On Sat, 29 Nov 1997 13:19:41 EST DANMAS <DANMAS@aol.com> writes:
>In a message dated 97-11-29 I wrote:
SERIOUS SNIP
>Hi, Chris:
>
>I'm going to disagree with you on your first point, and maybe the
>second as
>well. The 15 -20 hp figure quoted is indeed a constant, as that was
>stated as
>the hp REQUIRED to move the car. How much energy is consumed by the
>engine in
>the form of gasoline is a variable, which is by definition efficiency.
>If it
>takes 15 -20 hp to overcome friction, wind resistance, etc, at 60 mph,
>it
>takes that 15 -20 hp regardless of the type of engine, fuel used,
>energy
>conversion efficiency, etc. It doesn't matter if the engine is a
>nuclear
>reactor or a brace of hyperactive chipmunks, the energy supplied to
>the rear
>wheels is a constant, as long as the speed and road conditions remain
>constant. Apply more energy, you go faster, apply less and you go
>slower. If
>you were to leave the emergency brake on, for example, the engine may
>have to
>produce 100 hp to get the required 15 -20 appled to actually moving
>the car.
>The other 80 - 85 hp is spent in cooking the brakes, but that doesn't
>change
>the 15 - 20 hp required - it is a constant.
>
>As to the second point, it takes a SMALLER throttle opening to produce
>60 mph
>in 3rd than it does to reach 60 in fourth, not more (as long as you
>stay
>within a reasonable rpm from the peak efficiency value). The fact that
>the
>engine has a constant displacement is not a factor. Consider going
>downhill in
>4th at 2500 rpm vs going uphill at the same speed in the same gear. If
>the
>down hill is steep enough, you may have to apply negative energy in
>the form
>of braking to maintain the 2500 rpm, whereas going up a steep hill,
>you may
>put the pedal to the floor, and still not have enough power to
>maintain the
>2500 rpm. In both cases, the engine displacement is the same, as is
>the rpm,
>yet there is a drastic difference in throttle position. The difference
>is in
>how efficiently the cylinders are being filled. With the throttle
>closed, they
>may be only 10 % filled, yet in a race engine at full speed, they may
>be
>filled at as much as 120 %! Not only that, but the air/fuel ratio will
>differ,
>from a very lean condition in the first case, to a very rich condition
>in the
>second.
>
>As to economy and efficiency not being tied one to one, I will have to
>agree
>with you in general, but I'm not sure how far apart they are within
>the
>framework of our discussion as it applies to automobiles on the
>street.
>
>Dan Masters,
>Alcoa, TN
>
>'71 TR6---------3000mile/year driver, fully restored
>'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion
>- see:
> http://www.sky.net/~boballen/mg/Masters/
>'74 MGBGT---3000mile/year driver, original condition
>'68 MGBGT---organ donor for the '74
>
OK Dan, I'll buy all that as soon as you convince me that (in the
interests of economy, so as to not wear out the clutch release bearing
and shifter forks), you never shift into 4th gear, but remain in 3rd for
all your cruising.
Rick Morrison
72 MGBGT
74 Midget
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