I am building a roller 350 here for next season. I'm trying to get the most hp I can n/a before goin to a blower. What do I need to look for in cam specs to make sure the cam does not cause the motor to revert. I am looking for 400-425 hp all motor. Specs on the motor will be a standard bore 350, aluminum heads, matching intake, 750 dp carb, then the cam. I might go a 383 bore size if needed.

Turning it into a 383 would require a new crankshaft with 1/4 inch more stroke.
Sorry, don't enough about SBC's to make a good cam recommendation. Just make sure the lob sep is 112 or higher to prevent reversion.

Yeah, I know what is needed to go to a 383, I just wanna make sure my cams specs I buy won't let the motor revert.

A key detail would be the exhaust you are planning to run. Dry exhaust would allow you to run all the cam you want, stock exhaust will limit you. I am pretty happy with my simple little 350 vortec I built this year, but it is relatively mild compared to what you are looking to build.

I would not pass up the stroker option if you have the motor apart.

Regarding reversion, there isn't a hard and fast be cause it depends on a lot of variables. Some of the stock Merc SBC cams came with real narrow LSA (109) which work fine for the shorter duration cams. For the power you're looking at I'd go with an LSA of 112+ and keep the duration at .050" to 230 degrees or so using stock manifolds or GLM style. With dry exhaust you could get away with more.

Crower makes some roller EFI style cams with 114 LSA.

How hot does the dry exhausts get? I never really looked into them as of now, I was planning on running the stock mercruiser wet exhaust.

Specs on your build? The motor I got in the boat now I built is a vortec motor as well.

Definitely stroke that thing!!!! I just built a 350 and now I wish like hell I'd have stroked it.

With stock cast Merc exhaust, you can't even upgrade the cam enough to make a real difference.
You also cannot make the best cam choice until you know which heads you are going to use and the flow numbers.

Dry exhaust does not get any hotter than wet exhaust. It is still fully water jacketed. The water just dumps out a separate outlet instead of mixing into the exhaust gases.

IMO, you would be money ahead and have a more reliable package if you just dropped in a stock Merc 454mag.

OK, well here is my 2 cents... The Crane HR-284 has been an excellent cam in my 350. My motor was built in 1995, a 355 with forged flat tops, SPS rod bolts, Dart iron heads, steel crank, fluidamper, Crane HR284 camshaft 222/230 in/ex duration at .050 with .509/.528 lift with 1.5 rocker ratio. My motor has some blue roller rockers not sure if they are 1.5 or 1.6 and still uses the stock 320 EFI intake and ignition system. It made 424 HP and 445 ft lbs torrque on the engine dyno with dyno headers on it (1 3/4" primary with 3" collectors if my memory serve correctly. I can not say enough good things about this camshaft. My boat is a 1987 Checkmate 19.7' Ambassador with 1.5 ratio alpha SS drive. With a 24 pitch off the wall brand stainless 3 blade prop it ran 72 mph GPS at just over 5400 rpms. I currently run a 22 pitch Rev 4 out of the box and it will just hit 70 at about 5200. This is with the stock MERC exhaust manifolds and risers with through the hull exhaust. I can idle along in the no wake zones at a very lopey 500 rpms ( almost acts like it has a little blower surge) or kick it up just a notch to about 700 rpms where it smoothes out a bit. I am not sure if this boat ever had headers or not, but it has been running with the stock manifolds since before I bought it which was in 2003-2004. If I do ever step up to a 383, I will either run this same camshaft or the next step up in this same line. I was sick when Crane went out of business but luckily the new Crane still makes this camshaft. By the way, I am not sure if it is a Crane grind or not, but the cam duration and lift specs for this camshaft are the exact same as the camshaft in the GM ZZ-383