T.D.C.
Top
Dead
Center. The position
in
which the piston
has
reached the top of its
travel.
A line drawn between the crankshaft rotational axis, through the connecting
rod
end
axis and the piston pin center would be a straight line. Ignition and valve timing
are
stated
in
terms of degrees before
or
after
TDC.
Thermal Efficiency Regarding engines, the percent of total heat generated which
is
converted into
useful
power.
T.l.T.
Turbine Inlet Temperature. The measurement of
E.G.T.
at the turbocharger turbine inlet.
Torque Twisting moment, or leverage, stated
in
pounds -foot (or pounds -inch).
Turbocharger A device used to supply increased amounts of air to an engine induction system.
In
operation, a turbine
is
driven
by
engine exhaust gas. In turn, the turbine directly drives
a compressor which pumps air into the engine intake.
Turbo Supercharged A term
used
to describe
an
engine which obtains induction air
by
drawing it directly
(Engine) from the atmosphere into the Turbocharger Compression Inlet, compressing the air and
routing it to the pressurized induction system.
Vapor Lock
Variable Pressure
Controller
Vernatherm
Valve
Viscosity
Volatility
Volumetric
Efficiency
Wastegate
Valve
A condition
in
which the proper flow of a liquid through a system
is
disturbed by the
formation of vapor. Any liquid will turn to vapor if heated sufficiently.
The
amount of
heat required for vaporization will depend
on
the pressure exerted on the liquid.
A device used to control the speed, and thus the output of
the turbocharger. It does so
by
operating the wastegate which diverts, more or
less,
exhaust gas over the turbine.
A thermostatic valve used to divert oil through or around the
oil
cooler,
as
necessary,
to maintain
oil
temperature within desired limits.
The
characteristic of a liquid
to
resist flowing. Regarding oil, high viscosity refers to
thicker or "heavier"
oil
while low viscosity
oil
is thinner. Relative viscosity
is
indicated
by the specified "weight" of the oil such as
30
"weight" or
50
"weight". Some oils
are
specified
as
multiple-viscosity such as 1
OW30.
In such cases, this oil is more stable and
resists the tendency to thin when heated
or
thicken when it becomes cold.
The
tendency
of
a liquid to vaporize.
The
ability
of
an
engine to fill its cylinders with air compared to their capacity for air
under static conditions. A "naturally aspirated" engine will always have a volumetric
efficiency of slightly less than
100%,
whereas superchargers permit volumetric
efficiencies
in
excess of
100%.
A
unit,
used
on
the turbocharged engines, to divert exhaust gas through or around the
turbine,
as
necessary, to maintain turbine speed.
As
more air
is
demanded
by
the
engine, due to throttle operation, the compressor must work harder.
In
order to
maintain compressor and turbine speed, more exhaust must flow through the turbine.
The
wastegate valve closes and causes
gas,
which would go directly overboard, to
pass
through the turbine. The wastegate
is
usually operated by
an
actuator which
gets necessary signals from the turbocharger controller.
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