1994 - 1995 Corvette ZR-1: Characteristics of A.L. Dunn Cylinder Heads
From Greg Van Deventer, Mercury Marine - October 18, 2000:
"The A.L. Dunn cylinder heads have as cast intake and exhaust ports. All cylinder heads up to that point were from the same mold. The '90 - '92 cylinder heads were as cast, (intake port diameters can be less than 32mm) with exception of bowl tools below the valve seats (kind of bullet shaped), and secondary butterfly valve bores with taper below, then in '93 the intakes were core drilled 33mm and a mill cut on the short side radius at some angle, then bowl tools were used."
"The A.L. Dunn cylinder heads have all of the improvements from '93 incorporated into the casting cores. They have a slight blend on the valve seat."
"On the exhaust side, basically the '90-'92 cylinder heads were cast 52mm wide on the oval outlet port at the gasket surface. On the '93s and up until the A.L. Dunn cylinder heads, the opening was opened up side to side to 57mm wide by a CNC mill."
"The A.L. Dunn cylinder heads had this 57mm dimension incorporated into the casting. That's what I recall about this." Greg Van Deventer