PTS Flowbench Forum

Rick- on the first part about the exhaust in overlap, Which is it? on the one hand you say reversion, on the other over scavenge. If it can overscavenge you must concede that the exiting exhaust gasses produce a greater pressure drop in the cylinder/cumbustion chamber than in the intake port/cumbustion chamber as the piston is vertually parked... On the other hand if it is reversion are the valve events right? is it happening at the overlap phase or at the end of the intake? I understand my earlier statement about measuring vacuum it the headder is oversimplified. if the exhaust did not pull the intake charge to begin with we could not use the overlap period(The 5th cycle) which we do.
On the "small role" the overlap has on the cylinder filling, i disagree. this period is critical as it starts the air mass flowing into the port, in my opinion harder than the ever piston does. i don't feel it is a small role at all. I understand that the mass flow demand during the overlap period in cfm is small because the valve is not open far, yet the depression pulling on this just open intake valve is very large.
To me that is the whole point of testing this way. Use the high depression to find realistic gains around the intake seat/valve at a nearer to real depression, not the shape of the port at max valve lift. why see if the flow hangs on around the short side at 40" if the cylinder only pulls 15 when the valve is wide open?

All that does NOT show an inverse operation of the system how it is.

The engines i typically work on are rules 2bbl engines, so i have seen how much vacuum can be present in the intake at WFO! for sure. in fact the best way to get around the restriction is to pull more manifold vacuum under load full throttle.what better way to "overcome" any depression in the intake tract and start flowing than by applying a greater depression.

I am not the best person to convey all of these ideas for sure. but i feel like the whole point of testing this way is just being missed here. It is not all about the mass flow of a port with the valve wide open 89% having 300fps velocity at the choke with the right mcsa. thats is great and I look for those things too. not sure how much more time i have to work on here about this for awhile. There are other scources better than I for sure check a few out and think on it for a time.

Ok, My point was to bring focus to this exact subject and neither Reversion nor scavenging support the notion that Inverse variable depression testing is some logical manor in which to test. You said “Engines NEVER pull a fixed depression on a port. for this reason alone I believe that testing at a floating depression with a high starting depression is more appropriate. It MUCH more closely simulates what happens in a running engine.” I was just using these examples to say ??? how does this correlate to head testing.

I do not want to get in a pissing match over the theoretical 6 cycles because two of them have no effect on an improperly tuned motor.

Again the point was at split overlap any motor could be over scavenging, creating back pressure due to exhaust restriction or suffering from reversion due to a myriad of things. But the piston is near stopped and engine demand is near mechanical zero yet the variable depression tester is working at its’ peak depression??? I still do not understand your statement of “I believe that testing at a floating depression with a high starting depression is more appropriate.”
Let’s make it clear here I have NEVER said the exhaust did not enhance the intake process in a properly tuned engine and that said, I am a huge believer in testing at many different depressions especially on the exhaust side.

I am not sure where you are taking this thread but I yet to see how the David Vizard variable depression test fixture has shown it is some or any advancement in the cylinder head air flow testing arena.

I will support this thread for the educational facts it brings to the forum but to date I have not been able to see it’s value in testing. Now lets figure out how to get you where you want to be with this device, Some state of calibration? Some method of comparative analysis?

In reading your last post you seem to be focusing your energy on Split Overlap and testing to maximize this area of gain, but to do this would it not be a good idea to test via blocking off the combustion chamber with a stub cylinder (maybe with a piston in it at near position for the valve events) and pull through the exhaust so that the affected flow runs through its normal path. Vacuum starting on exhaust side pull through the intake?? Maybe make the stub out or acrylic and use smoke and other methods to see the air flow.

Rick

I don't see how it is inverse. if the depression IN THE CYLINDER acting On the intake valve of a running engine is higher at low lift than at high lift, how is the rig inverse???? this is how it does it!! Mechanical "0" has nothing to do with it. the depression at that point comes from the exhaust.

Jason,

Again here we are beating a horse, the whole premise is now solely based on the fact that we have a properly tuned exhaust with proper cam timing and that it is in fact scavenging and putting some negative depression on the chamber. All to validate this form of testing? Jason I think you are reaching hear and or putting to many eggs in one basket.

Rick

Okay- so Rick I don't want a p-match either. I have obviousely been focusing too much on the why and would like to get with you and focus more on the how if we can still be freinds (I love u man). we can have differing opinions and still be good if thats okay with you.

