Simply offered as an FYI reference, I have been using a 221/230 @ .525/.545" on a 114 LSA hyd roller cam in a 377 (Crower cam) with no reversion issues. In my estimation this cam is near, but not at the limits for stock wet exhaust in a SBC.

Hell yeah! Will that make my boat jump a Coke can?! 🤣

Honestly, I had planned on swapping an L92 in. But the LS swap community agreed that the 383 is an excellent marine engine, so I thought I’d explore options for getting more out of what I have. I know how quickly a build can rack up a bill, so I really wanted to leave the rest of the valvetrain alone, if at all possible. There are also some cost friendly aluminum heads local to me, but I have no idea how much the machine shop bill would be to marinize them.

If in the end there’s no way to do it without dropping massive amounts, then perhaps a custom calibration would be the only thing I’d do in order to make sure it’s running its best.

383 Mag’s don't come new in boats but are available ‘over the counter’ . It is from Mercruiser.

Anyone know the cam specs / valve train specs ? All i can find mentioned is roller rockers.

I know most of the 350's came with that GM 395 cam (288 int./308 exh,, 0.431 int./0.451 exh., 109 LSA , and the 377 Scorpion had the 222/230 .510/.530 114 LSA. The cam for the 383 MPI likely falls somewhere in between these two. I can't find the part number but it is possibly around these specs Cam Specs: 215/220 @50 .457in/.474ex 112LSA

Small block chevys don't make any power in marine applications. You're just wasting your time.....

Not sensing sarcasm, but if you are looking for 400 ish HP SBC will do the job. More than that gets problematic if naturally aspirated.

Trash,
The sarcasm skipped past you then... Do a search of OSO with my username if you want some marine SBC tech.

Nonsense. Sounds like a friend of mine who swears it’s big block or nothing. I smoked him with a naturally aspirated 346” LS.

My boat came with a 350. The 383 is plenty for it, even if I leave it alone.

If you didn't pick up on the sarcasm, you might want to check out this thread.

High powered small block alpha