Q

R

R/S or R/L

Rod length to stroke ratio

Repair Kits

Minor – includes just the basic components;

Major – includes all the components needed for a full repair of a turbo; Universal Kits – includes each variation to accommodate for where there are several variations of a model. For instance: Flat or superback compressors wheels, straight or slender shafts etc.

Reversion

The consequential movement of air/ fuel mixture or residual exhaust products back into the port from where it came as a result of piston motion, or a pressure differential caused by valve opening and closing events during overlap when both valves are open at the same time.

Rocker Arm Ratio

A ratio by which the rocker arm multiplies camshaft lift to increase total valve lift.

Rotating Weight

The amount of rotating crankshaft weight that resists rotating motion.

RPM

Revolve Per Minute

rpm

Revolutions per minute (engine speed)

RR

Rocker ratio rpm: revolutions per minute (engine speed)

S

s

second

SAE

Society of Automotive Engineers

Saturation Point

The point at which the intake valve curtain area or flow window matches or exceeds the smallest flow area in the runner, causing the port to become the restriction instead of the valve.

Seal Plates

The component, usually made from aluminium, has a bore housing the compressor end piston ring seal that runs in the groove of the oil flinger or thrust collar. However, on some models, this component doubles up as being the supporting flange that the compressor housing fixes to.

Sensor psia

Absolute pressure

Shaft & Wheels

The complete assembly that describes the turbine wheel and shaft as one component – (Also referred to as a ‘Turbine Wheel’). It uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump.

Shaft Nuts

Holds the compressor wheel and other rotor group parts onto the shaft. This normally has a left hand thread on modern turbos, this high precision machined nut has to be tightened to a specific torque.

Shrouding

A design configuration where inlet and/ or exhaust flow is partially restricted by the proximity of an adjacent combustion chamber wall or the actual cylinder wall. It affects the efficient flow of gases in and out of the combustion chamber.

Siamesed Bore

A block casting configuration where solid material is cast between the cylinders with no space for a cooling jacket. A design intended to increase cylinder wall strength.

Standard Temperature and Pressure (STP)

Atmospheric conditions of 29.92 Hg barometer with 60-degree (F) dry air. This is the standard correction factor used for most performance industry and magazine dyno testing. It results in corrected numbers approximately 4 percent higher than the SAE standard.

STP

Standard temperature and pressure

Stroke

The length of the movement of the piston inside an engine

Supercharger

A belt-driven device that forces air into an engine to increase its breathing capacity and horsepower output.

Swept Volume

The volumetric space swept by a piston top as it travels up and down in the bore.

T

Target Maximum Boost

Maximum boost pressure (Psi)

TDC

Top dead center

Thrust Bearings

A single flat bearing that supports the positive and negative axial loads generated when the turbo rotor accelerates and decelerates. The bearing is fixed and the thrust collar runs within it. A pressurised oil film separates the ramped faces of the bearing from the journal surfaces of the collar.

Thrust Collar

The half of a complete thrust collar that runs on the underside of the thrust bearing. The thrust collar is sometimes in two pieces for applications like a 360 degree thrust bearing.

Thrust Flingers

Located on the turbine shaft. This sits through the hole in the seal plate and acts as a separator/seal between the thrust bearing, seal plate and compressor wheel.

Thrust Washer

Fits between the journal bearing and thrust bearing, acting as a cushion to prevent the parts form touching.

TMB

Target Maximum Boost (psi)

TMIC

Top Mounted Intercooler

Tongue

The beginning of the inner opening in the volute where incoming exhaust gasses are first exposed to the turbine wheel.

Torque

A twisting force expressed in ft-lbs or in Newton-meters for metric applications.

Torque Plate

A thick metal bar with properly spaced bore holes that is bolted to the cylinder block deck surface to simulate the distortion of cylinder head bolts during cylinder honing.

TQ

Torque

Trim

The relation between the inducer and exducer. Trim is given or can be calculated for the compressor and the turbine individually.

Turbine

Turbine

Turbine Housing Area

The area in inches of the turbine housing throat at the end of the tongue perpendicular to the direction of exhaust gas flow.

Turbocharger

An exhaust driven air compressor device that forces air into an engine to increase VE and thus horsepower output.

U

V

Valve Curtain Area

The circular flow window that opens when an intake valve is lifted off its seat by the camshaft.

Valve Lift

Distance the valve is lifted off its seat by the camshaft and valvetrain.

Valvetrain Geometry

A precise relationship between the rocker arm tip and the valve stem that provides optimum lift with minimal side thrusting and wear.

Variable

A mathematical component that can assume any assigned value for the purpose of computation.

VE

Volumetric Efficiency (VE) The ratio of an engine’s actual airflow to its potential or calculated air capacity.

Volumetric Efficiency (VE)

Volumetric Efficiency (VE) The ratio of an engine’s actual airflow to its potential or calculated air capacity.

Volute

The scroll-shaped passage in the cast iron turbine wheel housing. It begins at the flange or foot and follows a decreasing circular path to the turbine wheel."

W

WHP

WHP= wheel horse power

WOT

Wide open throttle

X

Y

Z

λ

λ

Lambda - λ