Originally posted by lostyouth
ok, been searching and searching and cant find anything but domestic sites with explanations of the difference between turbochargers and superchargers 
Would really like some questions explained or at least pointed in the right direction (link)
what exactly is A/R, what am I lookin for;
pros and cons to bigger and smaller a/r housings
A/R is Area/Radius. (as in divided by) These specs are on both the compressor and turbine housings, however, it is more important on the turbine housing and the compressor a/r spec is usually disregarded. Usually the bigger the #, the more flow it will cause the compressor to have, but at a cost of more lag. The smaller the number, the less lag, but go too small and it will cause the compressor to max out at some point and it will choke and not make power past that point. Common exhaust a/r's for say a T3/T4 turbo are .48, .63, and .82. .63 is a good one to use, but a .48 might work well on a 4 cylinder with less than 2 litres, wanting quick spoolup and not shooting for alot of power. .82 might be better for wanting a top end setup, at the cost of more lag obviously, but it will allow an engine to flow all it wants.
maybe an explanation of inducers
inducer is just a term for the compressor wheel. there is also a major and minor inducer diameter. the major one is the bigger one nearest the center of the turbo, aka against the housing if you can get what im saying. the minor diameter will be the smaller one, nearest the "tip" of the wheel, nearest where the bolt that holds the wheel onto the shaft is.
same applies for the exducer, aka the turbine wheel.
flow - lbs/min / cfm, Im guessing this tells you the turbos max boost??? maybe a way to guesstimate lbs min converted to boost
lbs/min and cfm are just two different ways of telling the same thing, such as using english or metric system.
a good rule of thumb for alot of turboes is that lbs/min is usually an approximation of the max horsepower achievable with that turbo. (i.e. - Nissan T28 from Pulsar GTi-R is rated at ~310lbs/min, and most people using that turbo max it out around 300-320hp.)
and finally wheel stages
is this a standard form to all turbos?
what are the differences between a stage 3 and stage 5?
i am not very educated on stages and what it is exactly, but i want to say it has to do with the degree/angle of the exhaust blades and the orientation/number of blades as well. i cant really answer this to the best of my ability, but i do know that a stage 5 will flow more than a stage 3.
Corky Bell's "Maximum Boost" is a good source for learning about these specifications, check
www.howstuffworks.com as well. i believe it has some basic definitions on them and some diagrams to show you how to measure a/r if you so desire.
ps - many times, the turbo housings will have the a/r's stamped into them. the trims might be too, but usually arent since if they are interchanged, it would be false information on the housings.