by larrycavan » Sun Jul 20, 2008 10:50 am
From a SuperFlow SF110 Operator's Manual
A head that measures 10% better at 5 inches of water test pressure will also measure 10% better at 10 or 23 or 145" of water.
The exception to this rule is at lower valve lifts or through small, long passages. Then the test pressure muse be kept above a certain minimum to insure that the flow remains turbulent and does not slow down and become laminar. The minimum recommended pressures are as follows.
Min Lift / Min Test Pressure
.050 / 15"
.100 / 8"
.200 / 5"
.300 / 3"
END SF QUOTE
My thinking on this....
The significance of your low lift flow numbers is not a "one glove fits all" situation either. Many are the factors that come into play regarding the importance of low lift numbers. As such, the importance of how you obtain those numbers is also of arguable significance.
As it has always been with flowbench testing. THE MOST IMPORTANT THING is that you are condfident with your REPEATABILITY OF THE BENCH. Without that, one has no reference data from which to draw a conclusion from their modifications.
At any point during a cycle, the valve can see the depression as a variance, not a static value. The time relationship of the variance may be microscopic in measurement. How important that is to anyone's test regimen can best be understood by the tester's thinking at the time.
Flowbench testing has come a very long way over the years in many respects. Some dismiss it as a waste of time because of the inability to duplicate the dynamics of the running engine. Seemingly the GFN [and I have nothing but respect for DV's opinions on any internal combustion engine theories] approach, at this moment in time, is that floating depression is a better simulation method of live engine dynamics flow.
Is it? I can't answer that with any confidence of being 100% correct.
Rather than concluding things from the GFN articles, I was instead left pondering much of the approach to flow testing.
Over here, we've developed a our own approach to the bench itself and to certain methods of testing that have proven to deliver positive results. Certain test methods have come from some members who are at the top of the class in their professions. Certainly we cannot suddenly dismiss what they have so graciously delivered to our library. At the same time, we cannot lock up the library from incoming information. That would be a huge mistake.
I don't agree with everything I read over on GFN regarding flow testing but I most certainly respect the effort of and the intention behind those specific articles.
I will also proudly state that I feel the PTS flowbench building & calibration approach is second to none. But remember, the reason it got there was from 3 significant things.
1. The contributions of many people.
2. Open minded debating.
3. A desire for continued learning.
JMO
Larry C
Edited By larrycavan on 1216565431