Turbochargers, which
are essentially air pumps, compress and force more air into each cylinder to
increase an engine’s efficiency and overall output. By fitting more air into the
engine's chambers and making the air-fuel mixture more combustible, it creates
more horsepower and torque when the piston is forced downward by the resulting
explosion. Turbochargers significantly increase an engine’s
torque and horsepower without tremendously increasing its weight, which normally
means an increase in the power-to-weight ratio of your vehicle. Turbochargers
are mounted to the exhaust manifold of an engine in order to utilize the
“wasted” flow of exhaust energy to produce additional power.
Normal atmospheric pressure at sea level is 14.7 p.s.i., but most turbo systems
can deliver at least and additional 6-7 p.s.i. to each cylinder, netting a
40-50% increase in performance. Some racing systems that run
20-30 p.s.i. of boost pressure can even increase horsepower output by as much as
200% or more.
Turbochargers
usually consist of several components; an exhaust gas-driven turbine and a
radial air compressor mounted at opposite ends of a common shaft and enclosed in
cast housings. The shaft itself is enclosed and supported by a center housing,
to which the compressor and turbine housings are attached.
The
turbine section consists of a turbine wheel, a wheel heat shroud and a turbine
housing, with the exhaust gas inlet at the outer diameter of the turbine
housing. Exhaust gases flow inward, past the wheel blades, and exit at the
center of the housing's diameter. Expanded engine exhaust gas is directed
through the exhaust manifold into the turbine housing. The exhaust gas pressure
and the heat energy extracted from the gas causes the turbine wheel to rotate
which drives the compressor wheel.
The compressor
section is composed of a cast compressor wheel, a backplate, and a compressor
housing, with the inlet at the center of the compressor housing diameter. It is
a centrifugal, or radial-outflow device in that the air flows outward, past the
wheel blades, and exits at the outer diameter of the housing. The rotating
compressor wheel draws ambient air through the engine's air filtration system.
Its blades accelerate and expel the air into the compressor housing where it is
compressed and directed through ducting to the engine intake
manifold.
In the case of the
Center Housing and Rotating Assembly (CHRA), the center housing (bearing
housing) supports the compressor and turbine wheel shaft in a carefully designed
bearing system. The bearing system, designed for high speed, does not see heavy
loading as with crankshaft bearings. It must delicately position the wheels as
closely as possible to the contour of the end housings. Key to the positioning
is the oil filling the clearances between the center housing bore, bearings, and
shaft. This oil filled clearance is vital to a turbocharger's efficiency and
longevity.
Exhaust
Control Devices like swing valves, poppet valves, and wastegates help control
turbine speed (which in turn helps to control boost) by releasing excess exhaust
pressure from the turbine housing. They can be an integral part of the turbine
housing or mounted remotely. They are activated either by diaphragms or
cylinders and pistons filled with air or oil. When opened, excess exhaust
pressure is released from the turbine housing, directed to the exhaust system
and expelled into the atmosphere.
Each engine size and power output must
be properly performance matched by the turbocharger. Power output needs
determine the amount of air pressure required to deliver the proper volume of
air to the engine. This is accomplished through combinations of wheel size,
wheel speed and turbine housings. All HKS turbochargers are
blueprinted, balanced and VSR tested at our state-of-the-art manufacturing
facility in Japan to ensure you get the best built and top performing
aftermarket turbocharger available.  |
