Ask A Scientist© Engineering Archive

Index Key:   ENG038
Author:      ben brizzee
Subject:     Horsepower of 4-cylinder engines.
How much horsepower can you have in a 4-cylinder engine.

Response #:  1 of 2
Author:      david r munoz
The power output for an engine depends on a number of factors.  First, it
depends on the efficiency, which in turn depends on the engine geometry,
combustion effectiveness (which depends on fuel air mixing, etc.) and also
on the compression ratio.  The compression ratio should be as high as
possible, but is limited by the type of fuel used because auto ignition will
cause undesirable burn characteristics in a spark ignited engine for
example.  In addition to engine efficiency, the power output is dependent on
the amount and energy content of the fuel that is burned.  Therefore, to
know or be able to estimate the power output of a 4-cylinder engine, you
will have to provide a little more information.

The Carnot cycle efficiency for any engine represents the maximum efficiency
that can be approached theoretically.  This efficiency is equal to one minus
the ratio of the absolute temperature of the burning fuel and the absolute
temperature of the surroundings.

Response #:  2 of 2
Author:      wildman jackson
The amount of horsepower an engine can produce is controlled by the volume
of the cylinder (cylinder), i.e. how many liters of displacement.  Some
cars, like small K-cars, have 1.9 or 2.0 liter engines which have about 100
horsepower or so.  Fuel injection can also play a large role in power. 
Overall though, horsepower is usually defined by or is proportional to the
number of RPM's the engine can sustain.  A typical bicycler can only
maintain about 1/4 horsepower in comparison.