What you can do is kiss the edges of the intake ports to smooth them out... All you are really doing is to smooth the edge out so you have no sharp edges... Also like it was mentioned match the ports of the lower intake to the heads..
Even doing this on an NA makes a nice difference..
And the compression will stay the same unless the heads have been shaved to remove any unevenness, in that case you may have as much as .5 in compression added to stock.. But we haven't seen many instances where this was required on a 3300 or 3800.. But it is possible..
If you have 9.0 to 1 compression you should see compression in the 180-190psi range iirc.. I think if you are 8.5 to 1 in good shape 170psi should be easily attainable... But keep in mind this doesn't always ring totally true.. And its hard to know if the heads were shaved, and how much was shaved off if they were shaved..
But a good compression test would let you know how the piston rings and valves/ valve seats are
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