P to Z


Pascal:The metric measurement for pressure where 1 Pascal=1 Newton per square metre
PDK: Stands for Porsche Doppelkupplungsgetriebe which is their version of a double clutch transmission similar to the DSG box, twins separated at birth
Pitch: The movement of a car on its suspension in reaction to braking or acceleration
Pneumatic Valves: Valves that are operated by air pressure used in F-1 engines to develop valve timing charts that look like square waves
Pop Off Valve: A pressure limiting valve that bleeeds of excess manifold pressure by popping open once a predetermined pressure is exceeded
Positive Offset: A front suspension design where the axis of the pivoting (for steering) of the front wheels intersects the ground inside the center line of the tyre
Pre-ignition: An abnormal condition during the compression stroke of a petrol engine where hotspots of the combustion chamber ignite the fuel mixture before the desired ignition spark causing a ping noise as the two flame fronts meet
PS: Pferdestärke or PS is the German translation of horsepower or horse strength. 1 PS = 0.986bhp.  
PTFE: Poly Tetra Fluro Ethelyne more commonly called Dupont's trade name of Teflon. Low friction, tough and hard used in some bushing applications in racing. Lexus used it in the first LS400 as a wrapping for their spring seats to keep them silent!
Pulse Tuning: The finer art of engine tuning to use the invisible pressure waves in the flowing intake and exhaust gasses to capture slightly more intake charge than the nominal cylinder capacity


quattro: with a small q is Audi's trade name for its full-time all-wheel drive system
Quad cams: Referring to a V engine's two banks of DOHC


Race Compound: With reference to the tyres tread compound, formualted for max grip but little else
Ram air tuning: Intake tracts that take advantage of the high pressure areas on the body of a speeding vehicle to get positive intake pressure to gain power
Renn Sport: German for Race Sport
Roll: the movement of the car due to the weight transfer to the outer wheels during cornering
Roll bar: see anti-roll bar
Roll Cage: The sturdy set of steel bars bolted or welded into the cabin of a racing car to maintain the survival cell of the race car in the event of a crash. Has the side benefit of improving the rigidity of the chassis significantly
Roll Over Bar: a steel bar or pipe fitted to convertible to prevent the occupants from being crushed if the car should roll over
Rose Joint: A clever arrangement of concentric steel and lubricating metals that prevents movement in one plane but allows free movement in the other two, used in racing but lately in some hard core street going cars too



S-Tronic: Audi's name for Double Clutch Gearbox
Steel Braided Hoses: Also known as aeroquip hoses to replace the rubberized brake hoses. A Teflon tube within a sheath of steel braiding reduces the ballooning effect of high heat and pressure on the brake lines/hoses
Sway Bar: see Anti-Roll bar
Synchromesh: An additional set of conical gears to help sync the incoming gears eliminating the crunching of the gears that needed a deft double de-clutch technique to avoid


Tachometer: A meter to show the engine speed
Targa: A Porsche quick fix for a flexing open chassis by making a hoop connecting the two B-pillars and keeping the rear widscreen. The cross between a coupe and caabrio
Telemetry: The process of obtaining performance data, transferring to a computer (on or off location) and controlling(now banned) of the race vehicle via on board sensors and actuators
Telescopic Damper: A type of damper that allows the reduction in length by thee inner rod plunging into(telescoping) into the body of the damper and vice versa
Thermostat: A device that regulates temperature of the engine cooling system
Throttle Body: A butterfly valve that controls the air intake and hence power output of a petrol driven engine, used to be connected to the accellerator by cable but now mostly by electro-mechanical actuators
Tie Rod: Usually refers to the ball joint connector at the ends of the steering rack
Timing: See ignition timing
Titanium: A rare metal that is both tough and light but expensive
Top Dead Center: A crankshhaft position where the conrod is straight upright and the piston is at its highest point in the bore and usually flush with the deck of the engine block
Torque: The measurement of the twisting force generated at a certain distance(1m or 1ft) from the twisting axis as in Newtons-Metre or pound-foot. Power is related directly to torque and its relationship is the rate at which torque is produced and multiplied by rpm.
Torque Converter: See Viscous coupling. Used almost exclusively in automatic transmissions. The fluid couple transfers torque by a small degree of slip between the plates without actually touching.
Torque Reversal: When one backs off the accelerator the engine no longer produces torque and thus acts like a brake by torque reversal where the torque in the driven wheel is acting in the reverse direction becaust it has to drive a (momentarily)powerless engine.
Torque Vectoring: Once a quirky mechanism is now a serious way of sending torque to the appropriate wheel to increase cornering ability or improve handling stability. see E-Diff.
Torsen Differential: Stands for torque-sensing. A completely mechanical type mechanism via a clever arrangement of worm gears to cause progressive lock-up once velocity differentials are detected.
Torsion Bar: Springs do not need to be coiled up to work, spring action can also be derived by a twist couple in a steel rod.
Torsional Rigidity: The resistance in Newtons required to twist the chassis of a car through one degree.
Traction Control System: An intelligent system using the ABS sensors to detect excessive slip due to surplus power and to electronically curtail the excess to allow th tyres to regain grip.
Transmission: This is the usual reference to the vehicle's gearbox. But it also emcompasses all parts involved in transmitting power to the wheels. See drive line.
Transaxle: A engineering design to place the gearbox in the position of the rear diff, in fact incorporate it to achieve a better static and dynamic weight balance.
Turbocharger: A blow-suck mechanical couple that consists of two turbines on a single shaft with one end placed in the path of a high pressure high flow exhaust gas and the other eng sucking in air and pressurising a chamber downstream. Usially operates in the region of 20-30,000 rpm
Twin Cam: Also see DOHC or double overhead cam.
Twin Turbo: An arrangement of two turbos to feed the engine either together or in sequence with different sized turbos


