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Old 06-22-2010, 05:42 PM   #5
Smokem
 
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Name: Smokem
Title: Turbler
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Join Date: May 2006
Location: Iowa
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Posts: 5,565
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.
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Last edited by TMONEYDIESEL; 10-16-2011 at 02:26 PM.