Originally Posted by josh@z1

Z1 hearers are the momentum Headers only we changed the head flange for the logo and a more economical cut which allows us to bring them at a lower cost to you guys than Momentum ever could. They are still made by the same manufacturer that built the others and it is obvious the quality is equal. All comparisons we have done between the Momentum headers and the Z1 Headers have yielded identical results however our modified plenum has yielded much better results than any of the other plenums available for the VQ37VHR. The 400hp package is just that. We have made and continue to make ~340rwhp with this setup (with other supporting mods) which, accounting for a 15% drivetrain loss, equals 400 crank hp.