Whisteling Port - Whisteling Port @ 15" of Pressure

[larrycavan]

I'd been testing at 10" for a long time. Recently I decided to up the anty and test everything at 28".

I was flowing a 4V head this afternoon that was nice a quiet @10" - .390" lift [max for the cam]. At 15" the whisteling was so loud you practically could't stand it, then as you went up in pressure, it still whistled but not nearly as bad from about 19" on up to 28".....

Curtis?....any input on that? Anyone?

Larry C

[Mouse]

Larry,

Can you change the sound by probing with a beaded wand?

John

[larrycavan]

Haven't tried that yet John. I'll do some more testing tomorrow.

Larry C

[cboggs]

Larry,

I have to admit, I have no idea why they whistle like that, .. ..

but I always flow at 28" and it isn't so bad most of the time, ..

hadn't really givin it much thought, .. :p

Curtis

[Tony]

It sounds rather like vortex shedding may be the cause. I have never heard a head whistle, but here is my theory.

When you have an un-streamlined obstruction in moving airflow, the flow can alternate, first one way then the other around the object. This is caused by flow separation which produces a cyclic pressure variation in the wake. The faster the airflow, the faster the frequency of the fluttering wake.

Vortex airflow meters work that way by measuring the actual frequency. It is also why a flag flutters in the breeze. A very large amplitude slow waving motion at very low wind speeds. In a hurricane, a flag would be almost rigid, but the last inch might flutter so fast it was a blur.

To the sailors here it is "luffing" of the sail. To pilots it indicates incipient stall.

What you probably need is more streamlined valve guides, teardrop shaped, especially on the trailing edge. That hopefully should reduce flow separation. Try packing some modeling clay behind the valve guides to make a long streamlined teardrop airfoil shape, see if that stops it.

I suspect violently turbulent and unstable flow in the port caused by the guide is not going to help the flow numbers. Reducing the port area slightly may (?) actually lift the flow numbers.

This is all completely abstract theory, I have never tried it.

[bruce]

Whats the port velocity? Have you port mapped it?

[larrycavan]

Interesting theory Tony......the flow seems stable but I'll have to probe it and do some more testing. It seems like 15" is the "sweet spot" for the whisteling and if you left it at 15, you could probably drive someone insane...it's that piercing of a sound...


Larry C

[Mouse]

Can you change the pitch by changing your inlet radius?

[gofaster]

Larry, I would recommend running a flag down the port to see if there is a pocket of reversion or extreme activity out of line with the general flow direction. If that shows anything then you could follow with flow balls to try to nail it down. I think you'll find an area of extreme turbulence.

[JRM]

Larry,
are you using any type of port entry tube, or clay. I have seen in the past if you just plop a head on the bench and not have anytype of air foil at the port entrence the thing will whistle like mad.

[larrycavan]

[DaveMcLain]

I wonder if going to a higher depression doesn't really get rid of the the noise but it instead just moves it's frequency up and out of your hearing range......

I've had some ports that whistle at low lift before, a Pro Topline Big Chevy intake port and an EX-514 big Ford cylinder head, both of those are examples that I can think of which would whistle often very loud. In my case they only did it at one lift point and when I opened the valve more it went away. I always thought it was some sort of function of the velocity past the seat being very high and then making the rest of the port resonate.

[larrycavan]

Here's a couple quick pics of the whistler...

[larrycavan]

one more

[Nick]

I Googled "whistles" and found this info



"Typically whistles involve air streams that flutter against each other. Take the typical whistle where the air rushes straight in and curls around. It has to break through an earlier part of of the air stream to get out the top. This creates an unstable situation, with the air streams fighting for dominance. They alternate thousands of times per second, creating high-pitched sound. If you could see the air bursts, you would actually see thousands of tiny vortices (like tornado's) dancing around. The illustration in this link shows vortices being formed in a organ pipe."

Looks like you made yourself a nice "EDGE" whistle there Larry.

Perhaps you ports a fighting for dominance, and tiny vortexes are forming where the divider is in the center.

You should talk to you port and help them to get along.

Reshape the edge of the divider and see if it goes away.

Read:


Nick