We offer two types of fuel injectors:

The Siemens Deka injectors are a mass-production unit that is a more affordable option that has a flow variance of up to 5%. This is comparable to other mass-produced injector types on the market and is simply an artifact of mass-production. 

The Fuel Injector Development (FID) injectors are custom flow matched race injectors. They have a flow variance of 1% measured statically and 2% dynamically. These injectors are comparable to the popular units from Injector Dynamics but at a lower price point. 

Normally the higher output  the engine is, the more important it is that there is a minimal amount of flow variance injector to injector. A 5% variance on a moderately modified naturally aspirated engine while it could be a big problem on a high output boosted application, particularly if the engine's airflow also varies cylinder to cylinder and the lowest flowing injector is paired with the highest flowing cylinder. 

SOLD AS SET OF 4, 6, OR 8 INJECTORS.

So 4 cyl listings are for 4 injectors, 6 cyl listings are for 6 injectors, V8 listings are for 8 injectors.