what are ball bearing turbo's? some have dual ball bearing and some has single. what's the difference? what are they good for? what do they do? how can you tell if it's a ball bearing?
Ball bearings live longer lives than their cheaper, main counterparts which are sleeve bearings.
Ball bearing turbos also have less rotational resistance than their
sleeve-bearing counterparts. Which, in turn, allows the turbo to spool up
faster and have a better transient response than a sleeve-bearing turbo.
About the longevity of the ball bearing turbo. In perfect operating conditions, you're completely correct. But, a ball bearing turbo is much, much more sensitive to little debris in the oil being run through the CHRA. Many people will run an additional oil filter in the turbo oil-feed line. Also (not a down side), you must run low pressure oil to a ball bearing turbo, whereas a sleeve-bearing turbo requires high pressure oil (like the crankshaft, rods, camshaft, etc). So, if you're upgrading an existing turbo setup from a sleeve-bearing turbo to a ball-bearing turbo, you need to be aware of that difference.