The first two letters denote the engine series/type. KA, SR, RB, VG, VQ, L, QR, ZH, VH, etc.
The next two numbers denote the displacement (in liters) of the engine. 24 is 2.4 liters, 30 is 3.0 liters, etc.
The NEXT letter (either blank, D, or V) denotes the valvetrain. No designation means it is a SOHC engine, D is a DOHC engine, and V is Nissan's
designation for variable valve timing (aka VTEC in Honda terms), plus DOHC.
The next letter denotes the fuel delivery type. A blank letter is carburetor, E is Electronic Multiport Fuel Injection, and D is Direct Injection. There is also "i", which stands for Throttle Body Fuel Injection.
The last letter(s) denotes forced induction. A blank letter is naturally aspirated. T is for turbocharged applications, with each turbo using one "T".
Twin turbo's are TT, and triple turbo's (if it was ever made) would be TTT. Supercharged applications are noted with a R.