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Drive for show and putt for dough

Posted by Scott Fleenor on

I am often asked 2 questions when testing a set of fuel injectors:

1. What is the difference between dynamic and static injector testing?
2. Why do my injectors have different variances when looking at static vs. dynamic?

I'll start with question 1. Static testing is holding the injector wide open and measuring total flow. This is the measurement you see in either lbs. per hour or cc per minute when buying or planning for performance injector replacement. It is the base flow calibration for any injector. Dynamic testing is the operational testing of the injector. In other words it's the measurement of flow while actually operating the injector through either a fixed or a sweeping pulse. All injectors done by me are sweep tested across an RPM range and Ms pulse duration for a fixed time. This testing tells the story of how the injector is actually working through operating conditions. It's kind of like the old golf adage, "drive for show and putt for dough". Static testing is the drive for show, the big number, and dynamic testing is the putt for dough. You can have the big number, but if you can't bring it home with proper internal operation you have just a big number......no dough!

So why is there typically a difference between my variance numbers? Simple, your injectors have multiple components internally that are electrically driven to move off of their seat and deliver a metered amount of fuel. Any one of the components can have a wear difference that does not allow them to react at the precise same amount as their counterparts, this is variance. When excessive static variance is observed prior to cleaning and service it is typically a cleaning issue with the injector. If after cleaning the static variation is acceptable but the dynamic variation is still too wide, than injector replacement may be required. So it is not uncommon at all for the variation numbers to be different between static and dynamic. I rarely see static and dynamic variations the same.

Now let's talk quickly about the new knock off injectors that are inundating the market. I'm going to vent in another blog about this so I'll keep this short. There is no quality control to speak of when it comes to these injectors. I RARELY see these injectors with good dynamic, or even static variation. This is not a cleaning issue either, it is a replacement issue. I have sets of them on my bench right now that customers have simply left because how junk they are. Like I said, I'm going to vent later on this!!

So what is it for you and your injectors? Do you just want to be in the long ball contest and drive to the big number, or are you going to also have that putter dialed in for the dough?

Peace

Scott


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