No you don't have to. The heads are the biggest part of the intake system. We port the lower mani quite a bit to get it to port match but we won't do it unless we have the heads too. The whole system works this way. The closer to the engine you are, the bigger that item will be. Nissan wants the system to step down and not step up killing the air flow hitting a big lip. When we sell our kit we port match everything so there's no step in either direction. I think we'll at least start gasket matching the lower to head though to get more air in. My lower by an older porter left a good deal there. I've got a good 1/16-1/8" that can go!
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13 370z-
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