Throttle Body Injection vs Port Fuel Injection vs Direct Fuel Injection. The three types are variants of
fuel injected petrol engines. They are all improvements over
carburetor engines but you will see that fuel injection has
also improved over the years as the various fuel injected types have been introduced.
A direct injected engine can be identified by a clicking sound if you listen to the engine idle with the bonnet
open but this clicking sound is not heard from the interior of the car.
Throttle Body Injection
The throttle body injection is the most basic type of fuel injection that can be found on vehicles
The throttle body was the improvement on the carburetor and while it may look different,
it is similar in design to the carburetor. The fuel injectors are located in a central housing and
the fuel travels with the air throughout the intake manifold on it's way to the cylinders.
This type of fuel injection is like a computerized carburetor so it will benefit from the
precise delivery of the sensors, but there are disadvantages as all of the fuel may not enter the
Port Fuel Injection
Port fuel or multi point injection is an improvement to the throttle body injection as injectors are
placed directly above each intake valve resulting in a more precise fuel delivery. The air and fuel meet at
a later stage than the throttle body so condensation of the fuel is reduced.
This may be a complicated compared to the throttle body but it offers more power with better
fuel economy as more of the fuel can be utilized on each power stroke.
As good as port fuel may sound, engineers have improved on this type of fuel injection and this improvement
is known as direct fuel injection or gasoline direct injection (GDI).
This type of fuel delivery operates similar to the diesel cycle as
the fuel is sprayed directly into the cylinder and mixes with the air. With the use of
common rail technology and advanced injectors the fuel is sprayed at a much
higher pressure causing the fuel to enter the cylinder as a very fine mist which is ideal for a better ignition of
This method decreases the surface area in and around the cylinder where the fuel can come in contact with
before it ignites so a higher percentage (possibly all) of the fuel will be utilized for combustion resulting in
more power per stroke.
GDI results in greater fuel economy and power as less fuel may be wasted. Direct Injection maximizes the benefits
of forced induction as the fuel will not mix with the heated compressed
air before combustion making the direct injection the most efficient of the fuel injection types.