FWIW, the 4bbl intake is much more efficient than the 2bbl is too, it alone will help efficiency, not to mention the increased flow of adding a carb with more venturi area.
In a dirt track car that required cast iron intake and exhaust, as well as a 2 bbl carb, we found that the 4bbl intake adapted to a 2 bbl always ran much better than factory issue 2 bbl intake, I'm theorizing that the larger plenum volume helps too over the much smaller 2bbl plenum. So in addition of less restriction of going to a 4 bbl carb, the intake is a much better design.
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Brad Yost
1973 T/A (SOLD)
2005 GTO
1984 Grand Prix
100% Pontiacs in my driveway!!! What's in your driveway?
If you don't take some of the RACETRACK home with you, Ya got cheated 
  
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