Ok, all I'm at LOTO as we speak, had trip planned for months but never got to get the new engine broke in before this weekend cause the local river levels were all messed up the previous weeks, so I'm trying to do it here in the rediculous 9' seas of the Ozarks! So here is the run down: it's a fresh build, 0 hour, standard bore 454, with flat top pistons, new bearings, rings, double roller timing chain, ARP rod bolts, 0.564/0.567 flat tappet Comp Xtreme Marine cam, new lifters, bla bla bla. The heads are 2005 Vortec heads with oversized stainless valves, and a ton of nice port work. They have new custom springs matched to the cam, with rotators, new valve locks, retainers, harland Sharp roller rockers with poly locks, and after cc'n them, compression came right out to 9.1:1, and the tank is filed with 93. It has a just rebuilt Holley 850 sitting on a Port matched Weian team G intake. Has factory thunderbolt ignition, and factory mechanical fuel pump.... (possibly not enough? ) exhaust is CMI sport tube headers, with dry tails going into thru hull tips... I have a 24p Bravo-1 4 blade prop on it, as the old 330hp set up ran best with a 22p bravo 1, so I figured a 24p bravo on an estimated 500hp motor would be a good start. I unfortunately no longer have the 22p btw, and 3 blades run terrible on this boat. Oh, and yes the cam was broke in properly with good high zinc oil, and yes I do have the correct head gaskets to run a gen6 head on a MarkIV block.

HERE ARE THE PROBLEMS:
At initial start up it runs awesome, but after about 5-7 minutes you can smell oil, and it will slowly lose rpms. If you give it more gas it will just bog down and fall on its face. Pop the hatch and oil is EVERYWHERE. I have 2 breather filters on it venting onto the flame arrestor, but oil is still all over, ( possibly coming out of dipstick? ) and if you take the breathers off while it cools down, white smoke comes out and smells terrible! ) it will start back up but you gotta pump the throttle to get it to fire. It is burning oil and smoking out of the starbord tailpipe on initial startup. I've tried moving the timing from 30-35 with no change really, but seemed better at 30, but now when you turn the key off it keeps ****ing running! It's using as much oil as gas and 5-7 minutes of good run time is just enough to get you stranded on this terrible water! Im done for now, It's too dangerous out there with a broken boat. Any ideas anyone? Btw the oil pressure and engine temp gauges are reading good.

My first thoughts are bad valve seals and a fuel issue? Too much carb, not enough fuel pressure, something like that? Our maybe I'm on the wrong track and it could be a coil overheating and bran new broken piston rings? I know for a fact that they were installed with the correct sides up and the gaps staggered... idk, any input would be amazing. Thanks guys!

make sure oil level isn't too high. some boats need to be at or just below add mark cuz of wave action sloshing oil. other boats need to be filled high cuz of sloshing oil missing pick up and pressure dropping with each dip of the bow. broken rings and oil smokes right out the exhaust. same same with valve seals. yours is leaving the engine, either thru breathers or a gasket leak if u see it on outside of engine...do you have a big vacuum port on carb? mebbe try installing a PCV valve. ok, just reread problem section of first post. how much blowby when engine is running at startup? how much more when warmed up and running like chit? unless loose oil is going into flame arrestor and fouling plugs and smoking, (which is possible) it could be a ring clearance issue. get a gallon jug and fab up a puke tank. run the breathers into jug and another breather out to flame arrestor. heck, tie wrap jug so open lid is right next to arrestor might even work. see if getting tonsa oil into tank.

If the oil is concentrated at the rear and very oilyon the transom somebody may have put the rubber gaskets on the front and rear where intake meats block. Notorious leakers if you use gaskets there, permatex only. Hope it is that simple.
On the bright side, look how much fuel you are saving. Good luck

Losing power, having to pump the throttle, and puking oil is usual ya very bad sign of a compression leak into the crankcase

It's Definately appears to be puking oil at higher rpms, not idle, and I guess the carb ingesting oil through the breathers could be what's causing it to smoke so bad... but it seems like it's even worse then that.. I guess I could try the puke tank idea and see if that looks the smoking, but it pushing that much oil out is the problem I wanna fix, not just bypass. Compression leak into the crankcase is more along the lines I was thinking. It seems like broken rings or bad valve seals , (both new btw) would be the most likely culprit, with bad valve seals topping my last, cause of the huge smoke show out the tailpipes on startup. Bad rings would allow the oil to just leak back down to the pan, but bad valve seals would let oil leak down onto the top of the pistons and be ready to burn off on initial startup right? And the power loss after 5 minutes if cruising, Any thoughts there? I feel like it may be over carburated? But that shouldn't cause problems after a certain amount if run time, It would be all the time right?

Was the windage tray re-installed when the motor was put back together? Is it over filled with oil? What is the oil pressure? My motor doesn't have valve seals and it doesn't use oil or smoke.

Has the same oil pan/filter set up as before, and the oil pan has a built in windage tray. Isn't overfilled with oil, and has good pressure. 30-40 pounds at idle.

Did this happen as soon as you started it up or after you hit the 9 footers. I've seen the windage trays break off stock pans before. What is your oil pressure hot?

why dont you take your compression? or even better with a leak down test! I would start there...