1. Follow your league’s rules about race car design to the letter as you try to make your car more aerodynamic. The trend in professional racing is toward a limited number of templates that make sure racing skills remain more important than technology.
2. Lower the riding height of your race car to increase aerodynamics. A race car with a low profile allows wind to pass easily over the hood instead of traveling underneath the body.
3. Install an elongated air dam to your race car’s front fender as an aerodynamic measure. An air dam is a curved piece of plastic that serves a dual purpose: first, it blocks air passage beneath your car, and second, it creates a natural air flow over your hood.
4. Smooth out your fenders as a step toward a more aerodynamic race car. Your fenders should wrap tightly around the front and rear sides of your car, without excess material off the side, to cut down on wind resistance.
5. Play around with the size and shape of your car’s tire wells to find an aerodynamic design. A well-designed car has most of the open space in a tire well on the front side of the tire for maximum air passage.
6. Press down the pillars that form the borders of your car’s doors and windows to decrease drag. These pillars can be reshaped by a mechanic to have a smooth rather than angled appearance without much work.
7. Adjust the settings of your race car’s suspension system, carburator and other parts as you make aerodynamic changes. Young drivers and mechanics make the mistake of changing the car body without thinking about strain on mechanical performance.
8. Run a few laps in your race car to test out changes in aerodynamic design. Use a stop watch to measure improvements in lap speed as motivation for additional changes.

Drag

A simple definition of aerodynamics is the study of the flow of air around and through a vehicle, primarily if it is in motion. To understand this flow, you can visualize a car moving through the air. As we all know, it takes some energy to move the car through the air, and this energy is used to overcome a force called Drag.

Drag, in vehicle aerodynamics, is comprised primarily of two forces. Frontal pressure is caused by the air attempting to flow around the front of the car. As millions of air molecules approach the front grill of the car, they begin to compress, and in doing so raise the air pressure in front of the car. At the same time, the air molecules traveling along the sides of the car are at atmospheric pressure, a lower pressure compared to the molecules at the front of the car.

Just like an air tank, if the valve to the lower pressure atmosphere outside the tank is opened, the air molecules will naturally flow to the lower pressure area, eventually equalizing the pressure inside and outside the tank. The same rules apply to cars. The compressed molecules of air naturally seek a way out of the high pressure zone in front of the car, and they find it around the sides, top and bottom of the car. See the diagram below.

Rear vacuum (a non-technical term, but very descriptive) is caused by the “hole” left in the air as the car passes through it. To visualize this, imagine a bus driving down a road. The blocky shape of the bus punches a big hole in the air, with the air rushing around the body, as mentioned above. At speeds above a crawl, the space directly behind the bus is “empty” or like a vacuum. This empty area is a result of the air molecules not being able to fill the hole as quickly as the bus can make it. The air molecules attempt to fill in to this area, but the bus is always one step ahead, and as a result, a continuous vacuum sucks in the opposite direction of the bus. This inability to fill the hole left by the bus is technically called Flow detachment. See the diagram below.

Flow detachment applies only to the “rear vacuum” portion of the drag equation, and it is really about giving the air molecules time to follow the contours of a car’s bodywork, and to fill the hole left by the vehicle, it’s tires, it’s suspension and protrusions (ie. mirrors, roll bars). If you have witnessed the Le Mans race cars, you will have seen how the tails of these cars tend to extend well back of the rear wheels, and narrow when viewed from the side or top. This extra bodywork allows the air molecules to converge back into the vacuum smoothly along the body into the hole left by the car’s cockpit, and front area, instead of having to suddenly fill a large empty space.

The reason keeping flow attachment is so important is that the force created by the vacuum far exceeds that created by frontal pressure, and this can be attributed to the Turbulence created by the detachment.

Turbulence generally affects the “rear vacuum” portion of the drag equation, but if we look at a protrusion from the race car such as a mirror, we see a compounding effect. For instance, the air flow detaches from the flat side of the mirror, which of course faces toward the back of the car. The turbulence created by this detachment can then affect the air flow to parts of the car which lie behind the mirror. Intake ducts, for instance, function best when the air entering them flows smoothly. Therefore, the entire length of the car really needs to be optimized (within reason) to provide the least amount of turbulence at high speed. See diagram below (Light green indicates a vacuum-type area behind mirror):

Lift (or Down force)

One term very often heard in race car circles is Down force. Down force is the same as the lift experienced by airplane wings, only it acts to press down, instead of lifting up. Every object traveling through air creates either a lifting or down force situation. Race cars, of course use things like inverted wings to force the car down onto the track, increasing traction. The average street car however tends to create lift. This is because the car body shape itself generates a low pressure area above itself.