What knids of ideas do you have to measure flow on something like this?

My own mind goes to multiple orifice or a auto MAF sensor. I admit too not knowing much about pito stuff.

as an aside, i checked out that plate on top of a bore adapter (as per Rick's segestion)and the results may be inersting.

with the bore adapter on i put on the plate and open holes 160,10 and 5. check voltage, and take a reading on mano.
the manometer reading indicates a flow of 195 on my chart. The superflow 1200 readings for each holes (on top of a bore) in the same order are 182.4, 9.9, 5.2 tallied= 197.5. very similar

I take off the bore adapter and put the plate on the 5" hole in the top with same holes flowing and take a reading. It correlates to 175cfm on the chart, the same as it did when i made the chart on 8/20/2010.

Ther is definatly a gain flowing the plate on a bore adapter.

Jason, if you dangle some string through the holes I suspect you'll see more turbulence below the plate when it doesn't have the bore adapter to help organize the flow.

cheers,
Michael

I should have also included, the 1st reading was 19"h20 the second at 21.25" h20.

19/21.25=.8941

175/195=.8974

am i looking at an 11% gain either case? or is this the wrong way of comparing this?

Jason,

I am in no means unhappy with you I just enjoy a good discussion and to learn, and as you have figured out in no way a big fan of DV and my reasons have been echoed by many across the web. That said it does not make my opinions right they are just mine and I can have them and engage in good banter toward disproving them. I am no flow bench Jedi Master and you are not Luke, there are many here and on other forums that know more but I do have tenacity to research and learn that tires many.

The flow bench is a tool just like others in the shop it is just one of those that once you have one you might just say to yourself how did I do this? Without one!

Here are the reasons I think this is a good project.

1. You learn about monometers.
2. You start to think about airflow.
3. You start to think about what affects airflow.
4. You begin to understand differential pressure.

Here are the reasons I think an orifice bench is better suited for testing.

1. It is ratiometric.
2. It can do either fixed or variable depression or anywhere in between at any valve lift.
3. You can see actual flow numbers not extrapolated data
4. You can record air speeds at a fixed point every time.
5. You can test the port flow at either Mean airspeed or Depression as a comparative standard.
6. Once calibrated you could compare your data to someone else’s who followed your same flow test methodology and calibration.
7. You are more suited to flow other objects such as intakes carburetors and throttle bodies.

For your project I think you need to pin down the following.

1. Obtain some form of a calibrated orifice. Your pseudo Helmholtz plate is buying you nothing and its design is just to dampen any pulsations in the fluid flowing through it. Without two identically made plates it will be very difficult to determine the CD of any of the holes let alone all three combined. If you truly cannot afford one of these then your extrapolated data will be off by the error in whatever plate you have. The reason for this is since you do not have the ability to test one plate against the other so you are unable to regress the CD of a home made plate.
2. Once you have a plate of known CD and flow at a given depression you have a foundation for your extrapolation of air flow.
3. Next you will need to derive you calculation for flow standardization this should include corrections for weather altitude and voltage.
4. You will need to have a temperature probe in the air flow stream between the tested part and the motor/s this is extremely important if you are going to do blow through exhaust testing. Since this device is not ratiometric it will act just like an SF1XX you must make temp, baro, altitude corrections at min. This data can be found on the forum I think I even posted a PDF of the 120 manual someplace.
5. Unless you went to create a two block long incline monometer you will most like have to settle for +/_ 5cfm on your data as with bounce and all that on a vertical anything under 3/8 of am inch will most likely be a visual average.
6. If you are looking for big depression numbers at little flow <50cfm you could use 2 motors pulling in series. My testing of the Surplus Center motors year ago was they cold pull 136” at 0.cfm and 127” at 10cfm once you get to moving a lot of air the benefit of series motors goes away fast. All that said you really need some head room to pull 136” likely my shop has a 14.5’ ceiling. Yes I know you can use a u tube but then you are cutting your reading accuracy in half and I do not think that is a good idea for resolution.

This is a start let me know what your thoughts are.

Rick

Jason,

When flowing an orifce directly over a head adapter it acts like the orifcie in a pipe, this will deminish the VC/CD thus the hole flows more.

Rick

Your % looks good to me.