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Re-Working Cylinder Heads for Competition

Contributed By: Rod Linnett

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.

With Machine Shop Equipment

  • a. Spotface to top of intake seat with 2.40" OD cutter with 450 x .12" chamfer (2.16" diameter at end of chamfer).
  • b. Bore a new throat in intake ports 1.815" diameter x .50" deep from spotface.
  • c. 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.

Rework Intake Ports

  • a. Grind� 450 seat to 1.99" OD.
  • b. Grind� 600 included cone to 1.94" seat ID.
  • c. Grind� 400 included cone so that the 400 and the 600 are of equal length.
  • d. Grind to blend valve guide boss to .04" from guide holes as illustrated.
  • e. 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.
  • f. Remove all sharp edges between cones and at the end of throat with round file and polishing cloth.

Rework Exhaust Ports

  • a. Grind� 450 seat to 1.64" OD (1.68" valve) or 1.58" OD (1.62" valve).
  • b. Grind� 600 included angle cone to intersect seat at 1.57" seat ID (1.68" valve)or 1.50" seat ID (1.62" valve).
  • c. Grind 0.730" throat radius to centre of valve guide for approximately 1800 in direction of flow.
  • d. Blend throat to port.
  • e. Remove minimum amount of metal necessary to blend end of valve guide to port.


  • a. 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.
  • b. Cylinder bores (3.75" diameter) of 290 - 304 engines must be notched� for valve clearance of 0.60" minimum.
  • c. Check valve seat spotfaces for interference with head gasket.

    Rework Intake Valves

    • a. Grind� 450 face from 0.045' outside land length.
    • b. Grind inside edge of face 200 to 1.930" face inside diameter (reference� - 0.75" face width).

    Rework Exhaust Valves

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

corner corner