In August of 1997 Athos Zanzani contacted me on a recommendation from Frank Giannini (sp?) to evaluate the heads of the Motobi 6.

The original had ports that were quite large and I felt the flow could be improved. Athos relayed the results to Primo Zanzani and 2 sets of heads were sent from Italy. One was to be sent to Cosmopolitan Motors and the other back to Zanzanis in Italy when finished.

The first step to improving the airflow required welding the intake and exhaust ports to raise the floors of both ports. The next step was to determine the port cross sections based on information supplied by Zanzanis on how high the engine could be revved. 
I used a 10500 rpm peak and determined the intake port cross sections using a velocity that was higher than 300 fps to produce peak horse power. RHC tends to use higher than average velocities on singles and twin cylinders. This produces a wider power curve with a slight peak horsepower loss.

Next, the intake port was reshaped into an oval port, which gave the straightest shot at the intake valve and also left a wide port floor. This assisted the air movement on the short side radius. 

Both heads were flow tested after completing. The intake and exhaust ports both gained considerable airflow.

The heads were then assembled and returned. Primo installed the new head on the engine and took it to the dynamometer for testing. The results were remarkable! The original heads produced 28 hp and the new with redesigned ports 36 hp out of only 15 cubic inches.

As a result of the gains, Zanzanis had the heads recast with the RHC ports.