http://www.hipermath.com/engines/exhaust_valve_size

I learned some things.

The 16v thing might relate to being able adjust overlap because of having separate intake and exhaust cams controlling the valves.
And physical limitations of the combustion pocket.. It is an interesting subject. I need to read more too.

Bigger exhaust valve means slower gas speed. Think about the garden hose, you put your finger over the end to make the water go further.

It's the different temperatures of the gas that means you want different valve sizes.

Hey,
I was just reading through some of the articles in the Tech Wiki and wondered:
Why the intake valve is significantly larger? I understand the principle of a larger intake valve means air for power is more readily available, but take this FIGURATIVE example:
40mm carb throat - 40mm intake throat - 40mm intake valve, but on the opposite end, 40mm header runners - 40mm exhaust throat - 35mm exhaust valve. I know I'm not quite the sharpest pencil, but I thought the pressurized exhaust gasses need the larger valve for a quicker and smoother escape? Even in boost applications, an enormous intake pressure of 2 bar still doesn't have the flow and thermobaric need of the exhaust gasses after a compression ratio of 8.5bar.

And if this works so well, why do DOHC head use symmetrical valves? I'm just reeeaaally curious and I'd love to learn from you gentlemen.

Btw, anyone try symmetrical valves?