2+2GT
10 Year Member
Well, in point of fact I did mine with an electric die grinder, before I got the air tool kit.
Anyway, the port right at the surface is pretty restrictive, like a sphincter, smaller than the preceeding portion of the port. Especially 67 and later 289/302 heads. The 351W and 5.0 heads start out better that these.
The gray shaded area in this photo is iron that should be removed- imagine the restriction. The nose-shaped bump down in the port is for the internal type Thermactor, and should be removed back to the original concave floor at either side of the bump. Imagine buying a nice new cam and have your exhaust trying to squeeze past that. The alternate type, with the external air injectors, puts the lump in the upper left corner of the port, which may actually be worse.
Anyway, the port right at the surface is pretty restrictive, like a sphincter, smaller than the preceeding portion of the port. Especially 67 and later 289/302 heads. The 351W and 5.0 heads start out better that these.
The gray shaded area in this photo is iron that should be removed- imagine the restriction. The nose-shaped bump down in the port is for the internal type Thermactor, and should be removed back to the original concave floor at either side of the bump. Imagine buying a nice new cam and have your exhaust trying to squeeze past that. The alternate type, with the external air injectors, puts the lump in the upper left corner of the port, which may actually be worse.