We recommend the Aquamist HFS4 and it is the only kit we've chosen to recommend and carry over the years due to its superior funcionality and quality combined with a trunk mounted tank. We've tuned countless N54s with meth injection on the Cobb platform over the years with consistently great results. If you google or search this and other forums you'll find plenty of examples. Let us know if we can help at all:
support@protuningfreaks.com.