Boost drop when adding heads/cam

[slither1]

Okay, this seems like the best place to put this. I am a member on supraforums and this guy and me are having a debate on boost.
I said when you add heads/cam(s) your boost gauge will read lower with the cfm staying the same. He says

If your theory is correct, see if you can find any centrifugal supercharger guys who have had boost pressure drop, after having a cam installed or headwork done, with all else being the same. I know you won't, but go ahead and try.

I know what happens and I have had it happen to me. The gauge will read lower. I added an s-trim to a stock mustang a long time ago. Boost was at 8psi. Added a set of heads and a cam, and even though the car made an assload more power, boost fell to about 5-6psi IIRC.
Thanks in advance, hopefully he will reply in here himself.

[pavement pounde]

You are letting the engine breath better so the internal pressure drops but the hp goes up

[speedytang]

Boost-PSI is a reading of Back Pressure so if you have better flowing heads your going to show less boost on a gauge which is really a artificial measure anyways. Cam will do the same thing because of lobe separation which might hold the valves closed longer which will increase you gauge reading or the cam open the valves faster and will show a drop in pressure. A turbo gauge is for showing off that you have a big number but means nothing in power production since the basis of the number is on Back Pressure.