Using all of this information, you can begin to see that there are lots
of different ways to make an engine perform better. Car manufacturers
are constantly playing with all of the following variables to make an
engine more powerful and/or more fuel efficient.
Increase displacement
- More displacement means more power because you can burn more gas
during each revolution of the engine. You can increase displacement by
making the cylinder bigger or by adding more cylinders. Twelve cylinders seems to be the practical limit.
Stuff more into each cylinder
- If you can cram more air (and therefore fuel) into a cylinder of a
given size, you can get more power from the cylinder (in the same way
that you would by increasing the size of the cylinder). Turbochargers
and superchargers pressurize the incoming air to effectively cram more
air into a cylinder .
Cool the incoming air -
Compressing air raises its temperature. However, you would like to have
the coolest air possible in the cylinder because the hotter the air is,
the less it will expand when combustion takes place. Therefore, many
turbocharged and supercharged cars have an intercooler. An intercooler
is a special radiator through which the compressed air passes to cool it
off before it enters the cylinder.
Let exhaust exit more easily
- If air resistance makes it hard for exhaust to exit a cylinder, it
robs the engine of power. Air resistance can be lessened by adding a
second exhaust valve to each cylinder (a car with two intake and two
exhaust valves has four valves per cylinder, which improves performance
-- when you hear a car ad tell you the car has four cylinders and 16
valves, what the ad is saying is that the engine has four valves per
cylinder). If the exhaust pipe is too small or the muffler has a lot of
air resistance, this can cause back-pressure, which has the same effect.
High-performance exhaust systems use headers, big tail pipes and
free-flowing mufflers to eliminate back-pressure in the exhaust system.
When you hear that a car has "dual exhaust," the goal is to improve the
flow of exhaust by having two exhaust pipes instead of one.
Make everything lighter
- Lightweight parts help the engine perform better. Each time a piston
changes direction, it uses up energy to stop the travel in one direction
and start it in another. The lighter the piston , the less energy it takes. .

没有评论:
发表评论