a downpipe is used to route the nitrous lines under ur car, u tap into the intake about 6 inches in front of the manifold. go to zexs web site and read up what ur getting urself into. look at their dry kits, u dont want a wet kit, and direct port just involves 4 injectors installed into the manifold runner instead of just 1 in the intake. id strongly suggest switching to mpfi b4 running nitrous