Fuel Injection system designs

What is known as a Throttle Body Injection System(TBI)?

When fuel injection systems first came into common use, they were designed to utilize either one or two injectors mounted in a throttle body that replaced the carburetor

While this system proved to be reliable:

It was not capable of providing a high enough level of fuel control to meet emission control requirements

Most engines are now built with either:

Direct injection or multiport fuel injection

Multiport fuel injection:

Which has an injector for each engine cylinder

Direct injection:

Where the fuel is directly injected into the combustion chamber

With multiport fuel injection, the injectors are located in:

The intake manifold, with their spray directed toward intake valves

As air enters the intake manifold:

It will flow all the way to the cylinder head before fuel is injected into it

Carburetor Spacers allow for:

Much better air fuel mixing and prevents fuel droplets from falling out on the intake manifold runners

With direct injection:

A high pressure fuel injector is located to spray highly pressurized fuel directly into the combustion chamber

Therefore, only air flows over:

The intake valves and enters the combustion chamber

Fuel then can be sprayed:

Directly into the combustion chamber at an optimized point in the compression stroke

Also, the fuel acts as a coolant to the hot compressed air in the combustion chamber which allows:

The engine to be designed with even greater levels of compression, which further improves power and efficiency