Wolf -I think the stock 1.6TD airbox is close to 2.5" diam. at the outlet (...and just about the same as the black fitting on the manifold). I've trial fit a silicone connector to leftover 2.5" aluminum intercooler pipe that will likely be used to connect to a 2.5" K&N cone filter as I don't have a stock 1.6TD airbox available. Where/how are you locating the fuel filter with the new manifold? I'm putting the non-EGR version of that manifold into a 1982 caddy and will be moving the filter to just fwd of the passenger strut housing & looking for some photos/ideas of best way to do this.