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LOWSHO
Glossary of Turbo Terms
Absolute Pressure
This is a measurement of pressure that includes the 14.7 psi of pressure that is always present (at sea level). So the absolute pressure of a car with the turbo set to 10 psi is 24.7.
Air/Fuel Ratio
The air/fuel ratio (AFR) is the amount of fuel by weight compared to the amount of air by weight with in a combustion charge mixture. It is a numeric value that indicates the richness or the leanness within the combustion chambers. Too rich a mixture 10:1 (10 air widgets to one fuel widgets) or richer can rob power and result in poor fuel economy. Too lean, 13:1, can cause harmful detonation with in the combustion area. While 11:1 or 12:1 seems like the proper middle-ground, the engine's static compression ratio, head modifications, fuel quality, amount of boost and resistance to detonation all play a factor in identifying the best target AFR. AFR is THE controlling factor when it comes to tuning. Addition and/or subtraction of fuel as well as timing are made against the backdrop of AFR.
Ambient Temperature
The temperature of the outdoor air. It is usually used to compare to a charge air temperature to determine the cooling efficiency of an intercooler or, perhaps a radiator.
Area/Radius Ratio (A/R)
Is a numeric reflection of the size of a given housing gleaned from an equation that divides the area at a point in the housing by the point's radius as measured from the shaft of the wheel. While compressor housings have A/Rs the measurement is most important on the turbine side of the turbo. The size of the turbine housing will be critical in determining the responsiveness and/or top-end flow of the turbocharger. A responsive unit will have a lower A/R and will spool-up quickly but will sacrifice maximum flow and possibly cause backpressure in the system. Conversely, a big A/R housing will sacrifice responsiveness in order to flow more volume at the top end. The discharge area is a key factor in the A/R equation.
Backpressure
is caused when airflow is restricted in someway causing reversion within the system.
Blow-Off Valve
Some times referred to as bypass valve this device combats compressor surge with in the intake tract of the turbo system. The valve can be vented to atmosphere or re-routed into the turbo system.
Blow-Throw
A type of turbo system where the throttle plate is after the turbocharger. This is the most common arrangement among electronically fuel-injected applications.
Boost
The pressure above atmospheric measured at the intake manifold that is generated by a forced induction device.
Boost-up
A term I am taking credit for coining. It refers to upping the boost pressure from the stock setting with little or no attention to fuel enrichment. There is usually 20 percent more duty cycle left in the injectors of a factory turbo car or there are easy ways to up fuel flow without major modifications. A boost-up cashes in that untapped potential while keeping a focused eye on the AFR. It can be dangerous and should never have taken credit for coining it.
Boost Controller
A device, manual or electronic, plumbed inline with the wastegate that fools the wastegate and allows more than the prescribe boost pressure to be realized. Most controllers can only double the spring rating of the wastegate in use. Electronic controllers can enhance performance by more precisely controlling the pressure as it nears the max setting. An untouched wastegate tends to open earlier and bleed of boost as it nears the maximum. An electronic unit can hold off opening the gate, providing more boost/power for a longer time then opening the wastegate valve very quickly. While the maximum boost remains the same the acceleration curve of the car can be greatly improved.
Boost Threshold
The point, read lowest engine speed, where the turbo makes usable, initial boost (one or two psi). Used to help calculate turbo lag.
Center Section
Also known as the cartridge, the center section of the turbo is the portion of the unit that is between the housings. It provides the cooling for the bearings, usually in the form of oil, that support the common shaft.
Charge Air Density
The amount of oxygen molecules in a given volume of air. A cooler charge contains more air molecules and, consequently, has more power potential. An intercooler takes heated compressed air and cools it, which returns some density and provides an opportunity to make more power.
Cold Side
Refers to the compressor side of the turbo.
Compressor
Also called the cold side of the turbo. It is the shinier housing where the charge air enters to be compressed, or pressurized, before moving through the system and into the engine.
Compressor Efficiency
Refers to the thermodynamic performance of the compressor. The act of compressing air heats it, hence the popularity of intercoolers. An efficient compressor wheel/compressor housing combination will create the least temperature gain. Wheel speed is the issue and there is a range of speeds that provide optimal efficiency in relation to wheel size and housing size. Turn up the boost too much and you risk over-speeding the wheel, causing it to chop at the air as it compresses it. This results in additional heat, a loss of charge density and a corresponding loss of power potential.
