Difference between turbos

This is a stupid question to gurus of cars but i have been learning alot about them but am still new. What is the difference between like a t3 and t4 turbo. Im thinking it might be size? Also can you tell me the different types and in your opinion or fact which is the best for my car. I have a 99 acura integra gsr (b18c vtech). i was told my compression is 9:1 but i went to a sight that has a compression calculator that said it was 10.24:1....oh well. It has a tokiriko intake, skunk2 cam gears, edelbrock intake manifold, clutchmaster stage 3 clutch, spitfire ignition wires and spark plugs and aerospeed exaust. I heard most of my crap i would have to take off when i get my turbo to get better performance is this true. Last question is the engine sleeve the peice on top of the motor that says vtech on it. Please everyone who has info please tell me cuz alot of people look at a subject but never respond...thank you.

Okay dude, however told you the GSR had a compression ratio (c/r) of 9:1 is smoking crack. The USDM GSR B18C1 has a 10.0:1 c/r. That's first off...second T3, T4, T3/4, etc...refers to the size of the housings, the compressor housing, the turbine hosing and turbine, etc. The bigger the number, the bigger housing in general. This means the turbo has more airflow capibilties, which in turn means it can produce higher power output numbers due to the higher PSI the turbo can provide (if the motor is built to handle such heavy boost). Bigger turbo's can produce more power, but have much more turbo lag. Smaller turbo's can't produce as much power, but have less turbo lag. Now, it is impossible to tell you which turbo is best for you. It all depends on your goals, your end goal for power output, how much boost your motor will be built to handle, how much airflow is needed to reach your goal, etc. A turbo that is right for one set-up may be dead wrong for another set-up. Now, a stock GSR block really can only handle about 8psi, so keep that in mind. You should be able to keep your skunk2 cam gears, edelbrock intake manifold, clutchmaster stage 3 clutch, and spitfire ignition wires. You'll most likely want to run colder plugs though. Also, depending on the size of your exhaust, yes, it will have to go. It is most likely 2 1/4" piping, which is too small for a turbo set-up. 2 3/4"-3" is better for a turbo set-up on that car. Also, the intake will go. It will be replaced by piping from the turbo to the intercooler to the intake manifold. A seperate intake goes to the turbo where the air is compressed, and then it follows the above path. I hope this answers some of your questions and helps.