shimniok wroteI've heard that polishing should only be done on the exhaust side. The rough casting on the intake prevents fuel from puddling better than a smooth surface would. I'd be curious to hear others' thoughts.
Also FWIW, playing with desktop dyno, it seems port & polish has the biggest gains above 4500rpm on race motors with big breathing requirements... shrug
Michael
Polishing to a high shine yes, it starts to be a detriment on the intake. You want some roughness that will allow the air/fuel to keep mixing, not a mirror polish. What you need to do is port match (if your racing or looking for big gains) and deburr the intake to keep the air flow unobstructed. Get rid of the casting flash and sharp corners (especially around the valve seals) that will create a vortex (vacuum) but still allow swirling and mixing.
The exhaust side - smooth and polish it. But remember that the engine needs some back pressure to function right. Some shops do not port match the exhaust to help that. Others use a smaller diameter exhaust tube to keep the back pressure up. How much BP depends on the engine and application and I don't know how to figure that.
On the 258 I port matched the intake and just polished the exhaust without changing port size, but the 6 is a lower RPM grunt machine :idea:
A pretty good write up is HERE Kits, abrasives yada, yada, yada can be purchased lots of places like Summit or Jegs.
That help any??
Mudrat
