The format for most Volvo engine designations is: Bxxy

Where "xx"=size of engine in liters (e.g., B18= 1.8 liters, B20=2.0 liters, B21=2.1 liters, B23=2.3 liters, and so on).

Where "y"=Fuel system. 'F' is low-compression fuel injection, 'E' high-compression fuel injection. 'A' single carbs. 'B', I think, is dual carbs.

"T", as you intuit, indicates that the engine is turbocharged.

The B230 is a "low friction" version of the B23. Both are 2.3 liters. The 23 has a forged 4 counterweight crankshaft, the 230 a cast 8 counterweight 'shaft. 230 connecting rods float on the crank journals & are guided by the pistons; the 23 connecting rods are precisely machined to fit the journals. 230 has light, cast pistons; 23 heavier, forged pistons.

Result: better fuel economy, more power (at least in theory). I do notice that the B230 cars seem to have more pep than the B23's, even though output is the same (114 hp, 136 lb.-ft) on paper.

I believe that the '0' is added to distinguish between the two designs.