A/R A/R
describes a geometric property of all compressor and turbine
housings. Increasing compressor A/R optimizes the performance for
low boost applications. Changing turbine A/R has many effects. By
going to a larger turbine A/R, the turbo comes up on boost at a
higher engine speed, the flow capacity of the turbine is increased
and less flow is wastegated, there is less engine backpressure, and
engine volumetric efficiency is increased resulting in more overall
power.
CHRA - center
housing rotating assembly The CHRA
includes a complete turbocharger minus the compressor and turbine
housings.
Clipped
Turbine Wheels When an angle is
machined on the turbine wheel exducer (outlet side), the wheel is
said to be ‘clipped’. Clipping causes a minor increase in the
wheel’s flow capability, however, it dramatically lowers the turbo
efficiency. This reduction causes the turbo to come up on boost at a
later engine speed (increased turbo lag). High performance
applications should never use a clipped turbine wheel. All Garrett
GT turbos use modern unclipped turbine wheels.
Free-Float A free floating turbocharger
has no wastegate device. This turbocharger can’t control its own
boost levels. For performance applications, the user must install an
external wastegate.
GT The GT designation refers to
Garrett’s state-of-the-art turbocharger line. All GT turbos use
modern compressor and turbine aerodynamics which represent huge
efficiency improvements over the old T2, T3, T3/T4, T04 products.
The net result is increased durability, higher boost, and more
engine power over the older product line.
On-Center Turbine Housings On-center
turbine housings refer to an outdated style of turbine housing with
a centered turbine inlet pad. The inlet pad is centered on the
turbo’s axis of rotation instead of being tangentially located.
Using an on-center housing will significantly lower the turbine’s
efficiency. This results in increased turbo lag, more backpressure,
lower engine volumetric efficiency, and less overall engine power.
No Garrett OEM’s use on-center housings.
Trim Trim is an area ratio
used to describe both turbine and compressor wheels. Trim is
calculated using the inducer and exducer diameters. As trim is
increased, the wheel can support more air/gas flow. Use these
formulas when calculating trim:
Wastegated A wastegated turbocharger
includes an integral device to limit turbo boost. This consists of a
pneumatic actuator connected to a valve assembly mounted inside the
turbine housing. By connecting the pneumatic actuator to boost
pressure, the turbo is able to limit its maximum boost output. The
net result is increased durability, quicker time to boost, and
adjustability of boost.
