Regarding Pop Charger: What is the actual effect? I've seen the dyno chart that shows a HP gain at 4800+ RPMs. I get that's a good thing when winding it out. But besides a whole lot of noise under the hood, does it buy you anything at lower RPMs? Will it help with any extra power off the line?

And are the gains from a plenum spacer additive? (together with Pop Charger)