sup guys, im askin a question about a ZEX nitrous kit, this kit is off ebay brand new,. for 525$ it comes wtih a ZEX purge kit (100$) and a ZEX down tube (75$), i dont know how to install it and i havent bought it yet, just bid on it. Now, what i need help with, can some 1 tell me what a down tube is? What its used for? and basically how it works?, and i was also wondering how the shop that is going to install it is going to do it? i have a 91 civic DX hatch, and im wondering how they are going to do it? tap the ram air intake? or what?

THX FOR THE HELP