If your talking about a tb spacer, they get a bad rap. They do work on some applications. They make a slight difference on jeep inline engines for one. AEM dyno's thier intakes with and without a tb spacer, if there is a benifit with the spacer, they ship it with the intake, if not, they don't. If a spacer would even make 1 or 2 more hp, you wouldn't feel that with a butt dyno, but thats 1 or 2 more hp than you had when every hp counts. I don't know if the spacer helps on the 4.6 or not, but don't totally write them off as they do work on some applications. You may even find that some parts may show nothing on a dyno, but yet improve throttle response and such. There has been alot of R&D spent on spacers my airaid and others, unfortunatly one size doesn't fit all as they market them. It's been an old hotrod trick for decades with the carbed engines, however, FI is a different beast and benifits can be hit and miss.