PATTAKON
Greece
How much more power
will this system make?
The
above question is the first, and sometimes the only question.
It
comes from famous tuners, it comes from ordinary people, too.
It
confirms that only few people appreciate flat torque, direct response, low
consumption, less emissions etc, while almost everybody is ready to pay a lot
for more power.
So,
can the VVA offer more power and how much?
Let's
see the case of the second prototype.
The
Continuous Variable Valve Actuation is applied on a B16A 1600cc VTEC Honda
engine, which basically means:
·
Substitution of the original "three
pieces" rocker arms with "single piece" light alloy ones. The new rocker arms
are lighter a lot, so reduce the inertia problems, they have roller cam
followers, so reduce the friction at valve train system a lot, and they are
stronger ("one piece" compared to "three basic pieces" interconnected with pins
sliding along relevant holes) so they can operate at higher revs and/or longer
valve lift reliably.
·
Introduction of two control shafts, one
for controlling the exhaust valve lift profile and one for controlling the
intake valve lift profile. They move "slowly" and only when the valve lift has
to be changed. They are mounted on bearings formed on the original aluminum of
the cylinder head, just bellow camshafts.
·
Regrind (re-profile) of the camshafts to
get a desirable valve lift profile and to eliminate the mild cam lobes as well.
·
Substitution of the induction system
(intake manifold, plenum, throttle valve, air filter box and pipes) with four
bell mouths, directly fixed on the cylinder head. The combination of the eight
individual butterflies (i.e. of the eight intake valves) with the four bell
mouths will out-flow the best conventional individual throttle body
combination, it will also out-flow the best plenum / throttle body combination:
the fewer the obstacles in the air path, the freer the breathing.
·
Direct rotation of the control shafts
with the throttle cable coming from the gas pedal.
·
Reprogramming of the Injection / Ignition
controller, with main variables the "revs" and the "intake valve lift".
For
the rest, the VVA engine can be tuned as any other engine (for instance harder
valve springs, titanium valve retainers, increased compression, racing
connecting rods, reinforced block etc).
It
sounds bizarre, but an engine with the VVA can make at least as much power
as the same engine without the VVA can make at most.
The
proof is simple:
Designing
the cam profiles (pure geometry) of the VVA engine to give, for a specific
rotation angle of the control shafts, valve lift profiles identical to the
valve lift profiles used on the original non-VVA engine, what is achieved is a
VVA engine which, at the specific rotation angle of the control shafts, behaves
as the twin brother of the non VVA engine, making the same power.
Then
the rotation of the control shafts at one direction can offer a little wilder
valve lift profiles, for even more power output at high revs, while the
rotation of the control shafts at the other direction offers from less wild to
very mild valve lift profiles for improved operation at medium to low revs and
at partial loads.
More
important than its maximum power output is the ability of the VVA engine to
operate at medium to low revs and at partial loads in a completely different
way than conventional.
In
VVA the "small scale velocity" of the gas, during combustion at medium to low
revs and partial loads, is more or less constant and many times faster than in
conventional engines, changing the efficiency, the drivability and the
emissions a lot.
Today
everybody still asks "how much more power will this system make?".
Tomorrow
the question could change to "OK, your engine makes great peak power, but
beyond peak power what else it makes?"