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After the cam has been researched, selected and installed, additional time spent on minor adjustments may prove beneficial (although you may end up confirming the original cam position as best for your purpose).
This stage should be repeated after every major change in engine tune (exhaust length, carburetor size, plenum volume, stall speed, axle ratio, &c.).
These remarks are relevant for any single-camshaft engine, including many L6 and V8. They are not advice, but comments which may prove to be of interest if the engine’s performance cannot be sorted out any other way.
Cam advance
Advancing the camshaft (the intake & exhaust valves both open & close earlier) has these general effects:
» cranking pressure (gauge pressure) is increased
» tendency to knock at low speed is increased
» low speed power is increased
» idle speed is increased
» peak torque is increased, but may be at lower RPM
» peak power may be reduced
» intake valve to piston clearance is reduced
» exhaust valve to piston clearance is increased
» traction (for ½ mile, &c. racing) is reduced
» overlap duration is not affected, but engine vacuum may change
» idle and low speed exhaust note is louder, due to both earlier intake closing and exhaust opening
» LSA is not affected
If power continues to go up as the cam is advanced beyond 8°, the cam is probably too large (especially: the intake closing point is too late), or the engine needs more compression.
Cam retard
Retarding the camshaft (the intake & exhaust valves both open & close later) has these general effects:
» cranking pressure is reduced
» tendency to knock at low speed is reduced
» low speed power is reduced
» idle speed is probably reduced
» idle smoothness is increased
» peak torque may be reduced, but at higher RPM
» peak power may be increased
» intake valve to piston clearance increased
» exhaust valve to piston clearance reduced
» traction (for ½ mile, &c. racing) is increased
» overlap duration is not affected, but engine vacuum may change
» idle and low speed exhaust note is softer, due to both later intake closing and exhaust opening
» LSA is not affected
If power continues to go up as the cam is retarded beyond 4°, the cam is probably too small (especially: the overlap is too short, or LSA too wide).
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