Compressor Surge
Picture an engine under full boost and what happens within the turbo system when the driver jumps off the accelerator. The throttle plate closes but there is still boost coming through the system. The air will come to the throttle plate and stack up behind it. The pressure begins to back-track into the system going all the way back to the compressor housing where it encounters the compressor wheel. The wheel is slowed, stopped and/or reversed in direction by the surge of air. A blow-off valve opens to redirect the surge out of the system.
Detonation
Unwanted, spontaneous combustion of the air/fuel mixture usually before the flame front. It occurs when the cylinder pressure and cylinder temperature are such that the mixture combusts on its own; also know as auto-ignition. Detonation can be detected by a ping or knock coming from the engine. The sound is the result of the uncontrolled explosion of the charge air creating a shock wave within the combustion chamber. The wave contacts the piston or the cylinder wall and makes the noise.
Detonation Threshold
The jagged edge of tuning, the detonation threshold is the cross over point where detonation occurs. The goal of a competent tuner is to extend the threshold by adjusting fuel and timing, performing cylinder head mods, enhancing intercooling to facilitate efficiency, lower the heat of the charge air and keep the conditions in the combustion chamber favorable for smooth, controlled combustion. Each engine has its own threshold.
Discharge Area
Refers to the size of the turbine housing where it stops prior to the turbine wheel. The size of this portion of the housing determines the speed in which the exhaust gases contact the turbine wheel and has a great impact on the A/R of the housing.
Draw Through
A turbo system design where the throttle plate is before the turbo. It is common in carbureted set-ups.
Duty Cycle
Sometimes wrongly called Pulse Duration, duty cycle it is the percentage of flow rate of a given fuel injector. At around 95% duty cycle some injectors can experience difficulty, not opening and closing completely, electronic overload etc and their inconsistent performance can wreak havoc during the tuning process. Pulse duration is the time in milliseconds an injector is open, and is a factor in determining duty cycle.
FOD (fawd)
Foreign Object Damage is pretty self-explanatory. It has happened when there are scars, chips, dents or divots on the compressor wheel. FOD is caused by debris getting into the turbo inlet then being chewed on by the compressor wheel blades. In extreme cases the debris can damage the turbo, intercooler and internal engine parts.
Gauge Pressure
The amount of boost in the intake manifold without taking Absolute Pressure into consideration.
Hot Side
Refers to the turbine side of the turbo.
Intended Usage
The goal or expectation of the turbo system based on the usage of the vehicle i.e. street, drag race, road course or quick response versus high horsepower.
Intercooler
A head exchanger designed to cool the intake charge after compression and increase the density of the air going into the engine. The most popular type of intercooler is an air-to-air unit, some racing applications use air-to-liquid designs. The mounting position impacts the performance potential of an air-to-air unit. A front-mount gets cooler air, more air and is physically bigger than other mounting styles. Top mount is the next best type, as seen on the WRX. It sits on top of the engine and is subjected to the heat coming off the engine. A fender mount or side-mount intercooler is the smallest type and is usually tucked away where it gets little airflow across its core.
Intercooler Efficiency
Is determined by taking the temperature reading of the incoming air from the compressor side of the turbo before the intercooler and comparing it to the temperature of the air coming out of the unit.
Lag
Turbo Lag is the time between when the driver hammers the accelerator and when the Boost Threshold is reached. A response turbo is smaller and has less lag than a bigger turbo that takes more time to make noticeable boost.
Lean
A lean engine condition occurs when there is too little fuel (in relationship to air) present in the combustion mixture. See AFR. The condition can lead to Detonation.
Pre Ignition
Pre-Ignition is unwanted, spontaneous combustion of the air/fuel mixture BEFORE the spark plug fires. Consider this auto-ignition in correlation with timing. Ideally combustion occurs at or after top dead center, thrusting the piston through its power stroke. Image the damage when this uncontrolled explosion erupts as the piston is moving up in the cylinder, wherein the explosion tries to force the piston backward on the crank.
Pressure Ratio
The ratio of absolute boost pressure as compared to atmospheric pressure.
