Bobby,

A plot of data collected from my engine stand with a butterfly valve to restrict the exhaust flow is attached.

The MAP was taken only to about 16” rather than full throttle before starting to close the valve.  I tried to close the valve gradually and opened it rapidly.  The valve didn’t seal perfectly since I couldn’t kill the engine completely, but it was still pretty effective.  The EGT’s didn’t drop until the valve was almost as closed as I could get it and at no time did they rise until the valve was opened. About 22 psi of exhaust gas pressure was developed with the valve closed.

The engine did not run smoothly with the valve closed but there was no popping.  Remember that this is with a 13B with the peripheral exhaust which may behave somewhat differently than a Renesis.

Steve