What's this port trying to tell me?

[John F]

I'm dealing with a port that backs up (flows less) at valve lifts over .700, but when I put a small steel ball probe at the leading edge of the short turn it comes back. What would account for this? Is this telling me to lay back the short turn?

[Rick360]

[CFM headman]

i agree with Rick on every head i have worked on and seen thins you lay it back a little and maybe widen it a little and see what that does

[Jesse Lackman]

Why not glue a little ball on the leading edge of the short turn?

How does that ball stop the air from separating?

Does anyone have an aerodynamic engineering description of what that ball is doing to the airflow?

[John F]

I'm awful curious about that too Jesse. I'd sure like to know why the air can get around the turn with a ball sitting at the begining of the turn better than without it.

I'll lay the turn back a little on one of the ports to see what happens.

[86rocco]

[Thomas Vaught]

We saw the same deal on some cast iron heads that would pick up the flow by using a "aircraft rudder" type bump in the floor of the port.

If we actually fixed the short turn the flow was better and we did not need the "Rudder" bump

Tom V.

[gofaster]

Raising the floor ahead of the short turn, making the short turn a larger radius, and widening it all help.

The goal is to slow the flow enough to make it follow the shortside around, instead of shooting straight across it and running into the back of the bowl.

[crazyman]

More than likely the ball is forcing the air flow to lift off the short turn floor hence making the "effective" path lenght between the top of the port and bottom of the port more equal. When you make the "effective" port lenghts equal you get less shear and more effecient flow.

To make the port worse(don't try this), cuting into the short turn radius will make the port lenghts more unequal.
If you draw a side veiw of the general shape of the short turn /bowl of the port you can see how this would change the effective lenghts of the top and bottom of the port.

[Nick]

If you widen and lay back the short turn on a factory small block ford head, you find water in the corners.
I think some heads just need to die.

My latest attempt to build a set of heads flows 20cfm more than the heads that were on my truck, so we'll see if It's any faster.


Nick