Undersquare: Used to describe an engine with bore dimension smaller than stroke. Opposite of Oversquare.

Understeer: Describing a handling condition where the front wheels are tracing a larger arc than the rears. In a mild form is the preferred handling characteristic for most passenger cars as it feels stable and safe. Opposite of Oversteer.
Universal Joint/Coupling: A solid mechanical joint that allows significant angular deviation in transferring the torque. Also called the Constant Velocity Joint. Commonly used in FWD cars.


V-engine: A clever arrangement of two banks of cylinders in a V-shape. Examples of Vs are V-twin, V4, V6, V8, V10, V12 and V16
Vacuum Servo: The clever use of the engine partial vacuum to assist in pressurising the braking hydraulic system
Valve: In engine parlance Valve is a device that opens and closes an air passage to let in or let out gasses
Valve Bounce: A condition where the fast moving valve has exceeded its springs ability to keep from bouncing up off its valve seat at high rpm. Loss of power and a metallic high pitched rattle is symptomatic of this.
Valve Lift: The measurement of a valves movement from seat to its furthest point outward. Its important as it actually increases the annular area under the valve for gas flow.
Valve Timing: The precise moment and duration of the opening of intake and exhaust valves.
Variable Turbine Geometry: A mobile vane in the turbocharger to direct the exhaust gasses over the turbine to mazimize its low rpm and high rpm performance in an effort to eliminate turbo lag.
Variable Valve Timing: More correctly called variable cam phasing. The ability to shift the duration of the valve opening earlier or later than its norm increases its effective range and hence efficiency.
VarioCam: Proprietary valve timing and lift mechaism from Porsche.
Viscous Coupling: A fluid coupling that has the ability to transfer torque inversely proportionally to the separation of the plates. Used to actively vary torque transfer in differentials.
VTEC: Honda's proprietary mechanism that varies valve timing and lift
VVTi: Toyota's proprietary mechanism to vary valve timing.


Wankel Engine: Also called the Rotary engine is a masterstroke in engineering. An engine with no valves and just a triangular piston that also houses a reduction gear.
Water Pump: An integral engine mechanism that drives the water/coolant around the engine and radiator to maintain temperature
Watt: A unit measure of power where 1W=1 Nm/sec or a measure of electriv power where 1W= 1v x 1A
Weight Reduction: The favourite catchword for serious tuners. Less weight=greater acceleration, braking and cornering. If there was ever a magic cure for all it has to be lightening.
Weight Transfer: The dynamic shift of the car's weight over the wheels due to the changes of acceleration along the lateral and longitudinal axis.
Wheelbase: The dimension measured from hub center of front and rear wheels
Wishbone Suspension: A clever geometric arrangement of two arms shaped like wishbones to keep the wheel constantly vertical through its suspension travel.

X-Frame: Honda's proprietary design of a frame to achieve high torsional rigidity in its S2000 sports convertible

Yaw: When a car or body moves around the vertical axis of the car's center view from the top as in oversteer


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