Turbo and tuning wiki A-D

This is a wiki or lexicon for technical words and common abbreviations in the automotive industry

Turbocharger and Tuning Wiki A-D

A

A/F

Air/ fuel ratio

The stoichiometric mixture for a gasoline engine is the best ratio of air to fuel, that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is 14.7:1 i.e. for every gram of fuel, 14.7 grams of air are required.

A/R

A/R (Area/Radius) is a term used to define a geometric characteristic of all turbine and compressor housings.

A/R Ratio

The square area of the turbine housing throat at the tongue divided by the radius from the axis of turbine wheel rotation to the centroid or dynamic center of flow through the volute."

ABDC

When a piston travels the length of its stroke in regular operation, it has reached the bottom dead center when it is at the lowest position in the cylinder, closest to the crankshaft. The piston's point where it is starting to travel back up on its stroke is called after bottom dead center.

Absolute Pressure

Atmospheric pressure at sea level (14.7 psi) with no other pressure applied. An absolute pressure gauge (psia for psi absolute) reads the ambient pressure at the location where the measurement is being taken. If you apply 5 pounds of boost to an absolute pressure gauge at sea level it reads 19.7 psi. In contrast, gauge pressure is a direct pressure reading on a gauge that reads zero at any local pressure until you apply additional pressure boost. It is noted as psig for psi gauge. Most automotive gauges read gauge pressure.

Acceleration

The rate of increase in speed or velocity of an object. - Acceleration is the rate of change of velocity. Usually, acceleration means the speed is changing, but not always. When an object moves in a circular path at a constant speed, it is still accelerating, because the direction of its velocity is changing.

AFR

Rated Air/Fuel ratio at max power - In naturally aspirated engines powered by octane, maximum power is frequently reached at AFRs ranging from 12.5 to 13.3:1 or λ of 0.850 to 0.901. The air-fuel ratio of 12:1 is considered the maximum output ratio, whereas the air-fuel ratio of 16:1 is regarded as the maximum fuel economy ratio.

After Bottom Dead Center (ABDC)

Position where the piston is accelerating away from bottom dead center (BDC). Intake valve closing occurs in this area. (See ABDC).

The dead center is the position of a piston in which it is either farthest from, or nearest to, the crankshaft. The former is known as Top Dead Centre (TDC), while the latter is known as Bottom Dead Centre (BDC).

After Top Dead Center (ATDC)

Piston position where the piston has passed top dead center (TDC) and is accelerating away from it. The exhaust closing event usually occurs in this area. The dead center is the position of a piston in which it is either farthest from, or nearest to, the crankshaft. The former is known as Top Dead Centre (TDC), while the latter is known as Bottom Dead Centre (BDC).

Aftermarket

Aftermarket vs. Original Equipment Manufacturer (OEM)

An OEM refers to something made specifically for the original product, while the aftermarket refers to equipment made by another company that a consumer may use as a replacement."

Air Density

The mass per unit volume of the earth’s atmosphere at a given location. Air density is inversely proportional to altitude, or density decreases with increasing altitude. Therefore air density is reduced at higher elevations.

Air/ Fuel Ratio

The ratio of air mixed with fuel for the purpose of combustion in an internal combustion engine. The ideal ratio for best power usually falls between 12.8: 1 and 13.5: 1. That is 12.8 parts air to 1 part fuel. With excess fuel, the mixture is rich (12.1: 1 or less). If there is excess air, the mixture is lean (15.1: 1 or higher). (See stoichiometric ratio.)

Ambient Conditions

This refers to current local conditions in terms of temperature and pressure. A sample of ambient conditions for any given day might include the current temperature, atmospheric pressure (barometer), humidity, and water vapor pressure.

ATDC

After top dead center

Atmospheric Pressure

Current Barometric pressure. The normal air pressure at sea level. ie (14.7 psi or 1.0 bar at sea level). 14.68 pounds per square inch at sea level with a barometer of 29.92 Hg and 60-degree air with no humidity.

B

bar

Metric pressure unit - The bar is a widely used metric unit of measurement for pressure, and 1 bar equals precisely 100,000 pascals. Even though bar is not an SI unit, it has been adopted as one of the most popular pressure units, particularly in European countries. In Europe, most pressure measurement instruments are specified with pressure ranges in bar.

Base Circle

The round portion of a camshaft lobe where no motion is imparted to the valve lifter. When a lifter is on the base circle of the cam, there is zero lift.

BBDC

Before bottom dead center

BDC

Bottom dead center

Bearing Housings

Cast iron housing, the centre of the turbo that houses the turbine piston ring seal, the journal bearing(s) and the thrust bearing, which are all fed with pressurised oil from the engine.

Before Bottom Dead Center (BBDC)

Piston position before reaching bottom dead center. Normal area for exhaust opening event.

