[DAVID GAGNARD]

here's my uneducated theory:

On the dual plane with the plenum divider,basically one side of the carb feeds 4 cylinders and the other side feeds the other 4 cylinders.....when you add in the notched plenum divider,it lets thing "equalize" to some degree, allowing all 8 cylinders to pull fuel from both sides of the carb instead of 4 cylinders pulling from 1/2 the carb.......

according to the video results,the one inch spacer basically does the same thing........adding the spacer on a notched plenum divider is the best of both worlds,but if you don't have room for the spacer the notched divider will help....

on a side note,you can get an 3/8's inch thick open gasket to go under the carb if you don't have room for the one inch spacer and that should help out some.......

some years ago I did notch a standard RPM dual plane manifold, the car did idle and run smoother at low rpms and I'm sure it made more power thru the rpm range, but one would only be able to tell on a dyno......

David