New-York tribune., 1909-03-21
HORSEPOWER FORMULA
LONG OR SHORT STROKE.
Discussion of the 4 l.. #. ". Sys-
tenn of Determination.
BY Howard F. Coffin.

The retation Of long or short stroke in the actual
determination of the horsepower which will be de-
Hvered on the brake by engine has more
influence than have half dozen other features or
Narfations Of engine design. The development in
the last year abroad Of some motors Of fixed bore
nut nf an abnormaI and commerctally mpraCtable
stroke has had great deal to Dc with the current
discussion of the A socistion o. Licensed Automo-
bile Manufacturers horsepower formula This
Formula. D. = = 2.5, wherein D is the diameter
Of the cylinder y the number of cylinders and 2.5
a constant adopted result of long series
or experiments by the members of the Association
or Licensed Automobile Manufacturers upon mo-
tors Of various types conditions does not It Is
true. take cognizance Of the length Of stroke per
II is also true that some more less Compl-
catad formula be developed that will take into
account the length of stroke. In fact there have
been many Of these formules proposed and dis
cussed upon both sides Of the that, is
usually the case where too many COOKS get a spoon
In the broth, IT would seem impossible to settle
upon any formula that could give universal salts
faction II Is very questionable. also. whether any
such revised formula would he any more accurate
in the end, though it did take the matter of
stroke into account
Matters Of compression. of the design Of the com
hustion space, of the weight Of the reciprocating
parts. Of the size Of valves and Of perhaps half
dozen other considerations. might and do go to
influence the brake horsepower delivered by a
motor fully much more than the length
Of stroke within tho range Of successful com
nerciaI construction
About the same discussion upon this same
Association of Licensed Automobile Manufactur-
ers formula has been going on for a consider
able time in England. where the formula was
originally developed and adopted by the Royal
Automobile Club Of Great Britain and Ireland
The formula has for Its intent a simple. fair and
uniform rating of gas engines Of the usual type
and within the limits Of construction which have
come TO be recognized in the motor car industry
commercially satisfactory.
,1-ili
the scale 10 which the results obtained from this
formula may be applied This same condition
would hold with any formula that might be in
vented, and in fact. it becomes very much
question whether or not greater variations would
be not introduced In any formula in which were
combined any Of the many other Influences that
enter into the actual power delivered by motor.
Even though manufacturer may guarantee
horsepower from 90 to 80 per cent greater than
that indicated by the formula. and the piston
speed which is much higher than that contemplated
by the formula tnamey ! 900 feet of piston speed
a minute). yet the fact remains that this same
motor when reduced TO the common basis of 1000
feet of piston speed minute. Will very probably
not be far away from the result given by the
formuls might at first appear
In any event It may be pretty generally assumed
that any other motor OF the different diam
eter of cylinder. when placed upon the same basis
Of 1000 feet Of piston speed a minute. will bear
a power relation to the first motor entirely IN
cordarce with the formula.
This Association Of Licensed Automobile Manu-
faeturers' horsepower formula is a safe one for
the buyer in that he may always figure II as the
low SIDE Of the actual power OF good motor.
The fact that speeding UP OF the motor 50 that
the travel Of the pistons over the surface of the
cylinder walls viii be much greater than 1000 feet
a minute will enable the manufacturer to produce
and guarantee a horsepower greatly in excess of
that indicated by the formula has bearing what
ever upon the very definite and very practicable
uses Of this formula basis OF comparison of
the performances OF gaSolene engines.
A simple concise and definite formula is of the
greatest Importance the present time in matters
pertaining 10 legislation governing the use OF
motor upon the public highways and is the only
proper basis for the taxation laws which are being
enacted in various sections ot the country. We
understand that this formula has already been so
adopted in several 81 the states where such laws
have been made.