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When installing cams with high lifts and long
durations, a few general observations are worth keeping in mind. Remember
that additional cam duration can produce more usable power but too much
duration may actually hurt overall performance. The problem of poor engine
response begins when too much duration results in lower cylinder compression
pressure (at low RPM) which in turn can reduce low RPM torque and power. Too
much duration in a camshaft is not necessarily a good thing.
- Less than 115 psi: poor low speed response, hard
starting. Pistons and cams well not matched or worn rings, valves.
- 125 to 145 psi: OK for stock or modified street
motors. On the lower end of the best range for a stock motor.
- 145 to 165 psi: OK for modified street motors.
Static pressures in this range will be best for stock street motors.
- 165 to 180 psi: Marginal for large displacement
street motors, possible hard starting, detonation and overheating.
- Over 180 psi: These are high performance numbers. Street
motors over 185 PSI may need compression release.
The above numbers are not absolute but the point is that
static compression is important. Proper matching of cams and compression
ratio
will allow engines to be modified for more performance and still run
smoothly in street engines. |
