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Importance Of Injector Flow-Matching


Injector flow-matching, also called blueprinting, is an excellent means to improve the engine’s performance and efficiency.  Since each cylinder is essentially metered individually, it only makes sense that the engine would perform better if each cylinder received the exact same amount of fuel.


This flow-matching theory can be demonstrated by the following example. A GM 350 TPI fuel injector is rated 22 lbs/hr at 43.5 psi.  Due to manufacturing tolerances, it is extremely rare to find that all 8 injectors from a particular engine would flow exactly 22 lbs/hr.  If one cylinder’s injector flowed 5% less, then that cylinder would only receive 21 lbs/hr of fuel (0.95 x 22 = 20.9).  1 lb/hr less fuel roughly translates to a potential loss of 2 horsepower for that cylinder.  If 4 injectors were 5% lean, that would translate to a potential loss of approximately 8 horsepower.


In reality, it is not unusual to see flow rate differences as high as 10% between cylinders.  The situation can be aggravated further for in-use injectors which are susceptible to deposit formations which clog metering orifices.

A flow-matched injector set should be matched at more than one point on the flow curve.  Flow-matching at the injector’s static flow alone does not produce a matched set.  As was discussed earlier, injectors are rarely, if ever, operated at static flow.  Therefore, the set should be matched at a dynamic flow point, preferably the manufacturer’s calibration set point (usually around pw of 2.5 msec).  With a set of injectors that are matched at their static and dynamic points, you can be assured that they will flow almost identically through the entire flow curve.

So a flow-matched injector set will not only help produce more efficient power at W.O.T., it will help engine performance through the entire rpm range.  In many cases idle quality, throttle response and overall driveability are noticeably improved with a flow-matched set of fuel injectors.


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