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  • Performance Terms

    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.
    Bryan Pendleton | LeMons Racing Blog | BPi Flow Stacks | Facebook Anyone?

  • #2
    Continued. . . .

    Intake - This refers to a modification of the air intake plumbing that channels air from the air filter to the throttle body and they often include a new filter. Intakes come in all shapes, sizes and colors, with some being more effective than others. Intakes can and often serve two purposes. One purpose is the free up restrictions often found in the stock intake systems. This improves flow at high rpms, which improves high rpm VE, but typically there is a small sacrifice in low rpm VE, because of the larger larger flow path, air velocities are slower, and this decreases VE. Gains from intakes vary depending on the application, but the gains are often very small (less than 5%). The second purpose some intakes serve is to relocate the position of the filter so that it will draw in ambient temperature air and not hot air that is in the engine bay. A cooler air charge means that the density of the air is higher, or that there is more air per a given volume. With more air entering the engine, more fuel can be injected, which effectively increase the output of the motor.

    Cams/Camshaft - Cams orchestrate the valve train on your car. They dictate when and how much the valves on your car open to allow the motor to injest air. Then they dictate when and how much the valves open to let the exhaust gas escape the engine. Cams are driven by the crankshaft of the motor and are synchronized with the crankshaft via the timing belt or chain (2.0L FS uses a timing belt). Some cars come with a single cam which drives both intake and exhaust valves, and some cars have two seperate cams for opening and closing the intake and exhaust valves. The 2.0L FS is refered to as a dual overhead cam engine (DOHC). Cams have a very significant effect on a engines VE. A change in cams could change a motor from a low rpm torque strong truck engine to a high rpm screaming pocket rocket. Generally, tuners try to find a cam that is aggressive enough for some significant power gains, but mild enough so that the car is still street legal, passes emmissions, and does not reduce drivability too much. A change in cams generally changes the VE of the motor so much, that the fuel maps and ignition maps much be optimized for the motors new VE. The potential for cams is nearly endless, but the more aggressive route you take with the cams, often dictates other expensive modifications to accomodate them.
    Bryan Pendleton | LeMons Racing Blog | BPi Flow Stacks | Facebook Anyone?

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    • #3
      Continued . . . .

      FS Motor - This is a designation code for the DOHC 2.0L motor designed and developed by Mazda in 1993. The 'F' refers to the engine family while the 'S' refers the the generation of the motor. There were ealier 'F' series motors but there is no interchangability between the the 'FS' and older 'F' series engines.
      The ‘FS’ motor was used in the 1993-1997 Ford Probe and Mazda 626 and MX-6. The motor has a 83mm cylinder bore and a stroke of 92mm. In 1999, Mazda offered a destroked version of the 'FS' motor, reducing the stroke to 85mm, effectively reducing the engine displacement to 1.8Ls. This destroked 'F' motor as well as the 2.0L 'FS' can be found in the newer Mazda Proteges, MP3's and Protege5's.
      The aftermarket support for the 2.0L FS motors was very limited, but with the emerging of the newer generation 2.0L FS and 1.8L F from Mazda, the aftermarket has picked up considerably. Keep this in mind when you are looking for performance parts, and many parts are interchangable between the two motors.
      Mazda also designed a 2.0L 'FSZE' motor which was designed and built for the Japanese domestic market, and perhaps other markets, but was not available in the US. The motor ran a slightly higher compression ratio, more aggressive intake camshaft, distributorless ignition, and a "staged" intake manifold to squeeze out over 40% more horsepower. FS owners are often interested in this motor swap, but its has proven to be rather difficult due to ECU incompatibilites. If you are interested in this swap, I would recommend obtaining an entire front clip, rather than just the motor.
      Bryan Pendleton | LeMons Racing Blog | BPi Flow Stacks | Facebook Anyone?

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      • #4
        Naturally Aspirated - Naturally aspirated refers to a combustion engine that is injesting air at atmospheric pressure or in other words, without the aid of a turbocharger or supercharger.

