I've compiled a list of definitions related to turbos, they are organized here alphabetically:
A/R – a formula used to determine the size of the compressor and housing configuration. It stands for Area divided by Radius, where the area is the cross-sectional area of the scroll(turbine wheel) and the radius is the shortest distance from the centerline of A to the centerline of the shaft. A turbo with a smaller A/R will spool faster but produce less power than a turbo with a larger A/R which will spool slower but produce a higher peak power.
Bar – Bar is just another pressure measurement like PSI, 1 bar = 14.5 psi, it is commonly used because it is approximately equal to standard atmospheric pressure
Bearing – Bearings are found all over the car, they are a mechanism which supports the load and reduces friction, especially where spinning is occuring. As far as turbos are concerned, the shaft that connects the turbine and compressor wheels through the center housing ride on a bearing that allows it to spin. There are two types of bearings, standard metal bearings and ball bearings. The standard metal bearings are a layer of metal which a thin layer of oil on it, which allows it to spin freely, they wear over time but can be rebuilt if damaged. Ball bearings use small metal balls that reduce friction and allow the turbo to spool sooner, speeding up the turbo’s response time. Ball bearings, however, are much more expensive to re-build if damaged.
Compressor – The intake side of the turbo which is connected by a shaft to the turbine. It is another finned wheel that sucks fresh air from the intake pipe through the center inlet and pushes (compresses) it into the piping leading to the engine.
Down pipe – exhaust pipe that connects the post turbine exhaust side of the turbo to the rest of the exhaust system. A larger down pipe allows freer flowing exhaust and less backpressure which allows for the turbo to spool faster as exhaust gasses move through faster.
Housing – snail shaped enclosure of the turbo, houses both the compressor and turbine. The size and shape of the housing affect the turbo’s output and heat dissipation. The larger the housing, the more boost it can produce, however, it also spools slower and makes full boost higher in the powerband.
Trim – measure of the size of the compressor and/or turbine wheels.
Turbine – finned wheel on the exhaust side of the turbocharger. The turbine is driven by the flow of exhaust gas coming out of the engine and is connected to the compressor side of the turbo by a shaft, which in turn spins the compressor wheel.
Turbo timer – a turbo timer is a small timing device that keeps the car running for a time (usually user defined) after you get out of the car. Turbos get very hot and are cooled by motor oil which is circulated through it to keep the bearings lubricated, if the turbo is very hot, and you shut the engine off, the oil flow stops and the oil that is in the turbo can burn and leave a residue on the moving parts, a process called “coking.” The turbo timer lets you get out of the car but it keeps the engine running at idle so the turbo is not producing any more heat but the oil is still circulated through it as it cools so that the oil is not burned on. This accomplishes the same thing as sitting in your car for five minutes after driving to let it cool down, it is merely a convenience that allows you to leave the car while this process happens.
