David Vizard got me thinking about this because he often emphasizes that the exhaust valve size is crucial for optimizing engine performance. He stated that the exhaust valve should be large enough to ensure that the engine can expel exhaust gases efficiently, but not so large that it compromises the velocity of the flow. He often balances the valve size with the port design and the engine’s intended RPM range to achieve the best performance. He likes formulas, but doesn’t have a formula for this one. So it really coalesces with what Darin Morgan says. I think there’s a lot more to this then meets the eye. A lot of volumemetric thermal dynamics going on.
The other thing that got me thinking about this is how everybody has different methods of porting a head. I wonder how many people really know what the hell they’re doing. One that impressed me last night was on Engine Masters looked at a big block and the head was ported and gained about 100 hp. Just from porting! This was Steve Dulcich motor and he did the porting.