How does a car generate this low pressure area? According to Bernoulli, the man who defined the basic rules of fluid dynamics, for a given volume of air, the higher the speed the air molecules are traveling, the lower the pressure becomes. Likewise, for a given volume of air, the lower the speed of the air molecules, the higher the pressure becomes. This of course only applies to air in motion across a still body, or to a vehicle in motion, moving through still air.

When we discussed Frontal Pressure, above, we said that the air pressure was high as the air rammed into the front grill of the car. What is really happening is that the air slows down as it approaches the front of the car, and as a result more molecules are packed into a smaller space. Once the air Stagnates at the point in front of the car, it seeks a lower pressure area, such as the sides, top and bottom of the car.

Now, as the air flows over the hood of the car, it’s loses pressure, but when it reaches the windscreen, it again comes up against a barrier, and briefly reaches a higher pressure. The lower pressure area above the hood of the car creates a small lifting force that acts upon the area of the hood (Sort of like trying to suck the hood off the car). The higher pressure area in front of the windscreen creates a small (or not so small) down force. This is akin to pressing down on the windshield.

Where most road cars get into trouble is the fact that there is a large surface area on top of the car’s roof. As the higher pressure air in front of the wind screen travels over the windscreen, it accelerates, causing the pressure to drop. This lower pressure literally lifts on the car’s roof as the air passes over it. Worse still, once the air makes it’s way to the rear window, the notch created by the window dropping down to the trunk leaves a vacuum, or low pressure space that the air is not able to fill properly. The flow is said to detach and the resulting lower pressure creates lift that then acts upon the surface area of the trunk. This can be seen in old 1950’s racing sedans, where the driver would feel the car becoming “light” in the rear when traveling at high speeds. See the diagram below.

Not to be forgotten, the underside of the car is also responsible for creating lift or down force. If a car’s front end is lower than the rear end, then the widening gap between the underside and the road creates a vacuum, or low pressure area, and therefore “suction” that equates to down force. The lower front of the car effectively restricts the air flow under the car. See the diagram below.

So, as you can see, the airflow over a car is filled with high and low pressure areas, the sum of which indicate that the car body either naturally creates lift or down force.

Drag Coefficient

The shape of a car, as the aerodynamic theory above suggests, is largely responsible for how much drag the car has. Ideally, the car body should:

• Have a small grill, to minimize frontal pressure.
• Have minimal ground clearance below the grill, to minimize air flow under the car.
• Have a steeply raked windshield to avoid pressure build up in front.
• Have a “Fastback” style rear window and deck, to permit the air flow to stay attached.
• Have a converging “Tail” to keep the air flow attached.
• Have a slightly raked underside, to create low pressure under the car, in concert with the fact that the minimal ground clearance mentioned above allows even less air flow under the car.

If it sounds like we’ve just described a sports car, you’re right. In truth though, to be ideal, a car body would be shaped like a tear drop, as even the best sports cars experience some flow detachment. However, tear drop shapes are not conducive to the area where a car operates, and that is close to the ground. Airplanes don’t have this limitation, and therefore teardrop shapes work.

What all these “ideal” attributes stack up to is called the Drag coefficient (Cd). The best road cars today manage a Cd of about 0.28. Formula 1 cars, with their wings and open wheels (a massive drag component) manage a minimum of about 0.75.

If we consider that a flat plate has a Cd of about 1.0, an F1 car really seems inefficient, but what an F1 car lacks in aerodynamic drag efficiency, it makes up for in down force and horsepower.

Frontal Area

Drag coefficient, by itself is only useful in determining how “Slippery” a vehicle is. To understand the full picture, we need to take into account the frontal area of the vehicle. One of those new aerodynamic semi-trailer trucks may have a relatively low Cd, but when looked at directly from the front of the truck, you realize just how big the Frontal Area really is.

It is by combining the Cd with the Frontal area that we arrive at the actual drag induced by the vehicle.

Aerodynamic Devices

Scoops

Scoops, or positive pressure intakes, are useful when high volume air flow is desirable and almost every type of race car makes use of these devices. They work on the principle that the air flow compresses inside an “air box”, when subjected to a constant flow of air. The air box has an opening that permits an adequate volume of air to enter, and the expanding air box itself slows the air flow to increase the pressure inside the box. See the diagram below:

NACA Ducts

NACA stands for “National Advisory Committee for Aeronautics”. NACA is one of the predecessors of NASA. In the early days of aircraft design, NACA would mathematically define airfoils (example: NACA 071) and publish them in references, from which aircraft manufacturers would get specific applications

The purpose of a NACA duct is to increase the flowrate of air through it while not disturbing the boundary layer. When the cross-sectional flow area of the duct is increased, you decrease the static pressure and make the duct into a vacuum cleaner, but without the drag effects of a plain scoop. The reason why the duct is narrow, then suddenly widens in a graceful arc is to increase the cross-sectional area slowly so that airflow does separate and cause turbulence (and drag).

