A turbocharger has two main sections – hot and cold. These two sections are covered by two housings, turbine housing and compressor housing. In the other discussion we’ve posted on Arashi Blog section, it discusses about how to choose the right sized turbine housing; in this article, we’ll discuss about the compressor A/R, which is also the size of the compressor housing.
A/R is short for area/radius, its definition is the discharge, cross-sectional area divided by the radius from the turbo centerline to the centroid of that area. Don’t be annoyed by the calculation, usually A/R is specified when you purchase a turbocharger. The larger the number, the bigger the housing is, on the contrary, the smaller the number, the smaller the housing is.
Compressor A/R plays an insignificant role compared to turbine housing; therefore no one actually discuss about it in depth. Bigger A/R housings are used sometimes to maximize low boost applications, and smaller A/R are used sometimes for high boost applications; with very little effects though.However, Arashi often gets the question of, I have purchased certain A/R turbo but it has another number A/R on my housing, am I getting the wrong turbo? Please note that as turbine housing A/R is one of the most important factors in choosing a turbo, Arashi specifies turbine housing A/R on our product lists only, but the A/R number on the front of compressor cover is much more noticeable when seeing the actual turbocharger, hence many people misunderstood it as the turbine A/R.