Before Top Dead Center (BTDC)

Piston position (typically number-1) before or approaching top dead center. The piston is decelerating and the intake valve opening normally occurs in this area.

bhp

Brake Horsepower (bhp) Horsepower as calculated from observed torque on an engine dyno.

More about horse power at Wikipedia.

https://en.wikipedia.org/wiki/Horsepower

BMEP

Mean cylinder pressure calculated from observed torque on an engine dyno.

BMEP

Brake mean effective pressure - The term BMEP is an engineering term that means Brake Mean Effective Pressure. Mean is another word for average, which in this case means average effective pressure of all stroke cycles. This is used to evaluate all engines, whether they are Two or Four Cycle. BMEP is a function of temperature of the gases in the cylinder. To increase the temperature, you need to burn more fuel, thus making more heat. Or another way is to make better use of the existing fuel. Torque is a function of BMEP and displacement only. HP is a function of torque and rpm.

Bob Weight

An adjustable weight temporarily attached to a crankshaft to simulate the mass of the piston, rings, rod, and bearings for the purpose of balancing the crankshaft.

Boost

Boost and Bars Boost is the increase in manifold pressure supplied by either a supercharger or a turbocharger. One bar of boost is equal to 14.504 psi or 1 atmosphere. A 1-bar MAP sensor reads vacuum only. A 2-bar MAP sensor reads pressure above atmospheric up to 15 psi. A 3-bar sensor reads up to 30 psi above atmospheric. These are all absolute pressure sensors. Hence, a 3-bar sensor reads ambient atmospheric pressure plus up to 30-psi boost. You need a 2-or 3-bar MAP sensor to read boost pressure.

Bore

Area of of the top part of a engine piston - In a piston engine, the bore (or cylinder bore) is the diameter of each cylinder. Engine displacement is calculated based on bore, stroke length, and the number of cylinders.

Bore diameter

The circular diameter of an engine’s cylinders. Cylinder bore diameter is the measurement across the inside of the bore. It can be listed in either inches or millimeters.

Bore Spacing

The distance between centerlines of adjacent cylinder bores.

Bore spacing is the distance from the centerline of one cylinder bore to that of the adjacent cylinder. Assuming the bores are perfectly round, this distance can be determined by measuring the distance from one cylinder wall edge to the far cylinder wall of the adjacent cylinder.

Bore/Stroke Ratio

An engine’s bore dimension divided by its stroke length. If the bore is larger the engine is said to be over-square. If the bore is smaller, the engine is under-square. Square and over-square engines are typically more efficient due to superior breathing characteristics.

BorgWarner

BorgWarner Inc. is one of the big turbo manufactures. BW has a large number of different products for the automotive industry

Bottom Dead Center (BDC)

The point where a piston is at the absolute bottom of its travel in a cylinder bore."

Brake Mean Effective Pressure (BMEP)

Mean cylinder pressure calculated from observed torque on an engine dyno.

BS

Bore spacing. Bore spacing is the distance from the center line of one cylinder bore to that of the adjacent cylinder. Assuming the bores are perfectly round, this distance can be determined by measuring the distance from one cylinder wall edge to the far cylinder wall of the adjacent cylinder.

BSFC

Brake Specific Fuel Consumption (BSFC) Pounds of fuel burned per hour divided by horsepower. It is not an indicator of rich or lean, but rather a measure of engine efficiency. Highly efficient performance and racing engines often generate a BSFC of 0.35 to 0.42, much less than 1/ 2 pound of fuel per horsepower per hour. Production engines are now approaching these values as automakers improve efficiency. The general rule for sizing fuel injectors is 0.50 lbs/ hr for gasoline. Most super-charged and turbocharged engines require 0.55 to 0.60 for best performance under boost.

BTE

Brake Thermal Efficiency.

Brake Thermal Efficiency is defined as break power of a heat engine as a function of the thermal input from the fuel. It is used to evaluate how well an engine converts the heat from fuel to mechanical energy.

BTDC

Before top dead center

Burn Rate

The flame propagation speed of the combustion process. It is determined by the hydrocarbon components in the fuel and is not related to octane which is a measure of resistance to detonation. Fast burning fuels are required for best power in modern high speed engines.

C

c/s

Cross-sectional area. The cross-sectional area of a cylinder is equal to the area of a circle if cut parallel to the circular base. The cross-sectional area is the area of a two-dimensional shape that is obtained when a three-dimensional object - such as a cylinder - is sliced perpendicular to some specified axis at a point.

CAF

Corrected Air Flow. Corrected Flow is the mass flow that would pass through a device (e.g. compressor, bypass duct, etc.) if the inlet pressure and temperature corresponded to ambient conditions at Sea Level, on a Standard Day (e.g. 101.325 kPa, 288.15 K).

Cam Lobe

The eccentric portion of a camshaft that opens the valves by raising the valve lifters. In essence, the cam lobe is a device that converts rotary motion into linear motion.

CC

CC represents the unit “Cubic Centimeter” of Volume. And in case of Engines it is used to represent the Volume of the Internal Combustion Engine Cylinders.