NACA ducts are useful when air needs to be drawn into an area which isn’t exposed to the direct air flow the scoop has access to. Quite often you will see NACA ducts along the sides of a car. The NACA duct takes advantage of the Boundary layer, a layer of slow moving air that “clings” to the bodywork of the car, especially where the bodywork flattens, or does not accelerate or decelerate the air flow. Areas like the roof and side body panels are good examples. The longer the roof or body panels, the thicker the layer becomes (a source of drag that grows as the layer thickens too).

Anyway, the NACA duct scavenges this slower moving area by means of a specially shaped intake. The intake shape, shown below, drops in toward the inside of the bodywork, and this draws the slow moving air into the opening at the end of the NACA duct. Vortices are also generated by the “walls” of the duct shape, aiding in the scavenging. The shape and depth change of the duct are critical for proper operation.

Typical uses for NACA ducts include engine air intakes and cooling.

Spoilers

Spoilers are used primarily on sedan-type race cars. They act like barriers to air flow, in order to build up higher air pressure in front of the spoiler. This is useful, because as mentioned previously, a sedan car tends to become “Light” in the rear end as the low pressure area above the trunk lifts the rear end of the car. See the diagram below:

Front air dams are also a form of spoiler, only their purpose is to restrict the air flow from going under the car.

Wings

Probably the most popular form of aerodynamic aid is the wing. Wings perform very efficiently, generating lots of down force for a small penalty in drag. Spoiler are not nearly as efficient, but because of their practicality and simplicity, spoilers are used a lot on sedans.

The wing works by differentiating pressure on the top and bottom surface of the wing. As mentioned previously, the higher the speed of a given volume of air, the lower the pressure of that air, and vice-versa. What a wing does is make the air passing under it travel a larger distance than the air passing over it (in race car applications). Because air molecules approaching the leading edge of the wing are forced to separate, some going over the top of the wing, and some going under the bottom, they are forced to travel differing distances in order to “Meet up” again at the trailing edge of the wing. This is part of Bernoulli’s theory.

What happens is that the lower pressure area under the wing allows the higher pressure area above the wing to “push” down on the wing, and hence the car it’s mounted to. See the diagram below:

Wings, by their design require that there be no obstruction between the bottom of the wing and the road surface, for them to be most effective. So mounting a wing above a trunk lid limits the effectiveness.

Aerodynamic Design Tips

• Cover Open wheels. Open wheels create a great deal of drag and air flow turbulence, similar to the diagram of the mirror above. Full covering bodywork is probably the best solution, if legal by regulations, but if partial bodywork is permitted, placing a converging fairing behind the wheel provides maximum benefit.
• Minimize Frontal Area. It’s no coincidence that Formula 1 cars are very narrow. It is usually much easier to reduce FA (frontal area) than the Cd (Drag coefficient), and top speed and acceleration will be that much better.
• Converge Bodywork Slowly. Bodywork which quickly converges or is simply truncated, forces the air flow into turbulence, and generates a great deal of drag. As mentioned above, it also can affect aerodynamic devices and bodywork further behind on the car body.
• Use Spoilers. Spoilers are widely used on sedan type cars such as NASCAR stock cars. These aerodynamic aids produce down force by creating a “dam” at the rear lip of the trunk. This dam works in a similar fashion to the windshield, only it creates higher pressure in the area above the trunk.
• Use Wings. Wings are the inverted version of what you find on aircraft. They work very efficiently, and in less aggressive forms generate more down force than drag, so they are loved in many racing circles. Wings are not generally seen in concert with spoilers, as they both occupy similar locations, and defeat each other’s purpose.
• Use Front Air Dams. Air dams at the front of the car restrict the flow of air reaching the underside of the car. This creates a lower pressure area under the car, effectively providing down force.
• Use Aerodynamics to Assist Car Operation. Using car bodywork to direct airflow into side pods, for instance, permits more efficient (i.e.. smaller FA) side pods. Quite often, with some for-thought, you can gain an advantage over a competitor by these small dual purpose techniques. Another useful technique is to use the natural high and low pressure areas created by the bodywork to perform functions. For instance, Mercedes, back in the 1950s placed radiator outlets in the low pressure zone behind the driver. The air inlet pressure which fed the radiator became less critical, as the low pressure outlet area literally sucked air through the radiator.

  A useful high pressure area is in front of the car, and to make full use of this area, the nose of the car is often slanted downward. This allows the higher air pressure to push down on the nose of the car, increasing grip. It also has the advantage of permitting greater driver visibility.

