Johnson Lifters
ARP Catalog

Effects Of Changes in Cam Timing and Lobe Separation Angle

Comp Cams logoThe following tables provided by COMP Cams illustrate how variations in lobe separation angle and cam timing affect engine behavior. Engine builders can refer to these characteristics often to determine the likely effect of any cam timing alterations they may contemplate. Knowing how these things affect engine operation can help you in the engine planning stages if you want to leave some tuning leeway in your cam selection. Our thanks to Comp Cams for providing this easy to use reference guide for our readers.


Advancing Retarding
Begins Intake Event Sooner Delays Intake Closing Event
Opens Intake Valve Earlier Keeps Intake Valve Open Longer
Builds More Low-End Torque Builds More High-RPM Power
Decreases Piston-Intake Valve Clearance Increases Piston-Intake Valve Clearance
Increases Piston-Exhaust Valve Clearance Decreases Piston-Exhaust Valve Clearance


Tighten (smaller LSA number) Widen (larger LSA number)
Moves Torque to Lower RPM Raise Torque to Higher RPM
Increases Maximum Torque Reduces Maximum Torque
Narrow Power band Broadens Power Band
Builds Higher Cylinder Pressure Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock Decrease Chance of Engine Knock
Increase Cranking Compression Decrease Cranking Compression
Increase Effective Compression Decrease Effective Compression
Idle Vacuum is Reduced Idle Vacuum is Increased
Idle Quality Suffers Idle Quality Improves
Open Valve-Overlap Increases Open Valve-Overlap Decreases
Closed Valve-Overlap Increases Closed Valve-Overlap Decreases
Natural EGR Effect Increases Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance Increases Piston-to-Valve Clearance


1) Max Lift or Nose Lobe Separation Diagram
2) Flank
3) Opening Clearance Ramp
4) Closing Clearance Ramp
5) Base Circle
6) Exhaust Opening Timing Figure
7) Exhaust Closing Timing Figure
8) Intake Opening Timing Figure
9) Intake Closing Timing Figure
10) Intake to Exhaust Lobe Separation


Mitech Racing Zone 5 – ROS, NoF (275x 125)
Conley Engines Zone 5 – ROS  (275 x 125)
Summit – Zone 5 -ROS (275 x 125)
CarTech Books – Zone 5 – ROS, NoF (275 x 125)