Response Turbo
A smaller sized turbo that is designed, or sized, for quicker spool-up. On the road this turbo delivers quick thrust but does so at the cost of top-end power.
Rich
An air/fuel ratio where there is too much fuel in the mixture. A rich condition usually means power is being drowned out and poor fuel economy can be a byproduct of this ailment.
Spool-up
The act of a turbo coming to life. The time it takes to go from a static condition to useable boost, or boost threshold.
Top-End Turbo
A larger sized turbo that is designed, or sized, to create more horsepower by flowing more air at high engine speeds. It makes its big power at the cost of responsiveness.
Turbine
Also called the hot side of the turbo, the turbine uses the exhaust gases coming from the engine to spin the turbine wheel.
Turbocharger
A turbocharger is an exhaust-driven compressor made up of a compressor housing, compressor wheel, center section, turbine housing, turbine wheel, bearings and a common shaft. Exhaust flows into the turbine housing and spins the turbine wheel which is connect by way of a common shaft to the compressor wheel inside the compressor housing. The center section contains the lubrication and cooling orifices and bearing that support the common shaft.
Volumetric Efficiency
Or VE is the amount of the intake charge that is successfully ingested by the engine during the intake stroke compared to the theoretical maximum it can ingest based on the swept volume of the cylinder. VE, measured as a percentage, is a rating of the flow capability of an engine, or more specifically the flow of the cylinder head. Naturally aspirated engines will have a hard time flowing 100%, anything in the 95% and up is considered good. Since a forced-induction engine is pushing air into the cylinder head it often able to generate VEs of well over 100%.
Wastegate
Is a valve that controls the amount of exhaust energy that reached the turbine side of the turbo. It contains a spring that determines the maximum boost pressure. When this point is reach the valve opens and redirect the exhaust gases around the turbine and into the exhaust system downstream of the turbo. The pressure signal sent to the wastegate is what a boost controller alters to trick the gate into allowing a high maximum boost pressure.
Absolute Pressure
This is a measurement of pressure that includes the 14.7 psi of pressure that is always present (at sea level). So the absolute pressure of a car with the turbo set to 10 psi is 24.7.
Air/Fuel Ratio
The air/fuel ratio (AFR) is the amount of fuel by weight compared to the amount of air by weight with in a combustion charge mixture. It is a numeric value that indicates the richness or the leanness within the combustion chambers. Too rich a mixture 10:1 (10 air widgets to one fuel widgets) or richer can rob power and result in poor fuel economy. Too lean, 13:1, can cause harmful detonation with in the combustion area. While 11:1 or 12:1 seems like the proper middle-ground, the engine's static compression ratio, head modifications, fuel quality, amount of boost and resistance to detonation all play a factor in identifying the best target AFR. AFR is THE controlling factor when it comes to tuning. Addition and/or subtraction of fuel as well as timing are made against the backdrop of AFR.
Ambient Temperature
The temperature of the outdoor air. It is usually used to compare to a charge air temperature to determine the cooling efficiency of an intercooler or, perhaps a radiator.
Area/Radius Ratio (A/R)
Is a numeric reflection of the size of a given housing gleaned from an equation that divides the area at a point in the housing by the point's radius as measured from the shaft of the wheel. While compressor housings have A/Rs the measurement is most important on the turbine side of the turbo. The size of the turbine housing will be critical in determining the responsiveness and/or top-end flow of the turbocharger. A responsive unit will have a lower A/R and will spool-up quickly but will sacrifice maximum flow and possibly cause backpressure in the system. Conversely, a big A/R housing will sacrifice responsiveness in order to flow more volume at the top end. The discharge area is a key factor in the A/R equation.
Backpressure
is caused when airflow is restricted in someway causing reversion within the system.
Blow-Off Valve
Some times referred to as bypass valve this device combats compressor surge with in the intake tract of the turbo system. The valve can be vented to atmosphere or re-routed into the turbo system.
Blow-Throw
A type of turbo system where the throttle plate is after the turbocharger. This is the most common arrangement among electronically fuel-injected applications.
Boost
The pressure above atmospheric measured at the intake manifold that is generated by a forced induction device.
