Any Dyno numbers for forced induction (Turbo or SC)... this manifold vs. plastic stock?
At this time, we've yet to do a back-to-back comparison on a boosted Slingshot application to show a before/after result. On other Ecotec applications, we've seen a 10 to 20 HP gain boosted, with a concurrent smoothing out of midrange torque due to the shorter runners, which helps to improve traction on the traction-limited Slingshot.
Here is a dyno graph from Greg Hartman's Slingshot that we just completed. While it's not a before/after, it helps to show how the manifold really assists the upper RPM range, with usable power all the way to 6800RPM: