did you by chance dry the exhaust up? obviously this is unrelated to what happen with the rocker however I noticed you had the stock exhaust. if you went to a more duration camshaft you could be sucking water back at idle.

OK, I'm admittedly a newb when it comes to making these boats go fast. What do you mean by dry the exhaust up? By the way, aftermarket exhaust and hydraulic steering are on my list of things to address.

While we're talking about engine stuff. What do you guys think I could do in the winter to get up in the 500-550 horsepower range with my 454's? They are 330 bottom ends with 2.18 intake valves, and 1.88 exhaust valves. Edelbrock air gap intakes, holley 750 marine carbs. I want to run 70+ Here's my cam card..

with the stock exhaust you have the cams can create reversion. (suck water back into the cylinder head ) to avoid this you should extend the exhaust riser so water is not exiting the so close where the vacuum will pull water into the cylinder head and valves . a bravo style gil exhaust with the hp 500 cam would suck water back into the exhaust. search gil exhaust images and where the end of the stainless pipe is would be where water is introduced. and that carburetor package would still pull water into the cylinder head

do you have oval port heads or square port heads? if you have the small oval port cylinder heads replace them with square port heads change the exhaust and a maybe a 236 intake and 242 ex @ 50 camshaft is close to what the hp 500 engine used

500- 550 hp with a 330 base is impossible. you need at least the forged bottom end to upgrade the top and increase HP with reliability... I'm no pro when it comes to engine building at all, but I know that for sure!

yeouch, I was hoping to keep my oval port heads lol. I just had the bigger valves put in them. Does anyone run aluminum heads with the raw water cooling in fresh water? Would that be easier to get the horsepower than to buy square port heads and have the larger valves installed?
With the Gil exhaust, are you talking about the risers only, or the whole thing? I want to replace the whole exhaust at some point but was wondering about just replacing risers for now.

Yeah Jeff, I was figuring I'd have to change over to the forged bottom end this winter anyways, before I do much else. 750 cfm carbs prolly wouldn't flow enough for 550 hp either would they?

These are the 353049 casting number heads. I was thinking they were ok for good horsepower. Maybe I got bad info?

They do have a stock extended stainless riser you can put on. Boostpower usa has them and a few other companies .
As far as the bottom end goes you can use the bottom end that you have it is not impossible. However being cast it is not as durable as forged. I would not go more than 500 hp.
I am using edelebrock aluminum heads in the chesapeake

Those are 049 heads. Best of the large oval port GM heads. Bigger valves, seat work, a little work inside the ports around the valve area and they can support 500hp. I run that exact same head and with roller comp cam (sorry, I don't remember which) Dual plane intake and holley 750s and made 502hp on one and 510hp on the other, all under 5800 rpm.