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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.
Notes
- 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)
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