Blog — turbo tech

Courtesy of TurbobyGarrett.com ( http://turbobygarrett.com/turbobygarrett/compression_ratio_with_boost ) Before discussing compression ratio and boost, it is important to understand engine knock, also known as detonation. Knock is a dangerous condition caused by uncontrolled combustion of the air/fuel mixture. This abnormal combustion causes rapid spikes in cylinder pressure which can result in engine damage. Three primary factors that influence engine knock are: Knock resistance characteristics (knock limit) of the engine: Since every engine is vastly different when it comes to knock resistance, there is no single answer to "how much." Design features such as combustion chamber geometry, spark plug location, bore size and...

Courtesy of www.TurbobyGarrett.com A/R (Area/Radius) describes a geometric characteristic of all compressor and turbine housings. Technically, it is defined as: the inlet (or, for compressor housings, the discharge) cross-sectional area divided by the radius from the turbo centerline to the centroid of that area (see Figure 2.). Figure 2. Illustration of compressor housing showing A/R characteristic   The A/R parameter has different effects on the compressor and turbine performance, as outlined below. Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R...

Courtesy of www.TurbobyGarrett.com On the exhaust side, a Wastegate provides us a means to control the boost pressure of the engine. Some commercial diesel applications do not use Wastegates at all. This type of system is called a free-floating turbocharger. However, the vast majority of gasoline performance applications require a Wastegate. There are two (2) configurations of Wastegates, internal or external. Both internal and external Wastegates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level....