Anybody know what's inside the 89' 454 mag motors?? Crank,rods, heads etc.??

The 365 Mag has forged crank, "white" rods with 7/16 rod bolts, forged 8.75:1 pistons, 4-bolt block, rectangular-port heads with 2.19 intake and 1.88 exhaust valves, standard GM rocker arms, Winters'-design aluminum intake with brass water passages, anda 224/224 [email protected] lift, .510/.510 lift hydraulic camshaft.I understand that Merc called some of their low-horse motors "454 Magnum" also, in which case it's a 330 horse motor.

If I am not mistaken, Mercruiser released the 365 H.P. Mag motor with the introduction of the Bravo drive in 1988. I think "Mag" motors before 1988 were 330 hp. oval port, cast crank...etc...motors.

1987 454 mag was infact nothign more than aplain jane 330hp 7.4. I know i have one. It is notw sitting in my garage and being replaced with a real 454 mag with a big fat blower!

OK so really nothing worth totally rebuilding, and trying to get 450 hp out of. A buddy of mine has a set with about 450 hrs on them and was wondering if he should rebuild them or upgrade---boats a 89' 34 scarab III.
Probably best to start out with a set of 502's

you already have good parts in the motor. thats a baseline to start. doesn't take a whole lot to get 450 hp., beside if you get some 502s you might have to work on them also and add more expense

if they have the square port heads and forged internals yes they are worth rebiulding. I am gettinga rebiult long block 454 mag and having it setup for a blower. Bruce is biulding it. If i get eth bigger blower and the intercooler he says 600hp should be easy to make.

with the smaller blower an no intercooler 525-550 is reasonable.

Clean up the heads with a bowl port add a little compression cam intake and carb will get you to 475 or so. 10.0 compression big cam and a good intake and carb you get 500+ the next step is a blower or more cubes.

Even the 330 motors are worth upgrading as the bottom end is extremely reliable to 5500 rpms. And JimV has been doing the stock oval-port heads so that they can breathe. All in all, the 330 is a very good base to start with if your horsepower target is under 500 hp. Dyno has what he refers to as "330's on steroids". With all Federal Mogul parts in his engines he's making around 470 horsepower. He did put Merlin oval-port heads on though. SuperV is making 500 hp with his upgraded 330's, also with Merlin oval-port heads.