• Keep Protrusions Away From The Bodywork. The smooth airflow achieved by proper bodywork design can be messed up quite easily if a protrusion such as a mirror is too close to it. Many people will design very aerodynamic mounts for the mirror, but will fail to place the mirror itself far enough from the bodywork.
• Rake the chassis. The chassis, as mentioned in the aerodynamics theory section above, is capable of being slightly lower to the ground in the front than in the rear. The lower “Nose” of the car reduces the volume of air able to pass under the car, and the higher “Tail” of the car creates a vacuum effect which lowers the air pressure.
• Cover Exposed Wishbones. Exposed wishbones (on open wheel cars) are usually made from circular steel tube, to save cost. However, these circular tubes generate turbulence. It would be much better to use oval tubing, or a tube fairing that creates an oval shape over top of the round tubing. See diagram below:

The Future
In the near future, Joe Sixpack will become more comfortable with the look of aerodynamic vehicles. As the model below crafted by Raymond Gage shows, aerodynamic vehicles can be quite stylish.

While this vehicle is only a concept today, economic and ecological pressures will combine in the near future to force vehicle manufacturers to build true “No Compromise” aerodynamic vehicles. Below are some more nice shapes.

Oldsmobile Aerotech concept car

Electrolite el-11, a 3 wheeled electrothon vehicle built by E. Michael Lewis

The 2007 Aptera concept, by Aptera (formerly Accelerated Composites)

2000 GM Aptera 108MPG Concept Car

1985 Ford Probe V Concept Car

High Mileage Loremo 2007 Concept Car

Honda FCX Fuel Cell 2008 Concept

The 2008 FuelVapor Alé pre-production car

VW 1 Litre concept car

2009 VW L1 concept 2

Most of the information about car aerodynamics seems to be centered around generating downforce. While this may be needed for race cars, the average 3000+ pound car driving at speeds below 90 MPH does not need to be concerned with downforce. If you are trying to improve the efficiency of your vehicle, reducing the coefficient of drag (Cd) should be the main concern.

Rationale
In this day and age of expensive fuel and inefficient vehicles, it makes sense both economically and ecologically to conserve as much fuel as possible. To accomplish this, you could go out and buy another car with better mileage, but there are other options. This article focuses on how to optimize your current vehicle.

The example vehicle is a 1998 Nissan Maxima. This is a rather boxy 4 door sedan with quite a lot of ground clearance and a 190hp 6 cyl engine, that is rated at 26MPG highway, but gets around 21MPG in mixed driving.

1998 Maxima Before mods

For highway driving conditions, it is estimated that driveline uses about 15% of the total energy to required to push your vehicle down the highway, tire rolling resistance represents about 25%, and air drag is about 60%! While the traditional sources advocate saving fuel by driving less or driving slower, there are greater gains that can be made by modifying the aerodynamics, engine, and rolling resistance of  the vehicle. These modifications are not without cost, but are within reach of even those of us with meager incomes. All of the aerodynamic modifications mentioned here can be performed for under $1000, providing you are willing to do the work yourself.

It may take a couple of years for the dollars expended in making the modifications to be paid for by the savings of gas, but a payback in that timeframe is easy to rationalize to yourself, and others.

As seen in the table above, purchasing a 4cyl econobox or a 4cyl hybrid to replace your comfy (and paid for!) 6cyl sedan would save a bunch of money every year, but not enough to pay for the replacement. If you can afford it, it does make the best sense from an environmental point of view, but purchasing an expensive new car just to save $900 per year in gas is not an option many of us can afford.  To most of us it makes more sense economically to keep driving our current gas guzzler. Modifying the sedan to get 25% better mileage, for under $1000 would start paying back after only two years. None of the modifications below in itself will provide a huge change in efficiency, but 3% here and 5% there all add up to big numbers eventually.

The 25% mileage improvement figure above is an estimate based on results I have seen of a 70 mpg Honda civic (Bryant Tucker), and a 32 MPG truck, (Phil Know).  This would be an improvement in highway mileage only. The $1000 project cost estimate would be spent on:

• Eibach height adjustable springs – ~$300.
• Aluminum sheet and hardware to build a belly pan and other aero mods – ~$300
• The remainder would be for other stuff like measuring the mileage
  

Manufacturers design most cars for looks, with aerodynamics as an afterthought. As such, much can be gained by tweaking the aerodynamics of these vehicles. The unit of measurement for aerodynamics is called the “coefficient of drag” or Cd. The Cd value tells us how efficiently the vehicle slips through the wind. Another common measurement multiplies the Cd times the total frontal area of the vehicle. This is called CdA.

