Injector Breakdown

Marker - part name
Black - shim
Red - compression spring
Green - compression pin
Blue - intermediate disk





Marker - part name
Black - feed passage
Red - alignment pins
Green - pin opening/pintle





Marker - part name
Black - pintle seat
Red - sac/blind-hole

Sac nozzle with cylindrical blind-hole.

Marker - part name
Black - pintle seat
Red - sac/blind-hole

Sac nozzle with micro blind-hole.

Marker - part name
Black - pintle seat
Red - nozzle tip

VCO nozzle.

Marker - part name
Red - needle guide
Green - feed passage
Blue - fuel gallery

12v body area where the compression spring is installed and the return passage.


12v body feed passage with edge filter removed.


24v body area where the compression spring is installed and the return passage.


24v body feed passage.

VCO - Micro blind-hole - Cylindrical blind-hole


VCO - Micro blind-hole - Cylindrical blind-hole


Same nozzle, difference in pintle design.

Micro-blind side by side with a VCO, both are 145° 5x0.018".


Micro blind-hole.


Cylindrical blind-hole.

A sac style nozzle alleviates a few issues that are common with the VCO nozzle. Needle steer being the main issue, and also a smaller failure rate since the pintle never contacts the spray orifices. The sac volume plays into the amount of power produced and also the amount of haze or smoke in correlation to the engine size. You can use a larger volume sac nozzle to make a bit more power, but haze will increase as will overall unburnt fuel. There is a balance to provide good hp characteristics yet retain streetability, in a maximum effort platform this would not be a concern.

Needle steer or low lift needle deviation basically is the pintle flexing during actuation, this leads to some orifices being uncovered earlier than the others. With wear this problem worsens, this uneven pattern early in the injection event was attempted to be corrected/reduced by using a secondary needle guide, found in the CR applications. However, due to the overall tolerance issues associated with the secondary guide, they 6.7L has gone back to a micro-blind nozzle to deal with the same issue, simplicity wins. These low lift areas in the injection event are much more subjective to the VCO nozzle due to the fact that the uneven flow is being controlled by the pintle seat covering the orifice, whereas in the sac nozzle the flow is being fed from the blind-hole.

Marker - part name
Black - needle guide
Red - pin
Green - pintle tip

In this picture the needle guide has 3 basic functions; to support the pintle in it's movement, to control the return rate, and also to control the allowed vertical movement of the pintle. If the tolerance is lost between the nozzle and guide, the pintle will stick open, foreign debris is often the cause. Removing material from the upper edge of the needle guide, also known as the stroke-limiting collar, will increase the allowable vertical movement. The pintle tip can also be ground to increase the dead volume in the nozzle tip if in a VCO style, or blind-hole if in a Sac style.

0.015" difference in pintle tip length.


0.010" removed from the stroke-limiting collar.

You can see here how the external sac size does not always directly correspond with the internal volume.

Here are some mie scattering diagrams to give a visual.

8-hole micro-blind sac type.


5-hole VCO.


5-hole micro-blind sac type.


In most cases a VCO nozzle has a greater ignition delay than a micro-blind sac type nozzle. The VCO nozzle often has a cooler flame, greater duration, and greater intensity, whereas the micro-blind nozzle often has a hotter flame, slightly less duration, and less intensity. Flame intensity can also be parlayed into meaning basically the length of the jet, and the ability to penetrate the air density in the combustion chamber.

Image showing spray jet penetration of different orifice sizes over one millisecond after start of injection.

6x0.002" - 6x0.003" - 6x0.004"