Nicks Garage 383 build

Thru the years I’ve had heads come into the shop where the exhaust valves were literally sunk into the head about a 1/4”.
The engines were skipping from cylinders that had nearly zero compression………because the valve had receded into the head far enough to bottom the plunger into the lifter.
When you see the ex valve valve buried down into a hole that deep, you have to realize there is very little flow happening until the valve head clears the chamber roof, which greatly reduces the amount of effective duration available to get rid of the spent gasses.
Not only that, but the new shape of the seat & port can flow way less than they did prior to the seat recession took place.
Basically, the farther the valves sink, the lower the port flow, and you effectively have less exhaust duration.
So, the spent gasses have to go somewhere……..and if they can’t get out of the exhaust port, there’s an intake valve opening up a hole, and they’re gonna shoot right up in there.
Letting spent exhaust gasses up into the intake port is a big time power killer.