Here are things that can be done to improve your vehicle’s aerodynamics:

• Lower the car – Lowering the car reduces the effective frontal area, increasing efficiency. Note that this only works up to a certain point. There will be an ideal ride height for each car. According to this, 2.7″ ground clearance is a good minimum height to shoot for. According to Mercedes, “Lowering the ride height at speed results in a 3-percent improvement in drag.”
• Remove that wing – Many “sports” cars have a non-functional wing on the back. Removing it will improve the fuel economy. The exceptions are the small rear fairings that are designed to detach the airflow from a rounded trunk.
• Clean up the underside of the car. – Installation of a “body pan”, while a labor intensive operation, will provide a significant improvement in mileage.
• If a body pan is not practical, an air dam will redirect air that would normally pile up under the car causing drag. Not as good as a body pan, but better than nothing. Should be combined with side fairings.
• Fair the wheel wells. – Yeah, this looks funny, but completely covering the rear wheel well will help improve efficiency. While the front wheel can not easily be completely faired due to clearances needed for turning, a partial fairing can be made. In addition, fairings can be added in front and behind the tires to help transition the air around these large appendages.
• Clean up the front of the car. Basically the smoother the better. If the car has a large air intake under the bumper, it may not need that opening above the bumper (they are often just styling cues). An aerodynamic plastic, composite, or foam and duct tape panel can be built to cover the opening.
• Remove the side view mirrors and instead use a remote camera system.
• Replace large whip antennas with smaller powered antennas.
• Vehicles with steep windshields can benefit from a hood fairing to help smooth the transition of air between the hood and windshield.
• A small “tail cone” can be affixed the the rear bumper to help transition the air from under the car.
• Side fairings can be used to clean up the lower half of the body between the tires.

1998 Maxima after proposed modifications. Hover mouse over body mods to see notes.

Additional mods for trucks:
If you need the utility of a truck, there are things that can be done to improve their efficiency in addition to the items noted above. Most notably, cover the bed! A flat hard cover will help some, but a custom aero cover is much more efficient. Experimentation has shown that simple removal of the truck bed door does not provide better mileage.

Additional mods for Vans and SUVs:: A new spoiler design has been shown to reduce  drag and lift significantly on bluff-backed vehicles such as minivans and SUVs. Simulations showed that aerodynamic drag on a mini-van moving at 67 mph were reduced by 5% when the new spoiler was attached. This rear spoiler acts like a diffuser when it is attached to the back of a vehicle, making the pressure on the back of the vehicle higher than without it. That’s a good thing!

Body Pans:
A body pan fairs the underside of the vehicle. This becomes increasingly important as the vehicle gets closer to the ground. The pan ideally covers the entire underside of the car, but this may be impractical in many cases, so the idea is to make it as smooth as possible. Covering the exhaust system can lead to heat buildup between the belly pan and the floorboards. In general it’s a good idea to create a heat shield/tunnel extending from the engine compartment to the rear of the vehicle. This will serve to seal in as much of the heat as possible. High pressure from the engine compartment will force air down the tunnel and out the rear of the car. Also, louvers may be cut into the body pan in areas where more heat needs to be released, such as along the route of the exhaust pipe. NACA ducts do not work well for this application as they are designed as devices to scavenge incoming air without disturbing the airflow, not as an air exhaust device. Engine airflow needs to be retained, but generally there are large enough opening between the engine compartment and the front wheels to give good engine airflow, even with the underside of the engine covered.

Toyota Prius Body Pan

Be sure to make the areas where maintenance will occur easily accessible, especially oil pan drain and oil filter access. The belly pad should be parallel to the ground until just past the rear axle, then it should gradually curve upward to meet with the underside of the rear fascia of the car. Even the most aerodynamic cars manufactured today, for example the Toyota Prius pictured here which is touted as having a full body pan, can be cleaned up extensively.

Car side fairings – “ground effects”:
Most car bodies slope inward at the sides until they are inside of the tires toward the bottom of the vehicle, leaving a large gap between the tires. Mud flaps are spiffy but only serve to make the gaps bigger. This all adds up to a lot of aerodynamic inefficiency. Side fairings “fill the gap”, transition the air around the tires and keep side winds from flowing under the car. If you are driving 60 MPH with a 20MPH side wind, 33% of the wind forces are on the side of the car, so making the side of the car aerodynamic is almost as important as improving the aero qualities of the car front. Stylists have created “ground effects” that claim to be aerodynamic, but really aren’t. Instead, a flat panel slightly wider than the tires can be installed to help fair the sides of the car. Check out the side of NASCAR vehicles for reference. This panel should extend down to meet with the body pan. The corner where the two panels meet should be rounded if possible. The hardest part of this task will be the door cutouts and clearances.  Side fairings also transition the air around those large appendages called tires.

Turbulators, etc:
In areas where the body transitions at a rate of more than 12 degrees, turbulator strips, vortex generators, diffusers, very short fairings or other devices can be used to “trip the airflow”.

The idea is that areas like the transition between the roof and rear window on the average car creates a large vortex. Any large vortices effectively grab the car and try to hold it back as it tries to slip through the air. If the air that makes up the vortex can be “tripped” before it leaves the back of the car, it will make smaller vortices, which will have a smaller effect on the overall aerodynamics of the vehicle. Measurement of the effects of these devices at highway speeds has been difficult to obtain.

