who knows about retrograde flow

[chargd72]

I'm doing some headwork at home and ready to attack the exhaust ports.  Intake runners are done but I came across this write-up and it intrigued my curiosity.  I'd like to get a few opinions on if the red highlighted portion below sounds legit about exhaust ports and retrograde flow.  


To port match the head, simply cut to this line of paint. Now, blend back into each port about an inch to create a smooth transition between the port opening and the port runner. Use the 3/8 inch round nose cutter for this job. Do not be concerned about the large amount of metal that needs to be removed from the lower edge of the exhaust ports. However, do not try to create a straight line from port opening to the valve seat. It is likely that the water jacket will be cut into if this is attempted. Chrysler small block heads do not flow exhaust gas particularly well, due to a retrograde flow along the floor of the exhaust ports. This "riptide" sets up turbulence in the port and impedes flow. To minimize this phenomenon, leave as much metal as possible on the floor of the exhaust ports, particularly about 1 inch in from the exhaust manifold mounting flange. This will create a sort of dam which will help prevent the retrograde flow. When the experts modify small block heads for maximum performance, some metal may even be added in this area by brazing.

[elacruze]

It's true.

Think about the wind whipping around the corner of a building-same concept.

How much it hurts power, is only for the flow bench and race track to know.
Hopefully somebody can shed some experienced light on this.

[Dans 68]

Yes, it makes sense. The "dam" they refer to will help to keep the flow laminar out of the exhaust port. If too much material is removed from the port then, as is described, a reverse (turbulent) flow can develop (a riptide is a good description) at the floor of the exhaust ports and adversely affect the flow of the exhaust gases. Just my

Dan

[chargd72]

I completely agree with the concept.  Just wanted to get some feedback from those who may have heard this before or even have first hand experience.

I will be going this route and I'll let everyone know how it turns out.  Thanks for the replies