there are a few ways to do it, the simplest is clipping a couple wires, I'm not sure which ones but a search might help you find that out.
http://www.240sx.org/faq/index.html I found this on the 240sx.org faq page (which btw someone should change the name of to "articles" or something because no one ever looks there). If you want just the rev limiters taken off follow through the second paragraph or so. Basically stop where he says what you're doing will disable your speedo.
Actually, I take some of that back, read through the ENTIRE article from top to bottom and then decide what you want to do, as it appears some people have a little trouble with some of the methods.