Rottler P69 Porting a Lima Head

[andyofcolumbusmerkur]

https://www.youtube.com/watch?v=42T4jxc6cAM

[john keefe]

Very cool, especially considering how long it takes to get even close to that with hand porting the head alone. I wonder if those cut-ridges will get smoothed out with a finer bit/stone. IIRC, though, there's a long-standing debate whether leaving those ridges improve flow by inducing tumbling around the valves for more even entry into the chamber, vs. ultra smooth (e.g., Extrude Honing).

[andyofcolumbusmerkur]

It's suppose to make it flow better, like the dimples on a golf ball.

[andyofcolumbusmerkur]

Sorry that wasn't the video with the dimple finish, this YB head has the dimple finish, like a golf ball.
https://www.youtube.com/watch?v=Sofy4tuvJ5c

[zxr250cc]

Hi all,

I have wondered for a long time why racing motorcycles' body panels and the inside of head intake passages are not dimpled like a golf ball. With the video of the head on you tube at least one of them has come to pass. It is a shame I can't afford a head project like that for my car.

Cheers