Turbine housing Ratios. What are they?

[mramc3]

so what do the a/r numbers mean when rating a turbo? also, will an AGP T3/T4 Turbo - 50 trim, .63 AR housing hit 400whp with the proper tunning and supporting mods?

 

[KFT0001]

The A/R number is the ratio of two measurements in the turbine section. I'm not too well versed in all the lingo so I don't know what they're called exactly. Anyway, this dictates turbine speed and is directly related to how much torque is applied to the compressor. A lower number is a quicker spooling/ lower power turbo while a higher number is the opposite. A .63 A/R is on the low end, so that would make it a responsive turbo.