A pair of new camshafts were
designed and manufactured to substitute the original ones. The new camshafts
are power oriented (high valve lift with increased duration and overlap), while
the VVA guarantees the good operation at idling, partial loads and low to
medium revs.
In the “Reliability Drive”
video the ECU (PGM-FI) unit is not yet reprogrammed, the throttle valve is
active and the valve lift is controlled manually / continuously.
The Assembly.exe (1.8 Mb) shows, in 12 photos, the assembly of
the cylinder head, it also shows the current ValveLift versus CrankAngle plot
(the two red curves are the original high rpm valve lift in comparison).
In the “On the Road, 9000 rpm” video (in QT format, 4 Mb) the
throttle valve is fixed (secured) wide open .
The immovable throttle valve cancels any enrichment of the mixture during
acceleration, without any notice from driver (because the pressure in the
intake manifold is actually constant).
The original MAP (Manifold Absolute Pressure) sensor is replaced by a Valve
Lift Sensor. This sensor is nothing more than a variable resistor (rheostat)
displaceable by the control lever. The stabilized voltage (5 volts) supplied to
the MAP sensor is now applied at the ends of the variable resistor. From the
intermediate movable output of the variable resistor, and according the
rotation of the control lever (which displaces both control shafts), a voltage
signal from 0.45 to 2.9 volts is fed to the ECU replacing the original signal
from the MAP sensor. So the basic maps of injection and ignition are now based
on rpm and on valve lift. The ECU feels just a voltage, no matter it comes from
the original MAP sensor or from the Valve Lift Sensor. The values of the injection
and ignition maps differ a lot compared to the original ones.
The relation of intake and exhaust valve lifts
is not yet optimised.
The engine is controlled by the lift of the
valves. The driver presses the gas pedal, and the gas pedal – through a cable
(string) – displaces the two control shaft increasing the valve lift. The pedal
is hard to press. The response is more than direct.
The engine idles (for the moment) at 460 rpm.
The rev limiter is set (for the moment) at 9.000 rpm.
The VTEC point has no meaning, any more. It is set to 4000 rpm and at these
revs the only that happens is the transfer from the low rpm injection /
ignition maps to the high rpm ones. The increase of the oil pressure for the
activation of the high rpm cam lobes has no effect (just some more oil on the
pivot shafts for the lubrication of the rocker arms).
Valve lifts / Valve springs
The maximum valve lift for the intake valves is 12 mm and for the exhaust
valves is 11 mm.
For the intake valves, each original main intake valve spring is grinded at its
ends to reduce its length for 1 mm. Note that the slightly softer (due to its
reduced length) intake valve spring has to restore a significantly lighter
valve assembly (the rocker arm is less than half the weight of the original
rocker arm assembly).
For the exhaust valves they are used the original double intake valve springs.
Combustion Duration and Conditions
At low revs and partial loads the
combustion duration seems to be as theory says: several times shorter than in
conventional engine.
The spark advance used in the VVA at low to medium revs and at partial loads is
reduced (compared to conventional) remarkably, confirming the fast combustion.
In the VVA the spark happens only a few degrees
BTDC and the combustion process finishes only a few degrees ATDC, so the
mixture feels totally different conditions in comparison to the conventional
where the spark happens at much lower compression and the combustion proceeds
slowly and finishes many degrees after TDC. This is the key point and makes the
difference.
The fast combustion offers many advantages
like: immediate cold start, smooth idling at lower revs, lean burn (air / fuel
ratios of 15:1 to 19:1 or more), clean exhaust, improved economy in town
traffic, etc, etc.