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What is Intake & Exhaust Duration?

Intake Duration determines how much time the engine has to take a breath of fresh air/fuel. In general, shorter duration will increase low RPM torque and longer duration will increase high RPM horsepower.

Exhaust Duration has the same effect as intake duration, but the results are more dramatic. The ranges of duration numbers that provide optimal performance for the engine are quite narrow. 

What is Intake & Exhaust Lift?

Intake Lift determines how much area is available for the incoming air/fuel mixture. As intake lift increases, peak torque and mid-high RPM horsepower will increase as long as the other engine settings can sustain more intake volume.

Exhaust Lift determines how much area is available for combustion waste to escape the engine. As exhaust lift increases from an inadequate amount, low RPM torque and peak torque will increase. Once the lift number is greater than the engine package requires, peak torque will drop and high RPM torque will increase slightly.

What is Lobe Separation Angle (LSA)?

The lobe separation angle is the angle in camshaft degrees between the maximum lift points of the intake and exhaust lobes.  It also affects the amount of valve overlap (the brief period of time when both the intake and exhaust valves are open).

The tighter the lobe separation angle, the peakier the power curve will be. It produces peak torque earlier—coming on quicker and stronger (but also falling off quicker).

A wide LSA reduces valve overlap, softens the idle and improves overall drivability.

Supercharged and nitrous race engines typically benefit from a wider LSA because they don’t require as much overlap for exhaust scavenging as does the naturally aspirated engine.

What is Intake Centerline (ICL)?

Intake centerline (ICL) will move the torque curve up or down in the RPM range.  Each crankshaft degree of change will move the torque peak by 100-200 RPM. Larger numbers after top dead center (ATDC) will produce higher RPM. Small amounts can be gained by “fine-tuning” the lobe center.

All GPI cams are tested to determine the best centerline, and it will be very close to optimal for all engine specs.