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Article from: Sport Compact Car Magazine October 1994

The term "turbo" or "turbocharger" is frequently heard in the world of high-performance. However, many people are unfamiliar with these devices and this is unfortunate, because turbocharging is one of the most cost-effective methods of producing maximum horsepower per dollar.

The turbo itself is a relatively simple device. Its moving parts basically consist of two wheels mounted on a common shaft; the turbine wheel and compressor wheel. The shaft is mounted in oil-fed bearings inside a compact center housing and the wheels are located at either end of the shaft, each one in its own housing. In function, exhaust gases leaving the engine are directed into the turbine housing. This housing directs. the high-velocity gases at the turbine wheel, causing the wheel to rotate. After the gases have passed through the turbine wheel, they exit the turbine housing and are discharged through the vehicle's exhaust system. The rotation of the turbine wheel drives the compressor wheel (which is at the opposite end of the shaft). As the compressor wheel spins, it inducts air into the compressor housing. There it is compressed and discharged into the intake system of the engine, providing boost pressure. A turbocharger creates horsepower by forcing more air into an engine than that engine could normally ingest during the intake portion of its cycle. It does this by compressing air then forcing it into the intake manifold and ports. This additional pressure is known as boost pressure. Boost pressure is typically expressed in pounds per square inch or millimeters of Mercury. This gives us an indication of how much additional airflow and pressure there is
available to the engine when the turbo is operating. The amount of boost pressure is usually determined by a wastegate. This device is frequently an integral part of the turbine housing. It functions by passing exhaust gases around the turbine wheel so that the amount of exhaust driving the turbine is limited. In this way, by opening the wastegate at a preset boost level, we can control the speed of the turbine wheel (which is driving the compressor) to maintain that boost pressure without overboosting or providing the engine with too much airflow and pressure.

Supercharger VS.
Many people are confused about the differences between a super charger and turbocharger. Booth families of devices are basically air compressors, but they're operated' quite differently from each other. A supercharger is mechanically driven by the engine itself; usually off the crankshaft by a cogged belt and pulley system. This means that a supercharger uses up some of the engine's horsepower just to drive itself - often 60 horsepower or more! Fortunately, the airflow generated by the supercharger helps it produce far more horsepower than it requires to operate.

A turbocharger, however, is driven by the thermal energy of the exhaust gases of the engine. With non-turbocharged vehicles, these gases are simply discharged out of the engine as quickly and efficiently as possible, wasting a surprising amount of energy in the form of noise and heat. A turbocharger uses some of that energy (which would otherwise be wasted) to drive its
compressor, without the attendant horsepower loss of a crankdriven system.

The result? The turbocharged engine stands to produce more peak horsepower than a comparable supercharged engine, mostly because the turbo does not require any power from the crankshaft. Also, the turbocharged engine will typically run much quieter than a supercharged engine since the turbo has no gears, belts or pulleys and because the turbo itself muffles the exhaust. And while many superchargers are large, heavy devices (we've all seen Roots-type blowers sticking up through the hoods of muscle cars), the turbocharger is a relatively small package - a turbo capable of producing 600 horsepower can weigh only 15 pounds and be easily held in one hand. It is for these reasons that turbocharging has become increasingly popular with both OE and aftermarket manufacturers. Automakers can produce lightweight vehicles with good fuel economy yet excellent power thanks to the turbo. The aftermarket manufacturers have jumped into the game, offering larger turbocharger "upgrades" in place of factory turbos, or even complete turbo "kits" to convert a naturally-aspirated vehicle to turbocharged configuration. One question we hear quite often at SCC is whether a normally-aspirated engine can be turbocharged. Any engine can be turbocharged, and there are a number of turbo kits available to allow you to do this to a variety of vehicles. However, if you cannot locate a kit for your vehicle (or you choose not to purchase an existing kit), you can build a custom installation yourself.

The fundamentals are basically these:

* Exhaust must be routed to the turbine inlet of the turbocharger. This is typically done with a turbo exhaust manifold, when available, or a custom adapter plate to allow you to mount the turbo to the factory exhaust manifold.

