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TECHNICAL ARTICLES & PAPERS

Research on Aerodynamic Drag Reduction by Vortex Generators by Masaru Koike, Tsunehisa Nagayoshi, Naoki Hamamoto
Abstract - One of the main causes of aerodynamic drag for sedan vehicles is the separation of flow near the vehicle’s rear end. To delay flow separation, bump-shaped vortex generators are tested for application to the roof end of a sedan. Commonly used on aircraft to prevent flow separation, vortex generators themselves create drag, but they also reduce drag by preventing flow separation at downstream. The overall effect of vortex generators can be calculated by totaling the positive and negative effects. Since this effect depends on the shape and size of vortex generators, those on the vehicle roof are optimized. This paper presents the optimization result, the effect of vortex generators in the flow field and the mechanism by which these effects take place.

PDF Version <<< [Full Technical Paper]

Engine Volumetric Effeciency by Bryan Pendleton
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.

Fundamentals of Brakes by Bryan Pendleton
I often here about the debate between cross-drilled rotors and slotted rotors. To understand the benefits and short comings of these two types of rotors I feel it is first necessary to understand the basics of how your brakes work in the first place. We all know what are vehicle's brake systems are there for, but few understand what they are actually doing. Not from a mechanical level, but from an energy level. The brakes on your car, whether disc brakes or drums accomplish the task of stoping your vehicle by converting the kinetic energy of your moving vehicle into thermal energy or heat. That is the key, that your brakes convert kinetic energy into heat. It is your rotors and surrounding components that are there to absorb this heat and then transfer it to the air so they can convert more kinetic energy into heat.

When does a brake system become inadequate? Answer: When the system cannot effectively transfer enough heat away to operate at "suitable" temperatures. If a brake system is in a situation in which it is "forced" to convert too much kinetic energy to heat, the brake system becomes saturated with heat energy because it is unable to transfer it away fast enough. At these elevated temperatures your brake pads, rotors, or other components can begin to fail from the excessive heat.

So our question now is how do we improve our brake system with just a rotor change. Well the bigger (larger diameter, thicker, etc.) your rotor is the more heat is can absorb without being "over-heated". Larger rotors also inheritly have more surface area for heat to be transfered to the air. This is why you always see high power sports cars with larger disc brakes, or why you find larger vehicle with large brake systems, because the faster or the heavier the vehicle is the more kinetic energy it will have at speed. Without some other major modifications we cannot easily use a larger rotor though. Another option is to improve the rotor's ability to transfer heat to the air, thus improving your braking capacity. This is often found in the form of cooling vanes which are sandwiched between the two rotor surfaces. These cooling vanes add surface area to which heat can be transfered to the air, and promote air flow through the rotor core. So the more cooling vanes you have the marrier. Finally there is the infamous slotted and cross-drilled rotors. Both of which sacrifice rotor mass to provide more effecient transfer of heat to the air. I don't think there is any doubt that cross-drilled rotors are more effective at transfering heat, making them the optimum choice for braking performance, but they do have their disadvantages. Because of the rotor's loss of mass and the addition of the holes you now have a rotor which will have localized high-heat concentrations which cause thermally induced stresses to develop in the rotor which can potentially lead to warped or even cracked rotors. Slotted rotors are similar, but they effectively sacrifice the effeciency of transfering heating by improving the duribility of the rotor. One other phenomenon that both slotted and drilled rotors help eliminate is "gasing" of the pad/rotor interface. Under the extreme tempertures of heavy breaking gases are spent in this interface, which effectively can cause your pads to "float" on the gas layer. Slotted and drilled rotors avoid this by giving the gases a route to escape, much like thread on a tire does for wet driving. So if you are looking for performance my recommendation would be to go with the cross-drilled, but if you are looking for an excellent performing rotor that will give you long life, I would recommend the slotted rotors.

Dyno by Bryan Pendleton
This is a term that generally refers to an 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 wheels 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 drivetrains incurr greater losses. The costs of running your car on a dyno are not cheap. A typically session of 2-4 runs may cost you $75-$100, or shops will commonly rent the dyno for $100-$200 per hour.

MAF Sensor's by Bryan Pendleton
A Mass Air Flow (MAF) Sensor is a very important component of today’s modern day electronic fuel injected (EFI) gasoline engines. The MAF Sensor is used by the engine control module (ECM) to determine the mass of air entering the combustion chamber of the engine. With the mass air flow information, engine speed (rpm) and engine load (throttle position), the ECM can accurately deliver the necessary fuel for complete and efficient combustion (i.e. more power).

A MAF does not directly measure the mass of air entering the combustion chamber, but rather accurately estimates it by taking an indirect measurement from a small sample of the air flow. This is important to note, because if something upstream of the MAF alters the flow characteristics then this will impact the output of the MAF and ultimately the fuel delivery when the ECM is operating in closed-loop. The MAF Sensor utilizes a hot wire filament that could be housed in a separate sample tube or suspended in the main flow path of the intake system. This hot wire filament is heated by passing an electrical current through the filament, but like a light bulb. When air flows across the heated filament, heat is transferred from the filament to the air through convection. As the hot wire filament changes in temperature so does its internal resistance. As the temperature of the filament decreases, the resistance of the filament will also decrease. When the filament resistance decreases, the amount of current flow through the filament will increase. So the more heat that the air flow can transfer from the filament the higher the current will be through the hot wire filament. It’s the measurement of this current that is proportional to the mass of air flowing across the filament. This current is the converted to a voltage signal that is typically on the order of 0-5volts, which is then sent to the ECM for control of the fuel delivery.

It is important to maintain your MAF sensor so that its calibration does not change. Reference the How-To section for more information on how to maintain your MAF sensor to ensure you are getting the maximum performance from you fuel inject car.

Automotive Tuning by Bryan Pendleton
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:

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.

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