What’s the Difference Between VCO and SAC Fuel Injectors?

We’re covering fuel injectors, specifically the difference between VCO versus SAC injectors.

There are a few main differences that we’ll cover in this article:

  • VCO nozzles tend to be quieter and allow for more power. However, the fuel pattern can be weak at the beginning of the injection event.
  • SAC nozzles are louder, and better suited for mid-level power applications. They also tend to have more longevity.

VCO Injectors

VCO (stands for valve covering orifice) has a moving needle inside the injector. This needle covers the holes at the end of the injector and causes a very clean end to the injection event.

When making big injectors we EDM larger holes into the nozzle. The VCO nozzles have much more material to work with than the SAC style. Because of this, we only like to take a SAC injector up to .020 hole size. In a VCO, we can go all the way up to .028 hole size.

One of the downsides of a VCO nozzle is when it starts to open, the needle is mostly blocking the passage that feeds out of the nozzle. As a result, the fuel flow is weak and the spray pattern isn’t clean at the start of injection.

SAC Injectors

A SAC style nozzle has more of a teardrop shape. A tiny cavity in the bottom of the injector feeds into the injector. A small needle at the end of the valve closes the cavity. This cavity maintains a small amount of fuel in the tip, which helps cool the nozzle and preserve longevity. SAC style nozzles are typically used in marine applications or others with lower emission standards.

On a SAC style nozzle, when the valve moves, the fuel cavity immediately fills with fuel and provides a crisp, clean injection. However, SAC nozzles tend to have more idle noise, and more of a knock sound.

What does this all mean in the real world? If you’re concerned with idle noise, go with a VCO injector. If you want to avoid idle haze, choose a VCO nozzle. If you’re pushing big power numbers, go with a VCO.

If you’re middle of the road power-wise, and can handle a little more idle noise, a SAC injector might make more sense.

If you have questions about what might make the most sense for your truck, driving style, and power goals, give us a call at 435-962-9555, leave us a comment below, or shoot us a message on Facebook or Instagram. We’re happy to help you figure out what will work best for your truck.

Cummins Injectors, SAC vs VCO Nozzles | Power Driven Diesel

6 thoughts on “What’s the Difference Between VCO and SAC Fuel Injectors?

  1. William says:

    excellent video finally a clear explanation on the 2 different styles quick question tho what is the benifit of having say a 7×12 vs a 5×12 what is the difference with having more holes but the same size how does it affect the combustion and performance.

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