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Tech of the Turbo 1.0 – What the hell are all these numbers ??

Posted on 01 January 2011 by admin

This guide is to provide information on turbochargers, what’s inside a turbocharger and how it works, what is included in a turbocharger kit, and then right into the technical side of things so you can understand what type or size of turbo will suit what engine/set up, what terminology like 60 trim turbine mean and why everyone you know seems to pretend to have a friend with some T66 bullshit car that runs a over-rated amount of boost that usually turns out to just be a misfiring ford laser, So lets start with turbocharger terminology so that you will understand what I am talking about later on down the track.


Class 201 – Terminology

  • CHRA, Centre or Cartridge – This is the centre of the turbocharger that hold the bearings, the seals and shaft, oil flows in for lubrication, common and factory turbochargers also have coolant passages surrounding it to keep it cool known as a water and oil cooled turbo, some Turbo Diesels and aftermarket turbocharger kits are oil cooled only, essentially the CHRA is a turbocharger without the compressor and turbine housing.                                            *CHRA = Centre Housing & Rotating Assembly
  • Wastegate – This device is designed to limit boost a turbocharger is allowed to create. This is done for two reasons, one to protect the engine from over-boosting, two to prevent you blowing your turbocharger as they are only designed to spin up to a certain rpm. It works by a Pneumatic Actuator (air valve) that connects to a valve which can be mounted into the turbine housing itself (Internal Wastegate), Or can even be mounted in the exhaust manifold before the turbo (External Wastegate), A Line from the compressor housing to the pneumatic actuator allows it to sense to boost pressure and open the Wastegate, the turbo is able to limit its maximum boost output. This result is increased durability, quicker time to boost, and controlling of the boost levels depending on the setup.
  • Free-Float – A free-floating turbocharger does not have a wastegate, this turbocharger is not able to control the amount of boost. These are seen on large applications mostly dieses, but for performance an external wastegate is a must.
  • Trim – Basically it is a area ratio used to summarise the turbine and compressor wheels in one neat little formula, the trim is calculated by using the diameters of the inducer and exducer  to give you one unit like 62 Trim, the greater the trim is the more air flow the wheel is capable of, Example how to find the trim below:
    Compressor wheel Inducer diameter = 61.4mm
    Compressor wheel Exducer diameter = 82mm
    Trim = Compressor Inducer2/ Compressor Exducer2
    Trim = 61.42/822 = 56 Trim

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