> settings economy is sacrificed for power. ie the grams of fuel used per
> horsepower hour increases. That is why infinite ratio transmissions would be
> worthwhile. And ideally - lossless.
>
> At low loads the fixed burden of the engine becomes significant. Most
> diesels look best around 70% of design max.
>
> Kirk
>
> Greg and April <[EMAIL PROTECTED]>wrote:
>
>
>
> True or False
>
> Underpowered vehicles can be just as inefficient as overpowered vehicles.
>
> Why or why not?
>
>
>
> Greg H.
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>
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>
>
>
>
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