I am still new to the whole car scene. When people are swapping motors, I hear things such as a b20 Ls vtec and a Gsr head. I don't understand how do you know which parts will fit? and is the b20 ls vtec the actual engine and the gsr head is an addon? Does the gsr head provide extra HP? What about a bottom block? What does that help perform in the car? And also why are there different tranny's? Please help me understand because I can't find a clear definition.. I've google'd it and searched it. Please help.