Here's
my fully adjustable LSD tutorial, IMO the best LSD
. There's also the old way of doing it when you fill an open diff. (the gear one) with thick grease (It's never worked the way it's supposed to for me.). It's technically not an LSD though.
For some reason people feel they need to make real car analogies when talking about these. I think your talking about a FET upgrade (or a FETurbo as some people call them
)...you either have to stack them or somehow get two bigger ones on there (one for forward, one for reverse). You have to be damn good at soldering small surface components if you want to do it yourself.