Vortex generator above a Mitsubishi rear window (photo by Mitsubishi)

Tires:
Tire rolling resistance (RR) also plays a large part in the mileage of a vehicle. Running your tire pressure at higher pressures will help somewhat (do not exceed rated pressures printed on the side of the tire), but specially designed low RR tires will help more. The typical 20% reduction in RR from a low RR tire can result in fuel savings of  2% to 4%. Green Seal notes that a typical Ford focus can increase it’s mileage by 2 MPG (from 30 to 32MPG) just by replacing the stock tires with low RR tires. A caveat however, is that low RR tires do not handle as well as normal “sport” tires.

Wheel covers: Unfortunately, the coolest looking chrome spoked wheels are really bad aerodynamically. The best wheel cover is a slightly convex, completely smooth cover that fits flush with the tire. “Racing disks” like the one pictured here from JC Whitney or something similar can be snapped onto most wheels for a quick aero fix.

Temperature
Air temperature has a large effect on gas mileage. Part of this is due to rolling resistance. Because tires lose one PSI for every 10 degrees, and tires lose elasticity in colder weather, rolling resistance increases as temperature decreases. This means the tires don’t roll as well when it’s cold out. Air density also increases as temperature drops. Ralph Kenyon worked out the math to calculate how much this effects gas mileage here. His works suggests that gas mileage drops 2% for every 10 degrees F below 90 degrees due to air density alone. This means that at 40 degrees F there will be a 10% decrease in mileage.

Engine efficiency:
Modern engines are fairly efficient. Plenty of claims for products to improve your vehicles engine efficiency have been made, but few do anything worthwhile. The ones that do work are generally pricey. If you want to spend the bucks, you can:

• Install headers or a “Y pipe” to scavenge the exhaust gasses. Do not remove the catalytic converter.
• Install efficient mufflers. Note that engines do require backpressure to function properly.
• Install Under-drive pulley. Note that this will reduce engine cooling and and battery recharging. Most vehicles are designed for worst case scenarios though, so this is usually ok unless you have a 3 kilowatt stereo.
• Install a cold air intake. Most air intake systems are designed to be quiet, not efficient.
• Install a high flow air filter.
• If the radiator fan is driven off of the engine by belts, replace it with thermostatically controlled electric fans.
• Install a transmission with taller gears. Once you have made your vehicle more aero, it won’t need the power that the extra RPMs provided. Taller gears mean that the engine RPMs will be lower, which equates to less gas used.

Note that due to differences in how engines operate, changing the intake or exhaust system may not help the mileage. Generally they don’t hurt it, but you may get lower mileage due to the tendency to drive more aggressively when you can hear the engine making cool noises. Measuring is key.

Measuring your mileage:
So, you have decided to terrorize your car, and are not too concerned about what your neighbors will think. Now, how do you figure out if what you did helps or hurts your mileage? You have a couple choices.

• Record the amount of gas and your mileage and do the math. Here’s how:
  1) Fill up your car. Record the mileage.
  2) Next time you fill up, record the mileage and the amount of gas.
  3) Latest mileage minus original mileage = number of miles driven
  4) Number of miles driven divided by amount of gas = miles per gallon
  This is the cheapest thing to do, but takes a long time and is not very granular.
• Buy a mileage measurement device scanguage 2. $159 and it just plugs into the OBD port of your car. It works on almost all cars newer than 1995.
  

Fuel injection technology represents one of the main drivers towards improving current characteristics of diesel engines and identifies future enhancements to reduce engine exhaust emissions, combustion noise and fuel consumption. In parallel to the continuously growing injection pressure, the number of injection events has been increased and the tolerances of the injected quantities has been reduced, a trend that will be followed in the future.

FEV, for over 20 years, has provided piezo-electrically actuated injection systems as development tools for identification of Fuel Injection Equipment (FIE) related demands within advanced combustion development. FEV has also been one of the key developers of modern production piezo injection systems. In addition to typical diesel injection systems, FEV has continued to develop and investigate gasoline tailored injection systems, as well as dedicated injectors for exhaust aftertreatment devices or fuel cell systems.

Injection System Development

CORA RS is one significant example of FEV’s prototype injectors for combustion system

development. CORA RS uses a conventional spring loaded nozzle needle, which allows a much higher opening and closing velocity of the nozzle than current production common-rail systems. The higher velocities are possible because the rear side of the nozzle is not pressurized by the rail pressure.

The CORA RS injector also combines the common-rail system’s degree of freedom regarding injection pressure and multiple injection capability with the flexible forming of the injection rate and minimized nozzle seat throttling.

Production System Investigation

Standard production engine development projects are supported by dedicated fuel injection system investigations, in addition to the innovative research work that is performed on unique prototype injection systems.

