the t25 is the standard turbo on your ca18det.
T25 is pritty punchy, comes on boost about 2,200rpm... can run a max of 14psi as adaily driven turbo but as they are a ceramic compressor wheel they dont like 2 be boosted up more than that as they wear real quick.
T28 much better turbo a good upgrade from t25 can source one of these of s15 200sx
these turbo's when got about 15psi run through them come on boost alittle latter on rev range but really pull alot harder than t25
t28 can be boosted up about 20psi mark..
both these turbo's can be high flowed but u better of saving your money and buying a GT series turbo as ther are rollerbearing much better quality.. hope thats helped u alittle more!