[Subscribe to Daily Digest] |
Let me go into detail.
The more CIDs and cylinders you have the more
friction the engine will have internally, no matter
what.
Yes progress allows for reduced friction in modern
V8 engines, but also allows for similar results
in a 4 Cyl engine, as such friction is in direct
relation to the number of moving parts and also
with CIDs as larger cylinders will also have a
larger friction area.
When I say that e=m.v2 well that is not quite true
cause in fact the energy needed to accelerate
2x mass is more then 2x as much, this because
2x the mass will induce again more tire friction
more drag in most cases and all and every part
used to transfer the power needed to do this will
have to be adapted to the the increased power, thus
again more friction.
As some point it out power loses are also in direct
relation with engine RPM, a small 2.0L engine
that cranks out ie. 240Hp at 7900 RPM will not be
as efficient as an engine that could do the same
as 5500 RPM assuming that the friction losses etc.
are very close.
This is where the EPA test comes into a problem
cause if one uses long gearing to put big V8 engines
in their low RPM band where they have less friction losses
and tests at a speed where drag is low... ie 65Mph
even the biggest guzzling V8 engines will fake great
fuel economy. Any car with long gearing can do this!
If one would add a 6th gear to our SAABs we would
also improve EPA MPG figures.
The picture will howerver look very different when
one tries to accelerate such a car/suv at a given
rate, in which case the engine will be required to
generate more energy to overcome weight, drag, friction
to achieve the desired rate of acceleration, this
type of vehicle might be further hampered by long
gearing which demands more power to match the
acceleration figures.
All car companies know that, and sure enough the EPA
test works in such a way that such cars/suvs will not
be required to achieve a given rate of acceleration
which would highlight their great capability at
converting fuel into CO2 at a very fast rate.
When you take a 4 Cyl Turbo engine, there are some
basic advantages over larger CID engines.
1st. The engine is lighter.
2nd. As there are less moving parts there is less friction.
3rd. During cruise when little or no boost is needed
it is possible to achive very good milage figures.
4th. As there is less weight and friction, such
an engine will be required to produce less power
for similar results of acceleration.
5th. The engine weight per torque and hp produced favors it.
6th. With proper design and installation the fuel mass
needed to achive a given output will be less due to the
the advantages of less friction and more optimal working
conditions. ie. T7 ECU that compensates for ambient air
pressure variations.
EPA tests will not show this on our SAABs cause we
have 5th gears that a relatively short for getting
good MPG figures. In fact our 5th gears are driving
gears not only cruise gears.
So as I said, Weight + CID = More Weight = Bad Fuel Economy
In order to measure progress we would need to measure
the Gallons per 100 miles figure for each ie. 1000 Lbs of car/suv under
harsher acceleration conditions.
example:
a) A 3000 Lbs car needs 4 Gallons for 100 miles
b) A 6000 Lbs car needs 5 Gallons for 100 miles
Clearly b burns more fuel, but far less for each 1000 Lbs
of its weight.
In reality such a test would highlight that todays
V8 engines are still the gas guzzlers they have always been
and that fitting a very small non turbo engine on a car
will require it to work very hard to achieve the acceleration
figures, thus again burn more gas then one would think.
Regards,
Coolknight
Of course I like V8 engines ;)
And no I don't want to get into combustion flamefront issues...
posted by 212.77.37...
, Thu, 4 Apr 2002 09:51:57
, Thu, 4 Apr 2002 15:10:52
, Thu, 4 Apr 2002 11:38:08, Thu, 4 Apr 2002 15:20:54, Thu, 4 Apr 2002 13:18:55
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
