Anything mercruiser built from 1988: 454 MAG and Bravo would be rated at 365hpat the crank and 350 at the prop. IF its a 7.4 litre and Bravo then its not the mag motor which means its 330hp at the crank and 310 at the prop.
--IF it was a 1987 vintage then you would see 454 mag but would have an alpha drive and be rated at 330/310

Old wellcraft sales brochures list the 7.4 330hp as 295hp at the prop and the 454 MAG 365hp at 360hp at the prop. Not arguing just saying that prop shaft hp numbers tend to vary depending on where you look. One thing for sure is the 365's are runners and the 330's.....well not so much

my 91 454 MAGS carbed are listed at 385 per the manufactures spec sheet from fountain.

Merc never made a carbed 454mag with 385hp. The carbed 454 mags were 365hp and the carbed 502mags were 390hp.

then maybe fountain did something, because their build sheet I have says 385, if you go to nadaguides it says stock equipment is 385 and when my insurance rand the sn of the boat they told me it had 385hp engines.

My point exactly! But I agree with Griff the 385hp was the later 454 Mag MPI with 385hp at the prop. I would guess the NADA guide made an error.

Close.
The 1989-1991 454Mag carb was 365/350.
The 1990-1991 502Mag carb was 410/390.

As far as the Fountain with 385hp 454Mag, it's a typo. Period. Fountain did not do anything to the motors to change the manufacturer's hp rating.

yeah I dont know, it might be. everything Ive had and even when people worked on them said their 385hp, so who knows, not like the 40hp difference probably makes a difference either way. I was thinking maybe the gill exhaust helped but I doubt it as its still manifolds on there vs headers. It just seems odd multiple places all say 385

maybe your carbed mag 454,s make 20 hp more than all the rest of them because you used 92 octane fuel,maybe reggie tested them that way,il bet he dyno,s every merc engine they installed in their boats.

Gil manifolds DO help.
They probably are good for 10hp on a 454 Mag, and maybe 12-14hp on a 502Mag.

That puts your 454 Mags at maybe 375 instead of 365, but it technically doesn't change the ENGINE RATING.

Not sure where you're getting the 40hp difference, though unless you're counting the drop from crank rating to prop rating.

It's really irrelevant if you plan to add hop up goodies. Once you change the cam, do some port cleanup on the heads, bore notch the cylinders, and zero deck the block you're going to be well over 400-430hp. You have a good motor to start with.

Just be glad it's not the 330 version, which has weaker bottom end and poor flowing heads.