We flowed the head and then they had it extrude honed, it looked pretty but flowed worse. Kind of like a river washing the wrong bank during a flood. It screwed the short side radius. The competition was about the engineering of the vehicle, not really how fast it went so it still did well in the competition. My only experience with extrude honing.
https://www.sae.org/attend/student-events/about-formula The “supersonic blow down” event in an exhaust manifold
is so different than
the “liquid with suspended solids” flow of Exude Hone
that your result is certainly believable.
On Larry Widmer’s old Honda message board my fuzzy memory is that he once wrote
“I have had good results porting exhaust manifolds, but when I quote the price no one want’s to pay”
Widmer and his aero engineer father certainly understood supersonic flow better than most.
