User Guide

Dyno2000 Advanced Engine Simulation—75
Camshaft Modeling
Seat-to-seat timing method—This timing method measures the valve timing—
relative to piston position—when the valve or lifter has only just begun to rise or has
almost completely returned to the base circle on the closing ramp. Unfortunately,
there are no universal seat-to-seat measuring standards. These are some of the
more common seat-to-seat timing methods:
0.004-inch valve rise for both intake and exhaust
0.006-inch valve rise for both intake and exhaust
0.007-inch open/0.010-close valve rise for both valves
0.010-inch valve rise for both intake and exhaust
0.020-inch LIFTER rise for both intake and exhaust
The timing specs measured using these methods are meant to approximate the
actual valve opening and closing points that occur within the running engine. Be-
cause of this, seat-to-seat valve events are often called the advertised or running
timing. The Dyno2000 needs this information to calculate the beginning and end of
mass flow in the ports and cylinders, a crucial step in the process of determining
cylinder pressures and power output. Because of this, directly entering seat-to-
seat timing specifications will produce the most accurate simulation results.
0.050-inch cam timing—This timing method is widely used by cam manufactur-
ers. 0.050-inch cam timing points are always measured at:
0.050-inch LIFTER rise for both intake and exhaust.
This measurement technique is based on the movement of the cam follower
(lifter) rather than the valve. Since the lifter is rapidly opening or closing at 0.050-
inch lift, this technique provides an accurate “index” for cam-to-crank position, and
Seat-To-Seat Timing Method
Seat-to-seat timing measures the valve
timing—relative to piston position—when
the valve or (more rarely the lifter) has
just begun to rise. Here dial indicators
are positioned on the valvespring
retainers and are measuring
valve rise,
which is the most common technique
used with seat-to-seat timing (0.020-inch
LIFTER rise is a notable exception).
Timing specs measured using these
methods are meant to approximate the
actual valve opening and closing points
that occur within the running engine.
Because of this, seat-to-seat valve
events are often called the advertised or
running timing and will always produce
the most accurate simulations.