Little Big Chief - Part I: Basic Machining - Pontiac Tech

The No. 17 cylinder heads were taken apart, cleaned, and put back together with test springs for flow bench analysis. Baseline readings were taken, along with an examination of the port, to determine where flow deficiencies were located. Often a shop such as RaceKrafters will "map" the port using velocity probes connected to a manometer (reads inches of water) to see the air movement.

Combustion chamber volume was confirmed and eventually adjusted to provide the desired compression ratio of 9.01:1. The static compression ratio is a function of the piston design, piston-to-deck clearance, and the combustion chamber volume.

With the flow work completed, the deck of the cylinder head was machined for flatness and to adjust the combustion chamber to 80 cc's.

Bob Wise meticulously contoured the airflow path of the cylinder head. The bowls were fully massaged to the roof of the port and the guide boss was streamlined. The short turn was blended and rolled back, and the exhaust radius was blended.

The cast-iron integral valve guides proved to be worn, so a bronze insert was installed in each.

Once the bronze inserts were installed, a special reamer was employed to provide the proper valve stem-to-guide clearance, which is 0.0015. (This photo is for explanation purposes only, as this head is not the No. 17.) Though the No. 17 had press-in studs, RaceKrafters upgraded it to screw-ins during the rebuilding process.

With the guides back to specification and the cylinder head porting complete, a dedicated head shop machine was used to accurately cut the valve angles into the seat. This tool references from the valve guide so that dimension must be exact before the angles can be cut. It's the modern method of producing the valve angles on the seat and is far superior to using grinding stones. The intake seats were cut at 30, 45, 60, 75 and 82 degrees. The exhaust seats were machined for 30, 45, and 56 degrees and to a 4mm radius.

The final machining procedure was to cut the angles on both the intake (45-degree seat, 30-degree back-cut) and exhaust (45-degree seat) valves. This was done with a grinding stone on a special valve-cutting machine. The valve sizes were upgraded to stainless steel 2.02/1.66 inches from 1.96/1.66 and were supplied by Manley.