Port velocities

[106-1194218389]

OK here is one that I need your input on, all of you. I first flowed my head at 6" test pressure and then did the test again, same setup just raise it to 10" test pressure. Here are the results both corrected with Port Flow Analyzer to 28" test pressure. The port shows a little more CFM and is more stabile at 10", any thoughts. I thought they should convert samo samo.

@ 6" @ 10"
lift CFM stability cfm stability
.050" 31.6 .59 33.6 .51
.100" 66.7 .50 69.1 .20
.150" 99.3 .52 102.8 .41
.200" 127.7 .60 133.6 .45
.250" 155.4 .70 162.2 .65
.300" 181.1 .61 185.9 1.00
.350" 202.6 .89 207.5 1.50
.400" 220.5 1.16 228.1 .74
.450" 237.8 1.55 241.1 .75
.500" 247.9 .98 249.2 .78
.550" 250.7 1.43 256.9 .65
.600" 251.7 1.22 257.1 1.05
.650" 253.2 1.22 260.9 1.05
.700" 255.0 1.53 260.2 .94
.750" 253.4 1.29 261.4 1.21
.800" 256.3 1.15 261.5 .78

[larrycavan]

John,

How do they look when you convert from 6 > 10 using the actual flow numbers?

Converted numbers get the water muddy at times. A couple thoughts are as follows. NONE MATTER ALL THAT MUCH because what you're after is stability / repeatability with reasonable accuracy.

Calibrating a bench with an orifice that has been tested at a given pressure, say 28" for example, should yield the best accuracy when that actual 28" is used during calibration.

Example:

Someone has a calibration orifice that flows xxxcfm@28". Their bench can't pull 28" using that orifice [not enough motors] They calibrate at some lower number by converting their calibration orifices flow down to something they can reach, dial in their Cd and call it good to go.

Under those circumstances / conditions numbers can become skewed. Converted numbers don't always agree for every concievable pressure they might be tested at.

IMO - Better to calibrate with an orifice that your bench can pull the actual pressure with than to use a "too large" orifice with converted numbers.

That's one scenario / possible answer / reasonable explanation.


NEXT:

We get into the muddy waters of turbulence and dynamic flow conditions of a given port.....

As you're seeing through testing, turbulence issues come, go, shift around....because of a multitude of factors.

In your particular port, it's a real bugger to sort it all out because it's so easily affected by small changes. It's not what I'd call a very good device to associate converted flow numbers to.

Combine both aspects of the initial calibration to the sensativity of those ports......ya got yourself a real puzzler..

In your case, I suspect it's more of the behavior of the turbulent port that's causing conversion match up issues.

Don't worry too much about it. Do some conversion testing with a better streamlined device and see where you stand.

6" to 28" is a good long mile as is 10" to 28". Expecting a bent shape with a valve guide hanging down to behave the same at such a spread of depression is kind of asking a lot....NOT That you're asking that....

NOTE: You did mention you saw better dynamic flow behavior at 10" than you did at 6". Wouldn't suprise me if it did flow a little more at each checking lift point at 10" it was smoother flow. Convert up to 28.....that little bit better number carries with it.....

Those are "MY" personal theories on the situation from testing orifices and ports at different depressions over the years. Given enough time, someone could report their bench converts all numbers from all flow conditionns to identical numbers..........I've seen such claims made.

Larry C



Edited By larrycavan on 1207656561

[larrycavan]

John,

Interesting results on the valve mods. Thanks for posting those details!

[hdwgfx]

John what are your stability #s derived from? port velocity averages?

[106-1194218389]

I just had a thought, and see what you thing. We all know that air is compressable. We also know that to increase flow through and orifice or tube or carb jet you increase pressure. I feel that since air is compressible and liquid is not that when we increase pressure the volume increase may not be in direct proportion like we would like to calculate. I am no scientist or physicist so I do not know for sure. btw is Larry Meaux ok? I have not seen him around on the forums for a few days.

[106-1194218389]

[86rocco1]

So if I'm understanding you correctly, with Port Flow Analyser the cfm reading is an averaged reading of some sort and stability would be analogous to something like the standard deviation?

[larrycavan]

The FP1 has a similar feature but it doesn't display anything from the "bounce". You set the FP1 to give readings based on the amount of change in flow. It's a sort of sensativity adjustment.

Off the top of my head, I could probably set sensativity very low on the FP1 but let Excel control stability of the value change while formulating a mean average of the bounce and output it as a "stability" value. Not positive...but it seems feasable.....

[106-1194218389]

Yes that is what Port FLow Analyzer does. It takes a set amount of readings and then takes an average. You can set the number of readings to average. PFA recommends at least 10 readings if you want it to average the stability which is the "standard deviation" and I have mine set at 10. You can set it much higher which would also increase accuracy. 10 is pretty good.

[106-1194218389]

I did another flow test today. I have been flowing at 10" for the last few days instead of 6". I did a flow with just my intake flow adaptor and then I did a flow test with my intake manifold in place. The intake is an Edelbrock Performer EPS manifold. The EPS is optimized for 350 cu. inches and is supposed to add a few horsepower and torque between 3500 rpm and 4500 rpm. So far the intake manifold is stock untouched so the port opening on the manifold is much smaller than the intake port opening of the head. You will notice port is much more stable with the intake manifold in place.

without manifold with manifold
lift cfm stability cfm stability
.050" 33.7 .32 34.6 .39
.100" 68.8 .34 68.9 .34
.150" 102.7 .39 102.7 .32
.200" 135.3 1.72 131.4 .45
.250" 165.4 .91 155.8 .37
.300" 186.2 .73 172.9 .59
.350" 207.3 1.21 183.9 .59
.400" 227.9 .63 192.4 .65
.450" 242.7 .89 199.8 .67
.500" 250.7 .73 205.5 .47
.550" 256.1 .79 210.5 .47
.600" 259.1 .79 214.8 .41
.650" 260.7 1.37 217.2 .24
.700" 260.4 .87 218.9 .52
.750" 263.3 1.17 219.3 .61
.800" 261.5 .96 220.1 .66