But you didn't just add boost Bill, a free flowing exhaust (especially with your header) an intake and big four barrel, a cam, increased compression, and a ton of lightening has also helped. A slant six with these mods won't feel to lethargic at all, and then you crammed almost 70% more atmosphere into it.
If you were to use an example of just adding 10psi to an engine, Serj's would be a better example.