The base Performer (not talking the Performer RPM/Air Gaps here) probably would get beaten by a factory intake on the dyno- their ports are kind of a compromise between the 273/318 size and the 340/360 size, so Eddy could offer a "One size fits all" manifold for the SBM. It was intended as a replacement for the LD340 (and the D4B/LD4B), but doesn't really live up to either of them, in my humble and somewhat biased opinion. The only reason I would run one is if I didn't already have a 4 bbl. manifold, and just wanted a nice street 4 bbl., which they are. Although I'd be hard pressed to pick one of those over, say, a Weiand Stealth. Just personal preference there, though. The Performer AG would be a different matter entirely.