I had several sets of Powre Lynz Toolz made up over the years. First one was just a 20 pitch thread bit made of not very good metal. I chewed it up with my first job -- my brother's 4.0 liter Jeep head for his 258 (4.2 liter) block we rebuilt.
I think round 3 of bits I had 20, 16, and 12 pitch Toolz made. This allowed me to customize the boundary layer and direct the flow of air where I wanted it to go. This jacked up the swirl in the cylinders tremendously. I put the 12 where I didn't want the air to go, and the 20 where I wanted it to go, and used the 16 in the blend zones. This picture shows the worn out original and the first batch of 3.
Another port picture:
Lastly, I applied the screw thread concept to the back sides of the intake valves.
