[Steve C.]

I had a set of 1969 #16 d-port heads that had welded-in modifications for swirl developed by Pete McCarthy many years ago. Apparently he only did a few chambers with it and was experimenting, some mention of it was featured in High Performance Pontiac magazine. I later sold them to Paul Knippen and today there is question if it was a big factor in their performance.

From early issues of High Performance Pontiac magazine about 32 years ago and Pete McCarthy's articles about head porting...

He talks about the most important element of port shape, and it's effect on the airflow direction into the chamber, commonly called "swirl". He stated if the qualities of high air volume are combined with high air velocity and rapid swirl, combustion efficiency can be enhanced.

BUT, it's not just about port shape only. He also noted how high-swirl technology can require that the shape of the combustion chamber to complement the port shape. A twisting, rotating fuel mixture will scatter quickly unless the chamber is shaped to accommodate the momentum of the air mass as it exits the port. He goes further to briefly discuss how he reshaped a combustion chamber roof to enhance combustion swirl efficiency.

And the article includes a picture how he reshaped the combustion chamber in the area around the intake valve to promote this swirl effect. Unfortunately I no longer have pictures of my chambers with the swirl modification.


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