Polished exhaust port.

 

An extremely smooth surface might flow less than a slightly rougher surface. Why don't they make smooth golf ***** instead of dimpled?

 

there is a huge difference between an intake port and an exhaust port in terms of how air or spent exhaust gasses flow through each port respectively. Intake port runs cool with air fuel mixture and requires a ruff finish to help with fuel atomisation. Exhaust gasses flow way faster than the intake port dose. The exhaust port also is affected by thermal energy effects. Also thermal heat transfer into the cylinder heads is reduced with the smoother exhaust ports and reflective surface. The next step beyond this is a thermal coating in the exhaust ports..

 

Thanks for that explanation.

 

The slightly rougher surface on an intake port is a bit more effective on a carbureted engine than on an EFI engine. EFI doesnt need much help when discussing fuel atomization. Carbs definitely stand to benefit from a little bit rougher surface. I don't think there's a huge difference either way. But I do think if you're building a carbed engine, leave the intake surface a little rougher. If building an EFI engine, a smoother finish is probably the way to go. Nice looking finish on the port shown here!!