Cylinder Head Porting and Power Production

rmchrgr...... I would invest in a dyno session at a different facility before spending a pile of money on new heads.

Maybe I’m thinking of a different situation, but I seem to recall you had mentioned some unwillingness to do much tuning at the facility where the motor was tested last time.

I remember thinking I def wouldn’t be taking those results as “gospel”.

If the fuel flow numbers are accurate...... it’s using way too much fuel.
For comparison, I grabbed a dyno sheet for a street 446 making about 50hp more than your SB, and at 6200rpm it’s using 20lb/hr less...... and has a 12.8:1 a/f ratio with a bsfc of .479.

So, either the tune is way off...... or the combo is really that far off(or there’s a problem with the dyno room causing low power output).

Edit- found one more similar to yours:
416, RPM heads flowing 270-ish, [email protected] solid cam, SV intake with old school 850.
561hp@6200, 246lb/hr fuel, bsfc .46