Port Flow Cd's - Valve in / Valve out?

[PJGD]

I have had no direct experience of cylinder head porting or port flow studies, but I gather that it is common to calculate the inlet port Cd which provides a number that can then be benchmarked against other port designs. A number of questions arise:-

1) What is a typical Cd value at full lift for a modern SI engine having a low swirl port?
2) What might the value be for a swirl port in a modern CI engine?
3) Does flow interaction make it change much when you measure the two inlet ports of a 4-valve head individually, and then if you do them both together?
4) Does one typically also measure the Cd with the valve out as well as with the valve in? What Cd value does this valve-out give?
5) If you were to optimise the port geometry for maximum flow with the valve out, would it still be near optimum (but at a lower flow value) with the valve in?
6) How does one flow the exhaust valve and port. If one creates a depression in the “cylinder” when flowing the inlet port, I assume that the blower is reversed so that a pressure is created in the “cylinder”. In this way, correct flow direction is maintained?
7) Again, what are typical Cd values for a typical poppet exhaust valve; valve in and valve out?

Thank you
PJGD

 

[stroker37]

PORT SOUND OR QUIET PORT.

Since I own a superflow 110 and have flowed many harley davidson heads along with porting out the different sizes, it has come to my attention that those of you who think there is no difference between a quiet port and a noisey one should be standing here while i run these heads on the flowbench.
I have done considerable work on a sportster head and noticed that when i put my finger above the entrance to the velocity tube on the intake manifold (simulating a carb) that the sound disapeared and smmothed out the flow and immediately the verticle glass tube jumped DOWN about 4 inches which meant that the flow was now at 6 inches and no longer at 10 inches which is what i use as my base measurement. THIS REQUIRED ME TO INCREASE THE AIR TO THE HEAD WITH THE LEFT KNOB TO BRING IT BACK UP TO 10 INCHES.
THIS SHOWED AN IMMEDIATE INCREASE IN CFM I WAS AMAZED that sound could hurt the flow so much. I visualize the speed of the airflow to that of a smooth road driving at 60 MPH and then when you travel at 160 MPH you will notice ups and downs you never knew existed before. THIS MEANS THE PORT WALLS MUST BE MACHINED PERFECTLY WITH A BORING BAR to avoid diameter changes which will set up eddy vibrations causing a stagnation of flow at the back of the valve. I even took the valve completely out putting clay into the valve guide thinking the valve was somehow causing a bounceback problem..........guess what?.........the port flowed LESS.........YES I SAID LESS with the valve out altogether than in place. i have come to the conclusion that shape is more important and direction of flow than pure port size. However if we can make it so large that velocity drops to nil.......the shockwaves CAN COLLAPSE but the engine will have poor low end torque. THAT IS MY EXPERIENCE. For whatever it is worth. signed nitrogasm@tcq.net an old dragracer from the 1950's and 60's JOHN BECKER MPLS, MN