Boost-up
A term I am taking credit for coining. It refers to upping the boost pressure from the stock setting with little or no attention to fuel enrichment. There is usually 20 percent more duty cycle left in the injectors of a factory turbo car or there are easy ways to up fuel flow without major modifications. A boost-up cashes in that untapped potential while keeping a focused eye on the AFR. It can be dangerous and should never have taken credit for coining it.
Boost Controller
A device, manual or electronic, plumbed inline with the wastegate that fools the wastegate and allows more than the prescribe boost pressure to be realized. Most controllers can only double the spring rating of the wastegate in use. Electronic controllers can enhance performance by more precisely controlling the pressure as it nears the max setting. An untouched wastegate tends to open earlier and bleed of boost as it nears the maximum. An electronic unit can hold off opening the gate, providing more boost/power for a longer time then opening the wastegate valve very quickly. While the maximum boost remains the same the acceleration curve of the car can be greatly improved.
Boost Threshold
The point, read lowest engine speed, where the turbo makes usable, initial boost (one or two psi). Used to help calculate turbo lag.
Center Section
Also known as the cartridge, the center section of the turbo is the portion of the unit that is between the housings. It provides the cooling for the bearings, usually in the form of oil, that support the common shaft.
Charge Air Density
The amount of oxygen molecules in a given volume of air. A cooler charge contains more air molecules and, consequently, has more power potential. An intercooler takes heated compressed air and cools it, which returns some density and provides an opportunity to make more power.
Cold Side
Refers to the compressor side of the turbo.
Compressor
Also called the cold side of the turbo. It is the shinier housing where the charge air enters to be compressed, or pressurized, before moving through the system and into the engine.
Compressor Efficiency
Refers to the thermodynamic performance of the compressor. The act of compressing air heats it, hence the popularity of intercoolers. An efficient compressor wheel/compressor housing combination will create the least temperature gain. Wheel speed is the issue and there is a range of speeds that provide optimal efficiency in relation to wheel size and housing size. Turn up the boost too much and you risk over-speeding the wheel, causing it to chop at the air as it compresses it. This results in additional heat, a loss of charge density and a corresponding loss of power potential.
Compressor Surge
Picture an engine under full boost and what happens within the turbo system when the driver jumps off the accelerator. The throttle plate closes but there is still boost coming through the system. The air will come to the throttle plate and stack up behind it. The pressure begins to back-track into the system going all the way back to the compressor housing where it encounters the compressor wheel. The wheel is slowed, stopped and/or reversed in direction by the surge of air. A blow-off valve opens to redirect the surge out of the system.
Detonation
Unwanted, spontaneous combustion of the air/fuel mixture usually before the flame front. It occurs when the cylinder pressure and cylinder temperature are such that the mixture combusts on its own; also know as auto-ignition. Detonation can be detected by a ping or knock coming from the engine. The sound is the result of the uncontrolled explosion of the charge air creating a shock wave within the combustion chamber. The wave contacts the piston or the cylinder wall and makes the noise.
Detonation Threshold
The jagged edge of tuning, the detonation threshold is the cross over point where detonation occurs. The goal of a competent tuner is to extend the threshold by adjusting fuel and timing, performing cylinder head mods, enhancing intercooling to facilitate efficiency, lower the heat of the charge air and keep the conditions in the combustion chamber favorable for smooth, controlled combustion. Each engine has its own threshold.
Discharge Area
Refers to the size of the turbine housing where it stops prior to the turbine wheel. The size of this portion of the housing determines the speed in which the exhaust gases contact the turbine wheel and has a great impact on the A/R of the housing.
Draw Through
A turbo system design where the throttle plate is before the turbo. It is common in carbureted set-ups.
Duty Cycle
Sometimes wrongly called Pulse Duration, duty cycle it is the percentage of flow rate of a given fuel injector. At around 95% duty cycle some injectors can experience difficulty, not opening and closing completely, electronic overload etc and their inconsistent performance can wreak havoc during the tuning process. Pulse duration is the time in milliseconds an injector is open, and is a factor in determining duty cycle.
FOD (fawd)
Foreign Object Damage is pretty self-explanatory. It has happened when there are scars, chips, dents or divots on the compressor wheel. FOD is caused by debris getting into the turbo inlet then being chewed on by the compressor wheel blades. In extreme cases the debris can damage the turbo, intercooler and internal engine parts.
