SAC or VCO Injectors?
Which is better SAC or VCO injectors? What does VCO stand for? You ask yourself, who
uses a SAC injector? Do to the Emission Standards of today that are higher than ever,
auto makers have switched their injector design. When Dodge came out with the 6.7 liter
Cummins, they changed to a SAC style injector. So all 6.7 Dodge Cummins and GM LLY,
LBZ and LMM all use the SAC style injectors in their light truck applications. SAC stands
for the sack area around the pintle tip (like a napsack). There are two types of SAC
nozzles, micro blind-hole and cylindrical blind-hole. SAC's flow higher numbers
(LPM=liters per min) for a given hole count /size, but SAC itself poses a type of
turbulence causing restriction. While VCO stands for "Valve Covered Orifice", the
needle/pintle would be considered the valve, which covers the orifice. The VCO's have no
fuel-holding bubble in the tip and they are the least restrictive when it comes to flow. The
SAC nozzle actually flow less than the VCO's, but they (SAC) will move more fuel across
the seat. Hence, roughly the same power and less smoke. The VCO's spray pattern have
a more exact penetration to the intended protrusion zone. The VCO's have better flow (not
higher flow) resulting in the exhaust having a higher exit velocity as well. The VCO's tend
to haze when the engine is cold but clean up when the engine warms up. Also people call
VCO's injectors or nozzles, "dirty" injectors or nozzles. The SAC micro-blind nozzles are
clean when cold, but haze slightly when the engine warms up. This tends to be the trend
with big injectors or nozzles. A 250 HP injector in a SAC will make more power ans less
smoke than a 250 HP injector in a VCO design.
There have been some discussions on a bunch of diesel forms on the internet over 7 hole
vs 5 hole injectors. The discussions also included SAC vs VCO injectors. Stock and
aftermarket injectors for 12 valve and 24 valve engines for the most part have had VCO
nozzles. Although now some aftermarket vendors have switched to SAC nozzles. For
nozzles with the same hole specs (number and size), a SAC nozzle will generally make
more power than a VCO nozzle. The answer though is probably found in a comparison of
the spray patterns. Based on spray penetration, spray angle and spray pattern, SAC
nozzles tend to produce a more uniform spray pattern than VCO nozzles. VCO nozzles
are cheaper than SAC nozzles.
When it comes to two injectors with a comparable fuel delivery, one having 7 holes and
the other having 5 holes. The 7 hole injector should demonstrate better fuel atomiztion
because of the smaller hole size. This would account for the observation that the 7 hole
version results in quicker spooling, better low end throttle response, less smoke and lower
egt's. Blackskyracing did back to back dyno runs comparing 5x14 VCO injectors to 7x10
SAC injectors. Both made the same power but with the 7 hole injectors demonstrating the
other advantages listed above. 5x14 SAC injectors would have made more power, but
without them in the back to back dyno runs it is impossible to say how much more. 5x14
CSA is 0.0007697 and the 7x10 CSA is 0.0005498. That roughly makes the 5x14 a 200 HP
over stock injector and the 7x10 a 125 HP over stock injectors. SAC can give a smaller
injector 50 - 75 HP more over a VCO injector. So the 7x10 SAC now acts like a 7x12 VCO
injector (200 HP over stock) or a 5x14 VCO injector.
The conclusion is that for comparable 5 and 7 hole SAC injectors(7x10-5x14, 7x12-5x16,
7x14-5x18), the 5 hole version will make slighlty more power while the 7 hole version will
demonstrate the other advantages listed above. The 7 hole advantages likely come from
atomization, while the 5 hole advantages likely come from spray pattern considerations.
When it come to making a decision, it will come down to your goals. When the goal is
maximum power, the 5 hole version seems to be the better choice. While for a daily driver,
the 7 hole stands out as the better choice.