Great thread. Glad to see informative posts, without bashing and arguing.

I agree Very Refreshing!

Yes , I was starting to think these types of threads were gone forever . Great conversation , great information ! I'm all ears .

no bashing yet because the bashers have not found this thread yet.

Well don't incite them! I've lots to learn still!

My experience on a blown motor is put the best flowing heads your budget can afford. The more the heads flow, the less boost required to achieve your HP goals. I have upgraded heads on motors where everything remained the same except head port size/flow and experienced that boost went down at higher RPM and HP went up proportionally. That said, I agree that under most circumstances you cannot overhead a blown motor in a boat application unless the motor has an seriously undersized blower (blower is too small for the displacement). All componants do need to compliment and support each other.

dan,while combustion chamber is important as gm learned in the 60s,the best combustion chamber in the world will not cover issues caused from crappy port design.im not busting your balls im just stating facts.the pic of your heads looks good and im sure you are giong to see improvement ,your head guy did a really nice job.

1.5"Hg (vacuum on your guage) = 13.96 PSI actual
because
Normal Atmospheric pressure (O vac and 0 PSI on guage) = actual 14.7psi.

2 pounds of boost on your guage = 16.7psi
5 pounds = 19.7psi
10 pounds = 24.7PSI

You would only have 14.7psi if your cylinders were a perfect vacuum. You'll only have some differential pressure, not 14.7.

Yes! What you're seeing here is how different physical properties make the readings deceiving. Common logic is more boost = more air, and that's a bit misleading. More boost = more resistance to flow.

In your case your flow path became more efficient, thus lowering resistance to flow.

Beware, engineer ramblings below-

How come we (uhh, I mean those that have forced induction) monitor boost when we could be monitoring mass air flow? Obviously the technology exists... This would really only be good for testing, as once you have the runners/valves/cam dialed in, theyre not changing. Ambient pressure, especially for those on the sea, is pretty close to constant. Temp is almost moot.

You'd use a MAF setup to do real time flow testing of blower/head/cam combos, derive some constants/coefficients for the setup, and have a pretty damn good baseline.

I dunno, maybe people do this already,