How can you measure inlet port sizes on a cossie head?

Also, what are the std port sizes? took the inlet manifold off my car today, and the ports look super smooth, unlike other inlet ports i've seen?? This is on a small turbo esc cos head.

ta.

 

Std = 23mm

Measured nearest the valve.

My current head is 26.5mm inlet

 

i guess i cannot measure it with the head in place on the engine???

 

 

I've always understood the inlet PORTs to be measured like this (at the face of the inlet port) :



So you can measure them with the inlet manifold off (as you have done already).

Inlet VALVE measurement would require the head to come off.