The ideal gas law states that when all other variables are held constant, if pressure is increased in a system so will temperature. Here exists one of the negative consequences of turbocharging, the increase in the temperature of air entering the engine due to compression.Turbocharger
A turbo spins very fast; most peak between 80,000 and 200,000 RPM Turbocharger(using low inertia turbos, 150,000-250,000 RPM) depending on size, weight of the rotating parts,Turbocharger boost pressure developed and compressor design. Such high rotation speeds would cause problems for standard ball bearings leading to failure so most turbo-chargers use fluid bearings. These feature a flowing layer of oil that suspends and cools the moving parts. The oil is usually taken from the engine-oil circuit. Some turbochargers use incredibly precise ball bearings that offer less friction than a fluid bearing but these are also suspended in fluid-dampened cavities. Lower friction means the turbo shaft can be made of lighter materials,Turbocharger reducing so-called turbo lag or boost lag. Some car makers use water cooled turbochargers for added bearing life. This can also account for why many tuners upgrade their standard journal bearing turbos (such as a T25)Turbocharger which use a 270 degree thrust bearing and a brass journal bearing which only has 3 oil passages,Turbocharger to a 360 degree bearing which has a beefier thrust bearing and washer having 6 oil passages to enable better flow, response and cooling efficiency. Turbochargers with foil bearings are in development which eliminates the need for bearing cooling or oil delivery systems, thereby eliminating the most common cause of failure,Turbocharger while also significantly reducing turbo lag.Turbine shaft