58 Auto Fundamentals
Higher compression ratios can be used in
the V-type engine without block distortion under
load. The short, heavy crankshaft is more resis-
tant to torsional vibration. In the past, V-12 and
V-16 engines were widely used. Current produc-
tion V-type engines are the V-6 and V-8, along
with a few V-10 and V-12 designs, Figure 3-22.
Horizontally Opposed Engines
The horizontally opposed engine, some-
times called a boxer engine, is like a V-type
engine, except that both banks lie in a horizontal
plane. The advantage here is an extremely low
overall height, which makes this engine ide-
ally suited to installations where space is lim-
ited. Figure 3-23 shows a horizontally opposed
engine. It is an air-cooled, six-cylinder engine.
Firing Order
Firing order refers to the sequence in which
the cylinders fi re. Firing orders are given in order
from the front of the engine to the rear. The order
in which the engine must fi re is determined by
the number of cylinders and the arrangement of
the crankshaft throws. Firing order can be found
in the service information for the vehicle being
serviced. Firing orders vary between engines,
and must be obtained from the service informa-
tion. On some engines, the fi ring order is shown
on the valve cover or intake manifold.
Cooling Classifi cation
As you have learned, engines are either
liquid-cooled or air-cooled. Most vehicles use
liquid-cooled engines. Air-cooled engines are
used in limited numbers on modern vehicles,
but are widely used to operate chain saws, lawn
mowers, scooters, and other equipment. Both
types have advantages and disadvantages.
Air cooling is simple and has no coolant to
leak or freeze in cold weather. However, air-cooled
vehicles are very uncomfortable in cold weather,
since there is no effi cient or safe way to transfer
engine heat to the passenger compartment.
Fuel Classifi cation
Automobile engines can use gasoline, diesel
fuel, gasohol (mixture of gasoline and alcohol),
alcohol, LNG (liquefied natural gas), CNG (com-
pressed natural gas), or LPG (liquefied propane
gas). Gasoline powers the majority of vehicles, but
diesel fuel is used in some vehicles. Gasohol, LNG,
CNG, and LPG are beginning to see wider use.
Some gasohol is called E85 fuel. E85 fuels
are 85% high ethanol (grain alcohol), and can
only be used in specially calibrated vehicles,
usually called fl ex fuel vehicles. E85 fuels are
available in many areas. E85 pumps are clearly
marked to avoid confusion with other types of
gasoline, Figure 3-24. Do not attempt to use E85
in a vehicle that is not calibrated to use it.
Biodiesel is made from plants and animal
fats and is available in many parts of the United
States. Figure 3-25 shows a biodiesel pump. Bio-
diesel is interchangeable with diesel made from
crude oil, without engine modifications. Exhaust
emissions are lower when biodiesel is used
instead of crude oil diesel fuel. Most biodiesel
is mixed with crude oil diesel in a 20/80 ratio.
This is called B20 biodiesel. Some biodiesel has a
higher cetane number and may slightly increase
combustion chamber temperatures. When a
Figure 3-22.
Crankshaft, connecting rods, and pistons of a V-8 engine.
Zelfi t/Shutterstock.com
Figure 3-23.
Crankshaft, connecting rods, and pistons of a horizontally
opposed engine.
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