Lotus 2004 ELISE Service Notes page 113

Lotus Service Notes
Note that compromises are involved in the programming of inlet cam timing, since advancing the valve
opening point also advances the valve closing point, when the ideal might be to advance the opening and retard
the closing points. For any particular engine running conditions, the timing is adjusted to optimise either the
valve opening point and overlap period, or the valve closing point, whichever provides the most benefit.
The range of inlet cam timing available is from:
Opening 33° BTDC, Closing 15° ABDC
to;
Opening 10° ATDC, Closing 58° ABDC
or;
Opening 58° BTDC, Closing 54° ABDC
to;
Opening 15° BTDC, Closing 97° ABDC
Variable Valve Lift
Both inlet and exhaust camshafts are machined with two cams for each cylinder, a low lift cam and a high
lift cam. Each low lift cam actuates, via a low friction roller, a rocker arm which connects with a pair of inlet or
exhaust valves. The corresponding high lift cam actuates a spring loaded tappet housed within the rocker arm,
and under low speed conditions, has no effect on valve operation due to the clearance between the bottom of
the tappet and the rocker arm.
When engine speed reaches 6,000 rpm at normal running temperature, the ECU operates a spool valve
on the back of the cylinder head to close an oil return line, and raise oil pressure within the rocker pivot shaft
and passages within each rocker. This increased oil pressure is sufficient to overcome the spring loading of a
packer pin contained within each rocker arm, which is then forced between the bottom of the high speed cam
tappet and the rocker arm. Each high lift cam then controls valve operation, with the rocker being lifted clear
of the low speed cam. The higher valve lift for both inlet and exhaust valves in conjunction with the variable
valve timing, provides greater efficiency and power output at high engine speeds.
Standard (low speed) valve lift: - inlet; 7.25 mm
High speed valve lift:
Note that engine speed is limited to 6,000 rpm until normal running temperature has been attained.
)
) with standard (low speed) valve lift
)
}
} with high speed valve lift (see below)
}
- exhaust; 7.25 mm
- inlet; 11.4 mm
- exhaust; 10.0 mm
Section EH
Illustrations overleaf...............................
Page 5