Whats your power goal and psi your running? it would be ideal to size the intercooler to your power output. But to answer your question the ebay full piping kit is good for fabbing up your own route of piping but would be best if you also got the intercooler piping welded together;to limit possibilities of leaking through coupler. And most people go with 2.5" piping but if your on low boost with smaller sized turbo go with 2"