Evening star., 1914-01-04
LONG-STROKE MOTOR
HAS ADVANTAGES
Is Considered More Economi-
cal in the Use of
Fuel.
NEEDS LESS RADiATlNG
SURFACE FOR COOLING
Intake Valves Do Not Require At
tention Of Regrinders as Ex-
haust Ones Do.

A prominent automobile engineer in
speaking Of the long-stroke motor now
In use In many automobiles recently
had this to say on the subject:
L would say that the advantages of
lonS-stroke motor over a short-stroke
are: A motor much lighter in weight
for given horsepower: motor Of
longer life: a motor more economical
in the use of fuel; motor requiring
less radiating surface for cooling;
motor of smoother running qualities and
less noise.
1T seems to be the prevailing opinion
that the longer-stroke motor is Of
heavier design. My entire experience
has been exactly the opposite. For an
illustration, take a four by four motor
of modern construction. 1t is bad
design, indeed, If any good designer
cannot copy 1t, changing 1t to a four
by five and a half, making a motor of
as long life at an increased weight Of
from to 10 per cent. In making the
change he will get an increase in
power of from 25 to 35 per cent at
the same number Of revolutions per
minute. He will not have increased the
initial pressure on the piston head, the
shock caused by the instantaneous ex-
Of the stroke, or the pressure on the
bearings. Hence there is no occasion
for increasing the thickness OF the
niston head, cylinder walls or other
parts.
Increase Motors Speed.
"The advocates Of the short-stroke
motor will at once reply that he VIII
simply increase the speed OF the motor
until he gets the same piston speed ana
will then get the same power AT hrst
glance it seems that he is right from
theoretical standpoint. But such Is not
the case. Neither is he correct from a
practical standpoint. In the first place,
the greater the speed Of the motor. the
more the power required TO propei the
motor itself. We must not lose sight OF
the indicated and actual horsepower ana
the fact that the power required to Drive
the motor itself must be considered as
lost. 1t should be quite clear that II
will require more power to turn the
four by four motor greater num-
Der of revolutions per minute to get
the same piston speed as the four by nve
and a half Hence If there were no
other advantage. this increased fricttonal
loss would be the means of preventing the
securing of the same power from the
shorter stroke motor.
There is a speed at which every motor
will produce the most power for the
amount of fuel consumed. 1t Will De
found that the actual pull in pounds Will
increase with the speed Of the motor up
to given point, when the pull in pounds
will begin to decrease. II the speed is
increased beyond this point the motor
will continue to develop more power. but
not In proportion to the increase in speed;
the other hand, below the speed at which
the pull in pounds Is greatest, the horse
power Is not less, but the fuel consump-
ton is greater per horsepower developed.
II YOU test this out fully you will find
that the highest point Of efficiency is at a
higher piston speed on fong-stroke than
on a short-stroke motor. Another reason
why you cannot get the same power from
shorter stroke motor by increasing 1t to
the same piston speed as the longer
stroke Is because of the fmpossibiltty OF
converting into work the same amount
of heat from q given number OF heat
units OF this advantage we shall speak
later under another head.
Has Smaller Cylinder.
"The long-stroke motor of given
horsepower has a smaller cylinder diam
eter, and, as the initial pressure on the
piston head is practically the same in
both long or short stroke construction,
il there is no difference in the diameter
of the cylinders. 1t is clear that the actual
pressure on the piston head in the motor
of a smaller diameter and longer stroke
will be less than in that of larger dame
ter and shorter stroke. and as a natural
result the shock caused by the quick
expansion of the gases at the beginning
of the stroke is less in the smaller diam
eter, the work on the bearings being not
so severe. In the short-stroke motor
practically all parts, with the exception OF
the piston, must move faster. This, to-
gether with the number of reversals OF
direction of motion per unit Of time. must
necessarily mean more wear on bearings.
valves. valve stems and cams.
at is well understood that the intake
valve does not require the attention OF
regrinding the exhaust valve does, the
heat of the escaping gases being respon-
sible for the difference. If we can reduce
the temperature Of the burnt gases as
they are permitted to escape through the
exhaust valve (which is accomplished with
the long stroke motor we to that extent
reduce the cause for regrfnding.
ut has been stated frequently by able
men that the loss through radiation OF
through the cylinder walls Of short
stroke motor was less than in long
stroke motor and that for this reason
the former was more economical OF
fuel. In this opinion we can in no way
concur This argument is based upon
the theory that, the stroke being
longer, more Of the cylinder wall Is ex-
posed, and as a result there Is more
chance for the heat to be carried on
through that part Of the cylinder swept
by the piston. II this were true the
loss would still be less than on the