Blog — turbobygarrett

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...

More Great Turbo Tech from www.TurbobyGarrett.com There are two different types of turbocharger manifolds; cast log style (see Figure 3.) and welded tubular style (see Figure 4.).    Manifold design on turbocharged applications is deceptively complex as there many factors to take into account and trade off . General design tips for best overall performance are to: Maximize the radius of the bends that make up the exhaust primaries to maintain pulse energy Make the exhaust primaries equal length to balance exhaust reversion across all cylinders Avoid rapid area changes to maintain pulse energy to the turbine At the collector,...

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 Getting a little more complex here. Trim is a common term used when talking about or describing turbochargers. For example, you may hear someone say "I have a GT2871R 56 Trim turbocharger". What is 'Trim?' Trim is a term to express the relationship between the inducer* and exducer* of both turbine and compressor wheels. More accurately, it is an area ratio. * The inducer diameter is defined as the diameter where the air enters the wheel, whereas the exducer diameter is defined as the diameter where the air exits the wheel. Based on aerodynamics and air entry...

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....