*Exhaust must be directed out of the turbine discharge of the turbocharger. This can typically
be done at a muffler shop, where a custom down-pipe will be fabricated, to connect the turbine
discharge side of the turbo to the exhaust system.

*Air must be ducted from the air filter to the compressor inlet, and from the compressor
discharge to the intake manifold. This is typically done in aluminum or steel tubing which is then coupled at all joints by silicone hose couplings or nitrile rubber connectors. Flex hose is sometimes used on the inlet side of the compressor since it is only subjected to vacuum, not pressure.

*Pressurized oil must be fed to the turbocharger's bearings. The most common place to tap into an oil galley is at the oil pressure sending unit.

*An oil drain line must be installed so that the oil used to lubricate the turbocharger can drain back to the oil pan. This is typically done by brazing a hose fitting to the pan and using a large diameter, oil-resistant hose from the bottom of the turbo to the side of the pan. The heart of the turbo system is of course, the turbocharger itself. The size and model of turbo that you require can vary radically depending on your application (i.e. street, track, drag). The larger turbochargers can produce tremendous amounts of power, but they will take longer to spool up (turbo lag). This is a function of the size of compressor and turbine wheels, as well as the turbine housing itself. A turbocharger applications specialist will be able to assist you in
choosing the proper turbocharger for your car.

Boost Control Devices
There are a variety of kinds of boost controls on the market. Some control air flow in and out of the compressor (such as pop-off valves or restrictors), but the most efficient (and for this reason the most popular) are controllers that work on the turbine side, which are known as wastegates.

As mentioned earlier in the article, the turbine wheel is driven by exhaust gases. A wastegate functions by taking a portion of the exhaust gas that would drive the turbine wheel and rerouting to bypass the turbine wheel. This way we can control the speed of the turbocharger and therefore, limit the boost the turbo produces. A boost control should be used so that you can limit the total amount of boost to the engine to prevent detonation.

There are other details to contend with, such as fuel enrichments, ignition controls, where and why to install check valves in vacuum lines, and so on. Therefore, it will be very helpful to both you and those helping you if you do your homework ahead of time. There are several useful books written specifically on the subject of turbocharging, some of which are available from bookstores.

Is turbocharging safe for
my engine?

There are several factors to take into account when turbocharging a vehicle. First, if the engine has high mileage and/or a good deal of wear, your money may be better spent freshening up the rings, bearings, valve guides, etc. before you invest in a turbo system. The additional stress put on the engine's internal components by the increase in horsepower may cause a weak engine to expire!

Furthermore, you -should determine whether, the engine's compression ratio permits the addition of a turbo. Since we're already compressing the charge air with the turbo, the higher the engine's static compression ratio is, the greater the tendency toward detonation. In other words, the higher your compression, the less boost you can run.

You must also take the fuel and ignition systems into account. I your fuel injection or carburetor going to be able to compensate for the additional airflow generated I the turbocharger and add a corre sponding amount of fuel under boost? Is your ignition system cap able of retarding the spark timing under boost, if necessary? Both fuel and ignition systems must be up the engine's demands, as the incorrect fuel delivery or spark timing can cause harmful detonation( Of course, correct fuel delivery and spark timing can make a great deal of

In our opinion, when properly installed a turbocharger system is capable of producing the best bang for the buck. When factoring in its reasonable cost, relatively compact size and adaptability to any sport compact car, turbocharging makes a whole lot of sense for the
enthusiast seeking big time horsepower gains!

For those that can't get enough of turbo-related goodies, check out the Turbo Club Of America. A one-year membership entitles you to club discounts on performance equipment from participating manufacturers and six issues of Turbo Club News plus much more!

Author Chris Weisberg is a Turbocharger Specialist for Turbonetics, Inc., manufacturers of custom turbochargers and controls.

I drive a slow car.
0 to 60 in 11 seconds (look out!)
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