Definitions of the
terminology used in the Camshaft Specifications Tables is listed below.
Manufacturer is the
recognized manufacture of a specific cam. You may notice as you review these tables that
some cam grinds for different manufactures are identical in every way. Major Manufacturers
like Crane and Andrews make many of the cams sold on the market.
Cam Grind lists the Catalog Number for the
listed cam. Not all the cams listed are currently manufactured.
BTDC means Before Top Dead Center
ABDC means After Bottom Dead Center
BBDC means Before Bottom Dead Center
ATDC means After Top Dead Center
Intake Open BTDC is the number of degrees
before top dead center that the intake valve opens on the exhaust stroke.
Intake Close ABDC is the number of degrees
after bottom dead center that the intake valve closes on the compression stroke.
Exhaust Open BBDC is the number of degrees
before bottom dead center the exhaust valve opens on the power stroke.
Exhaust Close ATDC is the number of degree
after top dead center the exhaust valve closes on the intake stroke.
Intake Duration is the number of degrees the
intake valve stays open as measured at .053 inches of lifter lift.
Exhaust Duration is the number of degrees
the exhaust valve stays open as measured at .053 inches of lifter lift.
Overlap is the number of degree that the
exhaust and intake valves are open at the same time.
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.
LSA is the Lobe Seperation 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 narrow LSA will produce
greater low end torque and a wide 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 to determine how an
increase or decrease in LSA is expected to change the performance of the engine.
Intake Lift is the maximum intake valve lift
in inches.
Exhaust Lift is the maximum exhaust valve
lift in inches.
Intake Lift TDC is the intake lift in inches
at TDC.
Exhaust Lift TDC is the exhaust lift in
inches at TDC.
Low RPM is the published or observed low end
of the recommended usable RPM range. Running an engine below this RPM may not yield good
performance, or worse yet may cause detonation.
High RPM is the published or observed
maximum recommended usable RPM range. Running an engine above this RPM will not yield
addtional horse power.
Bolt In cams can be installed in bikes with
stock heads and stock pistons. Milled heads may change the ability to use a particular cam
in a specific engine. Always check with the cam manufacturer for suitability to your
engine combination. Bolt in cams are indicated with a Y.
Minimum CID is the minimum recommended Cubic
Inches of Displacement for the listed cam. Cams designed for stroker motors may not be
suitable for stock displacement engine. Most cams designed for 80 CID engines will work in
an 88 CID engine. Cams for engines larger than 88 CID should consult with their engine
builder and the cam manufacturer for suitability to your specific application.
Estimated HP Maximum is the observed or a
published maximum horse power output for a specific cam grind. Sources of this information
are various motorcycle magazines, dynometer sheets sent to V-Twin Café by riders and the
Dyno research facilities located at Cycle-Rama
in Pinellas Park, Florida. Your specific engine combinations may not achieving the same
results. The ability of an engine to produce high horsepower is a result of carburation,
intake manifold, port design, valve diameter, cam lift, cam duration, piston design,
ignition timing, compression ratio and a bunch of other variables.
