Exhaust valve back side radius

[dhidaka]

What is the influence the backside radius of exhaust valves on flow/performance/HP-torque? Try 10* nail head and 20* tulip and 26* tulip. For example a 2-valve hemi with 60* exit turn and 45* seats. I assumed the default would be some sort of tulip, but the new PipeMax shows many really Hi-Po engines using 12* nail head.

[Newold1]

My favorite setup is a 35 degree back cut on a 24 degree tulip backside on the exhaust valve with a radius as the bottom cut of the the exhaust seat. No radius on the backside of the valve. Really seems to make great lower lift flows on the exhaust side.
I only sbc's, LS's and bbc's, so I won't comment on other heads.