The CC can also be represented in Liters.

1000cc = 1000 cm³ = 1 Liter = 1.0L

cc/min

Cubic Centimeters per minute or cc per minute

Center-to-Center Length

The distance between the centerline of the piston pin bore and the crank pin bore of a connecting rod.

Centroid

The dynamic center of exhaust gas flow through the volute of the turbine housing. Not usually the dimensional center, but typically biased toward the outer half. The point where half of the gas flow is above the center and half of it is below the center.

CFM

Cubic Feet per Minute.

As used in the automotive context, CFM, or cubic feet per minute, refers to the quantity of air and fuel the fuel delivery system can provide an engine through the intake manifold.

Charge

A reference to the fuel/ air mixture that enters the cylinder for combustion, i.e., the incoming charge.

Charge Speed

The speed of the intake charge in feet per second. Also known as port velocity.

Chevy engine - Gen I

First-generation Chevy small-block.

The first generation of Chevrolet small-blocks began with the 1955 Chevrolet 265 cu in V8 offered in the Corvette and Bel Air.

Chevy engine - Gen II

Second-generation Chevy small-block (LT1). The Generation II engine is largely an improved version of the Generation I, having many interchangeable parts and dimensions.

Chevy engine - Gen III

Third-generation Chevy small-block (LS series). Chevrolet introduced the automotive world to the LS engine with the ... The LS1 was the first mill from GM's Gen III small-block engine platform.

Choke Line

Indicates the flow limit and is located on the right side of a compressor map.

CHRA

(Centre Housing Rotating Assembly). The CHRA is essentially a turbocharger minus the compressor and turbine housings. It incorporates the complete rotating assembly, shaft & wheel, bearing housing and compressor wheel.

ci

Cubic inch

cid

Cubic inch displacement

Compression Ratio

The ratio between a cylinder’s swept volume at BDC and its final combustion volume when the piston is at TDC. Typical compression ratios range from 8: 1 to 11: 1.

Compressor

Compressor Wheels

Radial multi-bladed compressor in a turbocharger that draws in ambient filtered air, compresses it within housing, and then blows it out into the intake of the engine.

Corrected Air Flow

Firstly, in order to plot the airflow data on a compressor map, you must ensure the flow is corrected to account for differences that affect air density, such as atmospheric conditions.

CR

Compression ratio

CR

Crevice Volume

The small open space between the piston and the cylinder wall above the top piston ring. Need for correct CR calculations

CR: V1

Cylinder volume - Components of CR formula (total combustion space). When calculating compression ratio (CR), several volumes are added or taken into account for the CR-formula, ie V1, V2, Vn ...

CR: V2

Components of CR formula (total combustion space) : When calculating compression ratio (CR), several volumes that make up fot the total cylinder volume are added or taken into account for the CR-formula, ie V1, V2, Vn ...

Crank

Engine axel

Crank Angle

The crankshaft angle in relation to the piston top position (or pin centerline) in the bore for any given point in the stroke.

Crank Pin

The connecting rod throw on a crankshaft. This is typically called the rod journal.

Crevice Volume

The small open space between the piston and the cylinder wall above the top piston ring.

Cubic Inch

A three-dimensional space whose length, width, and height of 1 inch define its volume. One cubic inch equals 16.387 cubic centimeters and 1 cubic foot equals 1,728 cubic inches.

Cylinder Head

A separate engine component containing the combustion chambers, valves, spark plugs, intake and exhaust ports, and valve gear.

D

DA

Density altitude

Deck Height

The distance the piston top is above or below the deck surface of the cylinder block when the piston is at TDC. If the piston top is below the deck surface it is called positive deck height. If it is above the deck surface it is called negative deck height.

Degree Wheel

A graduated (in degrees) aluminum disk or wheel temporarily attached to the front of a crankshaft to indicate crank position (in degrees) relative to piston position and valve event.

Density Altitude

The density of local air compared to known altitude conditions for standard atmospheric conditions based on air temperature, pressure, and water content.

Density Ratio

The ratio of oxygen content or air density of compressed air relative to the same volume at ambient pressure.

Desired Wheel Horsepower:

Desired wheel horsepower.Input the desired wheel horsepower.

Detonation

The auto-ignition of the fuel mixture prior to the spark event. Caused by high cylinder pressure, unstable mixture quality, excessive localized heat, or a combination thereof. Often called pinging due to the annoying sound.

Diesel

displ

Displacement

The swept volume of an engine’s cylinders measured in cubic inches, cubic centimeters, or liters."

Displacement Ratio

Cylinder volume divided by combustion space volume. It is always 1 less than the compression ratio. Most often used to help calculate the correct amount of cylinder head milling to increase compression ratio.

DL

Drivetrain loss

Dome Volume

The volume in cubic centimeters displaced by a dome on top of the piston. The dome is used to raise the compression ratio by reducing the combustion space above the piston.