Originally Posted by Caballerokid
The rpm air gap won't make a difference accept at high end.
Ummmm, not true. The RPM will make more power throughout the range over a standard Performer. In my opinion, all you're doing when you replace a stock cast iron intake manifold with a Performer is reducing the weight on the front end of the car. While that's a good thing, it's a fairly expensive way to reduce weight. Best intake manifold idle to 6000 is an RPM or other dual-plane, high-rise intake manifold.
Gen I SBC with conventional heads (not L31)
Professional Products 52020 Typhoon
Weiand 8016 (out of production, but can be found used)
Holley 300-36 (out of production, but can be found used)
All these high-rise intake manifolds were patterned after the aluminum Z-28 302 CID intake manifold that was cast by Winters for GM in '68/'69.