That's a question that nobody's going to want to answer because it's too big and we don't know what you want. Plus you obviously haven't done your homework yourself. So you need to start doing so and read these; they will give you your answers.
what kind of it legal things can i do in my integra 1995 , with out opeing up the engine? also whta types of exh are you guys running? strait thru?
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The rules that Ruck linked to are going to tell you what can and can not be done.
If you're looking for HP without opening the engine, you're going to be fairly limited. Some sort of "high flow" filter on a tube type intake, a header, and a lightweight highflow exhaust. Theoretically, you could do engine tuning and upgrade to a tuneable ECU but that seems a bit silly on a stock engine.