        Tuning - Tuning is a process of altering fuel delievery and ignition timing to optimize performance for a given car, whether it be to achieve maximum horsepower or maximum fuel economy. Tuning is a very generic term that is often used without any understanding as to what it truely means. This confusion can probably stem from the fact that there are many ways to tune a car, and the methods for tuning will depend on the car itself. For instance, a carburated small block Chevy can be tuned with a handfull of springs and a phillips screwdriver for altering carburator calibration and distributor timing calibration, where as a modern fuel injected car would require that the ECU be reprogramed, unless additional electronics are used.

        The degree of tuning necessary for a given car depends on the degree of alteration to the car. A stock car or a car with your basic bolt-on modifications will not need to be tuned to run properly, but as the degree of modifications increases, tuning begins to become a necessity. Just about all stock production cars are tuned for reliability, reduced emmissions and fuel economy, leaving room for small improvement on even a stock car for increasing power. Primarily tuning comes into play when the motor has been radically altered. Modifications that will generally necessitate a tuning are cam changes, cylinder head modifications, bottom-end changes, and force induction. With a highly modified motor, significant gains can be seen from properly tuning the motor.

        In this day and age of fuel injection, there are alot of options that will allow an enthusiast to tune his car, or in our case the 2.0L FS Probe.

        1) ECU Reprogram - You can have the ECU reprogrammed. This is a process of altering the fuel and ignition timing maps that are stored in the "brain" of the car. Unfortunately will most likely require shipping your ECU off to someone else. In order for the to properly tune it to your set up and modification, you need to provide them with as much information as possible. The best data to provide is air-to-fuel ratio data throughout the entire rpm range. This may be an iterative process too, in which you have to send the ECU off a second time for some fine tuning.

        2) Piggy-back Electronics - These electronic devices take on many shapes, sizes and colors, but the basic principle is the same. These devices intercept one or more sensors on your car and alter the signal to give false readings to the ECU of the car. The ECU will in turn alter the fuel delievery and ignition timing based on the altered signal. This is a very effective method for moderate levels of tuning and this gives the user control of the tuning as well. This is a very attractive option for people on a tight budget and are not running a radical motor.

        3) Stand-alone ECU's - These electronics devices also take on my shapes, sizes and colors, giving the customer alot of options to choose from. Basically a stand alone ECU replaces the job of your stock ECU in controlling the motor. This is the ultimate solution as it gives the user full control over the motor, so it can be tuned for any possible configuration. The downside as the cost of these "big-boy toys" can easily cost over a $1000 to as much as $5000 for parts alone. Installation is often tedious and requires a working knowledge of modern cars or be prepared to shell out at hundreds of dollars for installation.
        Last edited by BryanPendleton; April 11, 2005, 06:56 AM.
        Bryan Pendleton | LeMons Racing Blog | BPi Flow Stacks | Facebook Anyone?

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        • #5
          VICS - Variable Inertia Charging System is mazda's design for a duel stage intake manifold on their 4cyl models. It uses a set of butterfly valves in the IM that open about 5200 RPM. When they open, they reveal a resonance chamber inside the manifold that the air passes over, similar to blowing across the top of a bottle to make it whistle. This change in harmonics helps aid the motor during the intake process by optimizing the pressure waves.

          VTCS - Variable Tumble Control System is only used during initial start up in cold conditions. It is another set of butterfly valves in the IM near the head port that close off coving 3/4 of the intake port. The 1/4 that remains uncovered causes the air to tumble as it passes through. This simply helps reduce cold start emissions, by helping the extremely rich, cold start fuel curve atomize better. Once the engine is warm or the throttle is pressed, these valves open fully. The problem is, even when open, they are still an obstruction in the IM and hinder flow.
          Last edited by M.Hicks; June 19, 2008, 05:38 PM.
          Matt Hicks
          Silver 97 2.0 Turbo
          Factory Green ZX6RR
          If you have 1,000 posts and have not donated to PT, you should consider doing so.
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