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Allowing the engine to breathe freer, especially at higher engine speeds, is a redesigned intake system including a new intake duct and more significantly (and expensively) a new inlet manifold that is shorter and wider than before. As if that were not enough, Nissan has added new pistons and a revised inlet camshaft profile. These changes are complemented by variable valve timing on the exhaust side as well and a new timing chain and oil pump. Other bits and pieces have been lightened and stiffened to cope with the higher engine speeds.
Taken from:
http://www.carenthusiast.com/reviews.ht ... le&id=1235