Using computerized injection test benches, the performance of the injection system is automatically measured and documented through the following methods:

• Injected quantity vs. Energizing duration
• Standard deviation of injected quantities
• Influence of the intervals between pilot, main and post injection
• Injector stability (aging and coking)
• Full system durability investigations

Special Sensors for Fuel Injection System Analysis

The size, dynamic and environmental boundary conditions of fuel injection systems often require the application of specially developed sensors, because these sensors are not commercially available. The retroaction of these sensors on the injection performance has to be reduced as far as possible. Some examples of special sensors that have been developed:

• Nozzle needle and/or valve lift sensors
• Pressure measurement in a servo control chamber or at the nozzle side
• Dynamic pump drive torque and/or power consumption
• Temperature measurement
• Actuator force measurement

The Ford Fusion 1.4 Durashift Offers A Method Of Changing Gear That Keeps You In Control But Makes City Driving A Piece Of Cake.

When it comes to cars for the urban jungle, there can be few better candidates than the Ford Fusion Durashift. Here is a vehicle thats in its element in the sort of traffic that would reduce a Gregorian monk to wheel-thumping, vein popping frustration. If you really want to make the urban sprawl and crawl your own, heres the car for the job.

Combine the elevated ride height of the Fusion body with the clutchless Durashift EST gearbox and youre onto a metropolitan winner. Ask many drivers committed to manual gearboxes what they dislike most about a conventional automatic and it would probably be just that: the removal of that vital element of control. Weve all driven poor automatics that change up halfway through corners, thus depriving us of grip. Either that or theyll snick the next gear up as you start descending a hill, ensuring that you wear through brake pads at double the normal rate. Durashift EST is different.

Its a clutchless manual gearbox that retains all the control, performance, low cost and economy of a manual box, along with the convenience and simplicity of an automatic. Thats Fords party line at least. If you just want the simplicity of a conventional automatic, you can have one but only with the 1.6-litre engine.

DESCRIPTION:

Three tiny electric motors take the place of the clutch pedal and the cables normally required by the clutch and shifting mechanisms. Two of these motors do the shifting work on the drivers behalf and the third motor, supported by a hefty spring, actuates the clutch. So yes, despite there being no clutch pedal, you still get a clutch. To engage the manual SSM mode, the driver merely has to move the lever from the D position and tip the lever back to change up and forward to change down.

Unlike most systems which can be a little jerky, the Fusion Durashift is easy to flick smoothly up and down the gearbox, the engine even blipping instantaneously on downshifts to match the revs for you. The key difference between Durashift EST and many other sequential manual transmissions is the quality of the software in full automatic ASM mode. Drop the lever into D and roll away and youll probably appreciate the syrupy smoothness, but theres a whole lot of clever programming behind it. The Transmission Control Unit (TCU) is a box of tricks that gathers information from a number of sensors, analyses driving styles and communicates with the cars main brain, the engine control unit (ECU).

This allows the Durashift-equipped Fusion to include a number of clever driving strategies. It has a downhill detection system that compares vehicle acceleration and driving torque. When the downhill mode is activated, the system reacts by forbidding upshifts below a certain engine speed. When the brakes are applied, the system downshifts to a lower gear ratio.

Likewise, the system has strategies for driving uphill or when driving against resistance, for example when pulling a trailer. Theres a curve detection mode to prevent unwanted gearchanges midcorner and a fast-off detection system that stops the gearbox upshifting if the drivers foot flies rapidly off the accelerator a typical response when he or she is unsure of the road ahead or about to hit the brakes. Like any automatic, theres even a creep function that eases the car forward when in D or backwards when in R, prolonging the life of the clutch in stop/start traffic and making the whole process a good deal smoother. As you would expect from anything based on a Fiesta, the handling is very good.

Although the tall Fusion looks like something that may be slightly top heavy, your first corner will rapidly dispel this impression. Somehow Ford seem to have engineered a ride thats able to absorb the ruts and bumps of city streets with a chassis that enjoys spirited driving. Refinement is a mixed bag, the 1.4-litre engine being reasonably well behaved at higher speeds with tyre and wind noise making a significant intrusion.

The 1.4-litre engine needs to be worked quite hard to make respectable progress, hitting 60mph in 13.5 seconds on the way to 101mph. CO2 emissions are reasonable, the Fusion pumping out 154g for every kilometer traveled.

Likewise, you will not be taken to the cleaners at the pumps, the 43.5mpg average fuel consumption a fine effort. Even around town you can expect to see over 33mpg. Many industry experts were a little puzzled when the Fusion was first introduced, wondering whether the public would take to this elevated Fiesta.

