Enough air?
 

I'm surprised with 600+ hp that I'm only getting 5100 on both motors with a 26 lab bravo 1's (trs). A friend with similar configuration runs 28labs at 85 mph all day. The air holes seem small in the engine compartment. Am i on to something? Dialing has just started I reckon. That's the fun part anyway.

Similar does not mean the same. Slight changes can make a big difference. Without more details on the boat and set up, its near impossible to give you advice.

Lift the hatch a little and let it get a little more air. If the RPM pick up then you are starving for air. I added Ram Air to mine picked up 1-2 MPH. Also if your still using the stock arestor that could be holding you back also. You need a big one, check the CFM ratings.

OK, let me revise the recomendation. Do not crack your hatch if there is any way possible it will fly off. Maybe remove the hatch and then run it.

Just remember that if you crack the hatch and the opening is toward the front of the boat (most do), it will blow off if the wind catches it.

The boat is an older 30 velocity, weighs 7200 lbs. the engines are 509 cu 600-610 hp, trs, 26lab bravos

there are boats out there that cannot supply enough air to almost stock big blocks, so yes you may be on to something, not to mention on a hot day the engine are breathing extremely hot air..not good, so anyway to get them to breathe cool air is a +