I have a 1989 Baja 226 Sport with a 454 +.030, 088 heads, hyd roller 230/236 .587/.612 112cl, holley 800 on a dart manifold and Aqua Power Semi-tuned exhaust thru hull. I have Bravo 1 with a 23 mirage prop. The motor seems to labor until the boat is on plane. It seems to have a slow speed miss. Once the boat gets on plane. it screams. It seems to run better above 2500 rpm. What could be the problem at slow speed? Is it the rect port heads? The carb to big? Thanks in advance for your help.

How low is low speed miss? Does it idle properly? Where is the carb from? How is it jetted?

If you have short riser/tailpipes, it might be reversion.....

Just my opinion, but the size of cam, rectangle port GM 088 heads, and Dart single plane intake manifold seem a little large for a 454cid marine engine and isn't likely to perform well in the user friendly RPM ranges a marine engine usually operates at---that's why you are kinda "soggy" out of the hole.

A smaller, oval port design head, dual plane intake manifold, and a smaller duration cam something like 224*/230* would most likely perform much better for you-----and that's with a good aftermarket exhaust system such as a Stainless Marine, GIL, or something close in comparison.

Also, I have never heard of "Aqua Power" brand exhaust systems...so, you could have a bit of a reversion problem as suggested---especially with the size of cam you're running.