If you look at enough cams, you might
begin to notice that cams with the same duration and lift can have different performance
characteristics when installed in similar bikes. At first glance, it may seem difficult to
explain. A difference in the lobe separation angles (LSA) of the cams can explain the
difference. Here is a summary of what general conditions you could expect for the engine
if the LSA is made wider or narrower.
||Wide Separation Angle
||Narrow Separation Angle
|Low End Power
|High End Power
LSA is the Lobe Separation Angle or the
number of degrees between the intake and exhaust lobe centerlines. The LSA has a direct
relationship to amount of overlap on a cam. Cams with identical duration and lift
specifications can have very different LSAs. Generally speaking, a wide LSA will produce
greater low end torque and a narrow separation angle will produce better top end power. For
any given LSA, an engine will give similar torque curves and peak torque RPMs even with
different overlaps. Refer to the LSA table above to determine how an increase or decrease
in LSA is expected to change the performance of the engine.
Intake Lobe Centerline is an imaginary line
that passes through the camshaft rotation axis and the point of maximum lift of the intake
lobe. Changing the lobe centerline without changing the duration can increase or decrease
the point at which intake events take place during engines cycles. Increasing the intake
lobe center line from 104 to 106 degrees is considered retarding. All events will take
place later in the engine cycle. Retarding the cam causes the intake valve to open and
close later. This will reduce cylinder pressure which reduce the low speed performance of
the engine. Remember that advancing or retarding a cam effects both the intake and
exhaust. Do not advance or retard a cam by installing the cam with the timing mark offset
by one tooth. One tooth on the timing gear is about 17 degrees.
The cam can be offset by pressing off the timing gear and
re-installing it. This should only be performed by experience performance mechanics or by
the manufacturer. A better solution is to use Crane
Cams High-Roller series of camshafts with an offset keyway timing gear than can be
advanced or retarded 4 degrees.
Exhaust Lobe Centerline is an imaginary line
that passes through the camshaft rotation axis and the point of maximum lift of the
exhaust lobe. Changing the lobe centerline without changing the duration can increase or
decrease the point at which exhaust events take place during engines cycles.