How much does the bore size matter when flow testing?
It would be in our best interest to say that you need several different bore sizes to accurately flow test, let’s say, small-block chevy heads because when going from 4.030” to 4.155” it will make a “measurable” difference in the flow numbers.
Yes, we wish this was true because we could sell more Aluminum Cylinders and Sliders. Well, the truth is … the flow numbers do not change when going from 4.030 to 4.155” bores in back-to-back tests. We have performed this type of back-to-back test on several different types of cylinder heads; we have not found a measurable, repeatable difference when the bore size is changed.
People are incorrect when they state that to accurately flow test you need to “exactly” reproduce the bore size on the motor. Through our testing we have found this to be incorrect.
Our recommendations; Purchase the most popular bore size for the heads and motors that you are building. If a head come into your shop that is used on larger or smaller bore, go ahead and flow test on the 4.030” bore fixture. This approach will give you accurate, repeatable data and will save you both time and money.
I do not know about you, but in our shop we have plenty of tooling that came in a “package” that we never use. We have done the research for you on the flow bench equipment, so there is no need to spend your hard-earned money on fixtures that will be just laying around.
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