e that was standardised was a 90 horse-power
eight-cylinder engine running at 1,800 revolutions per minute, with
a reducing gear introduced by fitting the air screw on the half-speed
shaft. First made semi-cooled--the exhaust valve was left air-cooled,
and then entirely water-jacketed--this engine demonstrated the advantage
of full water cooling, for under the latter condition the same power was
developed with cylinders a quarter of an inch less in diameter than in
the semi-cooled pattern; at the same time the weight was brought down to
4 1/2 lbs. per horsepower.

A different but equally efficient type of Vee design was the Dorman
engine, of which an end elevation is shown; this developed 80 brake
horse-power at a speed of 1,300 revolutions per minute, with a cylinder
bore of 5 inches; each cylinder was made in cast-iron in one piece with
the combustion chamber, the barrel only being water-jacketed. Auxiliary
exhaust ports were adopted, the holes through the cylinder wall being
uncovered by the piston at the bottom of its stroke--the piston, 4.75
inches in length, was longer than its stroke, so that these ports were
covered when it was at the top of the cylinder. The exhaust discharged
through the ports into a belt surrounding the cylinder, the belts on the
cylinders being connected so that the exhaust gases were taken through
a single pipe. The air was drawn through the crank case, before reaching
the carburettor, this having the effect of cooling the oil in the crank
case as well as warming the air and thus assisting in vaporising the
petrol for each charge of the cylinders. The inlet and exhaust valves
were of the overhead type, as may be gathered from the diagram, and in
spite of cast-iron cylinders being employed a light design was obtained,
the total weight with radiator, piping, and water being only 5.5 lbs.
per horse-power.

Here was the antithesis of the Wolseley type in the matter of bore in
relation to stroke; from about 1907 up to the beginning of the war, and
even later, there was controversy as to which type--that in which the
bore exceeded the stroke, or vice versa--gave greater efficiency.
The short-stroke enthusiasts pointed to the high piston speed of the
long-stroke type, while those who favoured the latter design contended
that full power could not be obtained from each explosion in the
short-stroke type of cylinder. It is now generally conceded that the
long-stroke engine yields higher efficiency,