The MGA With An Attitude
PORTED CYLINDER HEAD - Cutaway for Inspection - PP-403

The photos on this page have been supplied by
Sean Brown, Oregon, USA,
and are reproduced here with his permission.

Sean ported a cracked cylinder head for demonstration purposes only, then band-sawed the head through the ports so a "before and after" view could be photographed. These photos are often sent to prospective customers as a demonstration of what could be expected from the cylinder-head services.

Cutaway exhaust port before and after porting

In the picture above you can notice removal of some of the exhaust port obstruction at the valve guide area, enlarging of the exhaust port just above the valve seat and continuing higher up, and a fairly high polish for the exhaust port walls.

Cutaway intake port before and after porting

In this picture you can notice smoothing of a few ripples in the port wall, and the duller buff finish for the intake port. Note also how short is the vertical leg of the short side turn, and the smaller radius there. This is worse for the intake port because the intake port is larger bore size, making the floor of the horizontal runner lower.

This is of course a cast iron cylinder head, not the aluminum part referred to in the previous article. It does however serve to show the results of properly applied porting techniques. In PP-401 Sean refers to using abrasives in the range of 36 grit (roughing work) to 80 grit fine finishing work). In PP-402 Sean refers to using 80 grit for the exhaust ports, and 60 grit for the intake ports, and creating a uniform "scratch" finish in the ports, and explains why it is best not to over-polish the intake port walls. In the pictures here you can see the difference in surface finish, with the exhaust port having a very smooth finish and the intake port given a slightly coarser buff finish.

In another off-site article "Porting and Polishing Made Easy", an abrasive manufacturer is recommending the use of 80 grit for the intake runners, and a high polish in the exhaust runners. I wonder if they like to make you work a little harder so they can sell more abrasive tools? Just a thought.

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© 2004 Barney Gaylord -- Copyright and reprint information