TURBOCHARGERS VS SUPERCHARGERS

Perfect Power Articles.

 

Talk to two people, and you will get three answers. Here are some considerations in deciding which one is the right choice for you:

 

  • Turbochargers fit easily on straight 4 or 6 cylinder engines. They must be fitted as close as possible to the head.
  • Turbochargers run very hot, just short of melting down. Therefore, the Turbocharger surrounding must be well insulated from radiating heat. It is advisable, that the engine must be kept idling for a minute or two after heavy use before switching off. Turbochargers are water-cooled.
  • Turbochargers run hot because they rely on the exhaust gas velocity, which is directly proportional to the temperature.
  • Turbochargers have turbo lag, i.e. the time it takes to wind the "fan" up. This is less noticeable with automatics or during manual gear shift, but very noticeable during a "standing start".
  • Turbochargers are more commonly used in diesel engines.
  • Turbochargers are used more frequently in Europe because smaller engines (4 cylinders) are more common.
  • Turbochargers require a special exhaust branch, which must be made of high temperature material. And if possible with no heat expansion! Otherwise your exhaust branch gasket will not last.
  • You can fit two Turbochargers on a V6 or V8, it will work, but you must choose the type of Turbochargers carefully. You also need to consider that you'll have twice the radiation heat problem and twice the cost.
  • Superchargers are used exclusively in acceleration racing, because the turbo's lag can't be tolerated.

 

Another way to explain a Turbo's lag, is that a Turbocharger works on the chain reaction principle. It is the starting of the chain which produces the lag. Let's assume the engine idles and so does the turbo. The boost pressure is ZERO. Then you open the throttle to a particular point and keep it there. The engine operates in a decompressed state and produces very little power. The little power it makes raises the exhaust gas temperature and velocity. This makes the turbo spin a little faster and raises the boost pressure, which in turn makes a little more power, which in turn.....(the chain reaction sets in). The chain reaction is limited by the waste gate regulation, and the airflow through the butterflies. Also, the Turbocharger can limit the boost pressure, or RPM limits can come in to play, or your engine could blow up.

Depending on the type of Supercharger you are considering, the fitting varies from being almost impossible to as easy as fitting an air-conditioner pump.

 

  • Turbochargers are used on constant load engines such as trucks, marine engines and power-plants.
  • There are many types of Superchargers, but only one type of Turbocharger. The selection of the correct size and manufacturer of either Turbocharger or Supercharger is an art, which should be left to the experts. Many technical books have been written about it and free advice is available from the manufacturers of Turbochargers or Superchargers.
  • When you look at the boost pressure curve of Turbochargers and Superchargers, the Superchargers don't look too impressive. This is because they have to be geared to produce the maximum boost pressure at high RPM. In comparison, a Turbocharger has a regulation device built in, which opens a "waste gate" once the maximum boost has been reached.
  • The Turbocharger's curve doesn't explain or show the Turbo's lag!
  • A Turbocharger produces more power at low RPM. This is because a well-selected Turbocharger produces the maximum boost between 2000 to 2500 RPM, when the waste gate starts to open. In the latest Turbocharger designs, the turbo fan has become smaller, the waste gate bigger, and the turbo speed higher.
  • Turbochargers can't really produce very high boost pressure, above 1.5bar (21psi). Someone will prove me wrong, I am sure, but Turbochargers are used normally between 0.4 to 1.2 bar (6psi to 17psi).
  • Superchargers are more predictable in engineering terms. From the manufacturer's data you can choose the correct gearing for the desired boost pressure and RPM.
  • Superchargers are more expensive and difficult to manufacture.
  • Superchargers heat the boost air to the same extent as a Turbocharger.

 

Summary: If you have a straight engine, not used in a dragster, consider installing a Turbocharger. Turbochargers are less expensive, but require a some engineering. Alternatively, you can consider a Supercharger. Do some market research as to the type, size, lubrication, cooling and gearing required. If you are building a dragster, you should install a Supercharger. Most Supercharger manufacturers offer kits and provide very helpful advice.