Gauge Pressure
The amount of boost in the intake manifold without taking Absolute Pressure into consideration.
Hot Side
Refers to the turbine side of the turbo.
Intended Usage
The goal or expectation of the turbo system based on the usage of the vehicle i.e. street, drag race, road course or quick response versus high horsepower.
Intercooler
A head exchanger designed to cool the intake charge after compression and increase the density of the air going into the engine. The most popular type of intercooler is an air-to-air unit, some racing applications use air-to-liquid designs. The mounting position impacts the performance potential of an air-to-air unit. A front-mount gets cooler air, more air and is physically bigger than other mounting styles. Top mount is the next best type, as seen on the WRX. It sits on top of the engine and is subjected to the heat coming off the engine. A fender mount or side-mount intercooler is the smallest type and is usually tucked away where it gets little airflow across its core.
Intercooler Efficiency
Is determined by taking the temperature reading of the incoming air from the compressor side of the turbo before the intercooler and comparing it to the temperature of the air coming out of the unit.
Lag
Turbo Lag is the time between when the driver hammers the accelerator and when the Boost Threshold is reached. A response turbo is smaller and has less lag than a bigger turbo that takes more time to make noticeable boost.
Lean
A lean engine condition occurs when there is too little fuel (in relationship to air) present in the combustion mixture. See AFR. The condition can lead to Detonation.
Pre Ignition
Pre-Ignition is unwanted, spontaneous combustion of the air/fuel mixture BEFORE the spark plug fires. Consider this auto-ignition in correlation with timing. Ideally combustion occurs at or after top dead center, thrusting the piston through its power stroke. Image the damage when this uncontrolled explosion erupts as the piston is moving up in the cylinder, wherein the explosion tries to force the piston backward on the crank.
Pressure Ratio
The ratio of absolute boost pressure as compared to atmospheric pressure.
Response Turbo
A smaller sized turbo that is designed, or sized, for quicker spool-up. On the road this turbo delivers quick thrust but does so at the cost of top-end power.
Rich
An air/fuel ratio where there is too much fuel in the mixture. A rich condition usually means power is being drowned out and poor fuel economy can be a byproduct of this ailment.
Spool-up
The act of a turbo coming to life. The time it takes to go from a static condition to useable boost, or boost threshold.
Top-End Turbo
A larger sized turbo that is designed, or sized, to create more horsepower by flowing more air at high engine speeds. It makes its big power at the cost of responsiveness.
Turbine
Also called the hot side of the turbo, the turbine uses the exhaust gases coming from the engine to spin the turbine wheel.
Turbocharger
A turbocharger is an exhaust-driven compressor made up of a compressor housing, compressor wheel, center section, turbine housing, turbine wheel, bearings and a common shaft. Exhaust flows into the turbine housing and spins the turbine wheel which is connect by way of a common shaft to the compressor wheel inside the compressor housing. The center section contains the lubrication and cooling orifices and bearing that support the common shaft.
Volumetric Efficiency
Or VE is the amount of the intake charge that is successfully ingested by the engine during the intake stroke compared to the theoretical maximum it can ingest based on the swept volume of the cylinder. VE, measured as a percentage, is a rating of the flow capability of an engine, or more specifically the flow of the cylinder head. Naturally aspirated engines will have a hard time flowing 100%, anything in the 95% and up is considered good. Since a forced-induction engine is pushing air into the cylinder head it often able to generate VEs of well over 100%.
Wastegate
Is a valve that controls the amount of exhaust energy that reached the turbine side of the turbo. It contains a spring that determines the maximum boost pressure. When this point is reach the valve opens and redirect the exhaust gases around the turbine and into the exhaust system downstream of the turbo. The pressure signal sent to the wastegate is what a boost controller alters to trick the gate into allowing a high maximum boost pressure.
amen . cats=*****:laugh_ti:
also one thing to keep in mind when talking about the turbo SHO's when comparing them to s/c SHO's is that, almost all supercharched cars have one of 2 or 3 configurations. yea they have a few minor differences and there are some one off setups, but for the most part it's one or two designs. When it comes to the Turbo cars, there is not one single car that is even remotely close to another(minus NCtaurusSHO's two cars). because everything has had to be custom made.
