Welcome to the performance dictionary. This is a compilation of terms often used in the automotive performance community and their respective definitions.
Volumetric Effeciency (VE) - This is a term that measure how effeciently your motor injest air through the intake and expells the exhaust gases out the exhaust side. I put this first for a reason. This is a very important term to understand, because most engine modifications effectively change the VE of your motor, and hince why you decreases or increases in torque and power at various rpms. Mathimatically, VE is the percentage of air that the motor injests and expells vs the total volume of air the motor could potentially injest and expell. First the easy part. How much can your motor injest. Lets use the 2.0L FS motor as an example. Its total displacement is 2.0L's, and it has four cylinders, so each cylinder displaces approximately 0.5L's. Now if the motor were 100% effecient at all rpms it would injest 0.5L's of fresh air each cycle then expell it. Unfortunately, a 100% effecient motor is impossible. How effecient your motor actually is unknown, but as a general rule of thumb most dual overhead cam engines have maximum VE's around 85-90%. This actual numbers are not important though. What is important is the VE curve, or a chart of VE vs RPM. You VE curve will have the same trend as your torque curve, as measured on an engine dyno or a wheel dyno. So your peak VE will occur at peak torque. Without changing the displacement of the motor you cannot injest any more air, but you can change the VE of the existing motor. This takes on infinate degrees of modifications, from something as simply as changing the air filter or as complex as reworking the cylinder head with larger valves and ported runners. So we want to change the VE of the motor? Almost all performance modicafications will increase high rpm VE while sacrificing some low rpm VE. Recalling earlier statements, this means that the high rpm torque will increase and low rpm torque will decrease, and where torque increase, so does power. Learn this and understand it, as you will hear this again and again.
Dyno - This is a term that generally refers to automotive dynamometer, but could also refer to an engine dynamometer. A dynamometer is a piece of equipment that is used to measure the power and torque output at the wheel of a car or crankshaft of the motor for an engine dynamometer. Most automotive tuners use an automotive dynamometer, which I will refer to from here on out. Dynos come in a variety of shapes and sizes, but the most popular dyno, is the Dynojet dynamometer. The Dynojet utilizes large drums of known inertia, mass, and circumference. Your car is straped down so that your drive wheels rotate the drums. Based on how fast and how quickly the drums are spun, a computer can calculate the power and torque that your car is creating. The dyno is one of the best tuning tools out there, and is the only way to quantify the actual gains of a particular performance modification. Keep in mind that a dyno measures power and torque at the wheels. This is what is truely important to you anyway, as this is the power and torque that drives your car, but note that between the crankshaft and wheels are the transmission and drive train. Each of these components introduces losses in output due to friction and inertia, so there is typically a 15% loss (for a manual transmission) in torque and power between the crank and the wheels. Automatic transmissions or AWD drive trains incurr greater losses. The costs of running your car on a dyno are not cheap though. A typically session of 2-4 runs, way cost you $75-$100, or shops will rent the dyno for $100-$200 per hour.
Volumetric Effeciency (VE) - This is a term that measure how effeciently your motor injest air through the intake and expells the exhaust gases out the exhaust side. I put this first for a reason. This is a very important term to understand, because most engine modifications effectively change the VE of your motor, and hince why you decreases or increases in torque and power at various rpms. Mathimatically, VE is the percentage of air that the motor injests and expells vs the total volume of air the motor could potentially injest and expell. First the easy part. How much can your motor injest. Lets use the 2.0L FS motor as an example. Its total displacement is 2.0L's, and it has four cylinders, so each cylinder displaces approximately 0.5L's. Now if the motor were 100% effecient at all rpms it would injest 0.5L's of fresh air each cycle then expell it. Unfortunately, a 100% effecient motor is impossible. How effecient your motor actually is unknown, but as a general rule of thumb most dual overhead cam engines have maximum VE's around 85-90%. This actual numbers are not important though. What is important is the VE curve, or a chart of VE vs RPM. You VE curve will have the same trend as your torque curve, as measured on an engine dyno or a wheel dyno. So your peak VE will occur at peak torque. Without changing the displacement of the motor you cannot injest any more air, but you can change the VE of the existing motor. This takes on infinate degrees of modifications, from something as simply as changing the air filter or as complex as reworking the cylinder head with larger valves and ported runners. So we want to change the VE of the motor? Almost all performance modicafications will increase high rpm VE while sacrificing some low rpm VE. Recalling earlier statements, this means that the high rpm torque will increase and low rpm torque will decrease, and where torque increase, so does power. Learn this and understand it, as you will hear this again and again.
Dyno - This is a term that generally refers to automotive dynamometer, but could also refer to an engine dynamometer. A dynamometer is a piece of equipment that is used to measure the power and torque output at the wheel of a car or crankshaft of the motor for an engine dynamometer. Most automotive tuners use an automotive dynamometer, which I will refer to from here on out. Dynos come in a variety of shapes and sizes, but the most popular dyno, is the Dynojet dynamometer. The Dynojet utilizes large drums of known inertia, mass, and circumference. Your car is straped down so that your drive wheels rotate the drums. Based on how fast and how quickly the drums are spun, a computer can calculate the power and torque that your car is creating. The dyno is one of the best tuning tools out there, and is the only way to quantify the actual gains of a particular performance modification. Keep in mind that a dyno measures power and torque at the wheels. This is what is truely important to you anyway, as this is the power and torque that drives your car, but note that between the crankshaft and wheels are the transmission and drive train. Each of these components introduces losses in output due to friction and inertia, so there is typically a 15% loss (for a manual transmission) in torque and power between the crank and the wheels. Automatic transmissions or AWD drive trains incurr greater losses. The costs of running your car on a dyno are not cheap though. A typically session of 2-4 runs, way cost you $75-$100, or shops will rent the dyno for $100-$200 per hour.
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