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Port Injection

Introduction to Engine Tuning

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So Port Injection is the same as Indirect Injection?

Kinda, others may have a slightly different view, but I consider there to be four basic injector positions.

The first, 'direct', is when the fuel is injected directly into the combustion chamber - as an aside, all diesels work this way.

The second, and most common, is 'port' or 'runner' injection, where the injector is placed between the valve and the plenum, or butterfly for IRs.

The third, and fairly rare now, is when the injectors are incorporated into the throttle body - most V8 EFI conversions use this method as it's much simpler to bolt the TB in place and it doesn't need other manifold modifications. Some early OEM EFI applications also used this method.

The last is where the injectors are placed at the inlet to independent runners, AKA ITBs, even actually outside. This is used on very high rpm engines as it's needed for proper atomisation/mixing of the fuel and air.

There are also variations which use two, even three, of these basic placements, but they tend to be very specialised for specific applications.