flowbench design - floaing depression

[JMR]

[thomasvaught-1]

I think part of the reasons why people migrated from other plans and other styles of flow measurement was that this forum offers an excellent set of plans for the money. People here have freely provided accurate information to all questions. People have developed "fixes" for some of the previous "designs" (posted in magazines and on websites) that did not have robust engineering theory in the fabrication of the parts, excessive leak rates, or poorly fabricated parts.

We have a really good flow bench forum here and I am very proud to be a member.

Tom V.

[106-1194218389]

When I used to use the FlowQuik I always just turned the vacuum on full speed and never adjusted it. When comparing my flow tests to other "regular" benchs my lower lift flows were always higher. If I remember correctly about that same amount as noted. If you think of how an engine works the lower lifts would have higher depressions than the higher lifts. The only trouble is "how much"? I would like to test as high as I could, but my budget is a determining factor.

John

[bruce]

[86rocco1]

[larrycavan]

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

[86rocco1]

There are a lot of reasons to be on this forum but the level and quality of the peer review of ones work that you're able to get here is more than reason enough. It ensures consistantly high standards, this discussion concerning the GFN article is evidence of that.

[Sir Yun]

here here LarryC.


I find the measurement method to be not too elegant but the reasoning behind the idea is interesting to say the least. it would suggest that valve seat development should be done at high depression but that pulling 90 '' of depression through a port at full lift is overkill as this would not happen in a live engine..

but this is all still steady state. a running engine will probably cause momentary spikes in pressure waaaay higher and maybe the flowing at higher depression is optimining these events..

quite a bit of people having build HUGE airflow capacity air movers could provide data on the effects of depression.

Larry Widmer seems to prefer non steady state measurements. I can imagine that would privide interesting insight in how a port ''starts and stops''





thanks JMR for doing the test. highly interesting ( i have a FQ on the way. will probably be building a orifice bench in the future as well. ).


i for one an ready to be confused even come about engines that i am at this point



:p

[thomasvaught-1]

zz

[106-1194218389]

[68Corvette]

I wonder why DV is referring to peak torque rpm an not peak HP rpm.
Because peak tq is the rpm where engine has its best overall breathing capability and after that breathing restrictions start to play big role.
They can be cam duration, -lift, intake CSA, exhaust etc. but at least it would be much more interesting for me to see what are pressure differentials during maximum hp delivery.
My guess would be that cylinder vacuum is well beyond 10" h20 even with this specific engine =)

[bruce]

What if steady state testing was merely an extended viewing of a time slice of an actual running engine? ???

[larrycavan]

[106-1194218389]

I went and looked at the Go Fast News article that was showing how to build a DIY cheap flowbench. The floating depression he is talking about there is just simply a way to make a chart to read your test depression only and get your cfm the test piece is flowing by looking at the chart. He shows how to make that Helgesen Calibration plate and then go through the process of flowing it as the test piece on your flow bench. Each hole or combination of holes has a known flow value which he lists at 28" H2O. You use the recorded depression at each combination of hole which you chart out on some graph paper. Your "actual" cfm may not be what is going through the holes, but it lets you convert your "floating depression" reading to a 28" H2O comparison. It is not necessarily a better way to do it, just a cheap way. Just another way to skin the cat. It is an interesting way to do it. It is meant to be used with a flow bench that has a test pressure only manometer. I still like the PTS orifice build myself. It is really not that much more work and is not subject to voltage changes. JMO
John

[larrycavan]