You won't notice a darn thing. At best you might gain a couple HP. It also depends on the other parts of the engine; cam, compression, heads? Depending on how its set up, you could be going the wrong direction.
Air gaps don't make more power from a cooler intake charge because they reach the same temperature as non-air-gap, it just takes longer. During that longer warm up time you will experience a more "cold-blooded" operation.