Re-Working Cylinder Heads for Competition with
2.025"/ 1.680"Valves : up to 7500 RPM Capability.

Information is sourced from ‘Performance American Style’ - a publication produced by AMC in 1973.

Fig 1 - Schematic of Combustion Chamber

Fig 2 - Stock Combustion Chamber

Fig 3 - Modified Combustion Chamber

 With Machine Shop Equipment

1. Spotface to top of intake seat with 2.40" OD cutter with 45⁰ x .12" chamfer (2.16" diameter at end of chamfer).
2. Bore a new throat in intake ports 1.815" diameter x .50" deep from spotface.
3. Spotface to top of exhaust seat with 2.06" OD cutter with 45⁰ x .12" chamfer (1.82" diameter at end of chamfer).

Rework Combustion Chamber

Blend spotface with grinder as illustrated. Note thinner walls around valve guides.

1. Grind 45⁰ seat to 1.99" OD.
2. Grind 60⁰ included cone to 1.94" seat ID.
3. Grind 40⁰ included cone so that the 40⁰ and the 60⁰ are of equal length.
4. Grind to blend valve guide boss to .04" from guide holes as illustrated.
5. Do not remove any metal from inlet end of port up to where the turn starts toward the throat, except for casting flaws. Grind at the turn only as required to blend to the throat to 0.10" minimum throat lengths.
6. Remove all sharp edges between cones and at the end of throat with round file and polishing cloth.

Fig 4 - Rework Intake

1. Grind 45⁰ seat to 1.64" OD (1.68" valve) or 1.58" OD (1.62" valve).
2. Grind 60⁰ included angle cone to intersect seat at 1.57" seat ID (1.68" valve)or 1.50" seat ID (1.62" valve).
3. Grind 0.730" throat radius to centre of valve guide for approximately 180⁰ in direction of flow.
4. Blend throat to port.
5. Remove minimum amount of metal necessary to blend end of valve guide to port.

Fig 5 -  Rework Exhaust

 Notes

1. Do not attempt to change shape or size or ports, except where necessary to match manifold. Exhaust manifold port widths are wider than ports for the end of cylinders to provide for matching after thermal growth.
2. Cylinder bores (3.75" diameter) of 290 - 304 engines must be notched for valve clearance of 0.60" minimum.
3. Check valve seat spotfaces for interference with head gasket.

1. Grind 45⁰ face from 0.045’ outside land length.
2. Grind inside edge of face 20⁰ to 1.930" face inside diameter (reference - 0.75" face width).

1. Grind inside edge of face 18⁰ to 1.55" face inside diameter (1.678" valves)