Refrigerant is pumped around the air conditioning system, which is split into 2 parts: the high pressure side (top, red) and the low pressure side (bottom, blue). The refrigerant vapour is drawn from the low pressure side to the high pressure side by the compressor (A). In this process the vapour is heated to a temperature of between 25-75 degrees centigrade.

The hot vapour is then pumped to the condenser (B) which consists of a series of pipes surrounded by a cooling core. The refrigerant vapour is cooled by the air stream, with the assistance of the condenser fan (or radiator fan) so that it condenses into a liquid.

The liquid refrigerant then flows into the receiver drier which stores and filters the refrigerant until required by the evaporator (C).

The suction effect of the compressor (A) on the low pressure side of the circuit “sucks” the liquid refrigerant through the “controlled restriction”. This causes an abrupt drop in refrigerant pressure as it passes through the “controlled restriction”, which causes the liquid to evaporate. During the evaporation process heat is extracted from the air passing across the evaporator coil (C). This cooled air is then blown into the vehicle.

When buying a new, recalls and defects are always a concern. What is a defect? Why did they do a recall? Where can I report a possible defect or need for a recall? These are all very important questions and can sometimes be tough to find answers to. In the section on Motor Vehicle Defects and Recall Campaigns all your questions, and even a few you didn’t know you had, are answered. Understanding a recall or a defect on your car can save you a great deal of money. In the event of a recall on part of your car, the dealership where you bought it will fix the recalled part for free. If you didn’t know this, you might be out the money that you paid to get the part fixed elsewhere. This section is very informative and helpful. You might even want to take a look at it before you buy a car so you will know what questions to ask the dealership about and recalls or defects they may have had.

Nothing beats the smell of a new car, the thrill of driving away in a car that is yours, one that’s never been owned by anyone else, but it comes at a price in the form of depreciation. You can virtually write off 20 per cent of the purchase price the moment you drive away from the dealer because it’s then a used car. Cars depreciate faster in the first two or three years of their life and the new car buyer has to cop that for the pleasure of being the first owner. By buying used it’s possible to avoid the heaviest depreciation. Cars will still depreciate in their latter years, but at a lower rate.

• New car buyers can choose the colour of their car, the trim colour, the engine, transmission and other options and accessories, but used car buyers have to take what’s available.
• New car buyers have the reassuring backup of a new car warranty so they know that if anything goes wrong they won’t be up for a big repair bill. Anyone buying from a used care dealer will also have a warranty, but it won’t be for as long as the new car warranty. Private buyers don’t have any warranty.

Negotiating with Dealers

It’s a buyers market which means you can bargain with dealers for a better deal, but you need to be prepared for the battle.

• Do some homework on market values before you go shopping so you know the value of the car you’re buying and the value of your trade-in. That way you’ll be better placed to barter with the dealer.
• Have your finance arranged before you go shopping, but don’t tell the dealer. Dealers will often cut the price of a car believing they’ll make money on the finance.
• Don’t settle on the first car you inspect. Visit a number of dealers and compare deals before making a commitment.
• Look for a dealer well stocked with the car you want and he’ll be more prepared to deal.
• Shop towards the end of the month when dealers are looking to get their quotas up.

Financing your wheels

Few of us are able to hand over a wad of cash to pay for our car, we all need finance for the purchase.

• Before you start work out how much you afford to pay, and how much you can afford to repay.
• Don’t be tempted to use your credit card to pay for your car, the interest rate on credit cards is generally very high.
• Shop around to save money.
• Finance through dealers is the most expensive, dealers are on-selling the finance to you and they are making a profit on the deal, so cut out the middle man and go straight to the source of the finance.
• Banks offer finance at a cheaper rate than the dealers, but approval can take time.
• Independent finance companies specializing in car finance often have the lowest interest rates, and some offer fast approvals with an on-line service.

Where to Buy

• Buying from a dealer gives you the security of a warranty. By law dealers have to give you a warranty which gives you some recourse if something goes wrong with the car later.
• Dealers also have to guarantee ownership of the vehicle, that there is no outstanding finance on it which might complicate matters later. They also have to guarantee the odometer reading.
• It’s possible to buy cars cheaper at auction, but there are risks. There’s little chance to check a car over, there’s no chance to drive it, so you take a risk on its condition. The auction environment is not one for the faint hearted, it’s fast moving with lots of little nods, winks and gestures for those in the know. Spend the time to visit auctions to become familiar with them before attempting to join in the action. It’s a good idea to take along someone with mechanical knowledge to help you assess the cars before the auction starts.
• Buying privately can be a way of saving money, but it can be risky for the unwary. There is no comeback with a private purchase, once you’ve driven away you’re on your own.

Before you buy a car ask yourself:

• What kind of driving do you do?
• Off road? Around town?
• What features matter to you?
• Air-con? Safety? Power?
• What’s your price range?
• Where will you be parking?
• Do you have a garage or only on-street parking?
• What kind of insurance can you afford?