Was not my intention to stir the $hit, I explained why I was confused and even with all the typical young guy jokes, I still am not totally sure I understand how it works. I have searched to try to find the conversion for cm2 and also to better understand the A/R given. Everything I find says the A/R is dependant on the housing used and other factors, I appreciate the link Howling sent me, but that just explains the smaller housing is better for low end and spools faster, which I understand that part. The part I don't understand is, according to the search function, a .83 A/R on T3 is a different size than a .83 on a T4 housing, so just because they are the same number doesnt mean they are the same size. Maybe I should've just asked if this turbo would work spool well with my 97 12V cummins running 5x14s, just dont want a laggy turd, plan on using the truck as a daily/ light tow and didnt want something with a huge exhaust housing that doesnt light until 2200rpm. Sorry to those I offended, perhaps I took his comment to be more of an a$$hole comment than it was intended to be. Apologize for the hijack, but I am serious about the turbo.