AFR Blue Hornet Mopar cylinder head, Charles Servedio

The manifold being attached is effectively plugging off an area of the port, which is allowing the air to stay attached at the SSR to a slightly higher lift, which is how the gain is realized.

Years ago, I was porting some Indy 360-1’s that nosed over at high lifts.
If I just stuck my finger across the bottom of the radius inlet entry it would calm the port/SSR right down.
I had the customer send the intake to me, and as I remember it, the flow at higher lifts(after the point where the SSR was giving up) was higher with the manifold on vs off.

My .02 about the 5th cut is…….. for the application the heads will be used on, it was a step backwards.