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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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