T4 and T88 both denote two turbos of different sizes. A straight T4 would be pretty laggy on a street driven Honda, which is why there are hybrids like T3/T4, T3/T04b/e, etc. The smaller T3 turbine is mated to a T4, T04b, T04e compressor housing to combine the quicker spools of a T3 turbine, and higher CFM of a T4 compressor. A T88 is a pretty large turbo which you probably won't find on an Hondas, except maybe a pro-drag car. They're usually used to upgrade the smaller twin-turbo setup on an MKIV Supra to a larger single-turbo setup.