Low boost?
It might be similar with the compression ratios and chamber sizes of the heads...
Boost sort of measures the restriction of your engine. Think about blowing air through a skinny straw and a fat straw. You can blow more air through the fat straw with less restriction (lesss boost.) With the small straw, you have to blow much harder to get the same amount of air through (more boost.)
What really counts is how much air you can move through the engine. More air and fuel mean more power!

