Ok, I'll get the hard part out of the way, cracked block on 454 mag mpi over the winter, the pain is still sharp ....

Now the good part, chance for repower !!!

Boat is a 27' eliminator pod-cat, engine is the stock Gen 6 (1998) 454 mpi mag w/ 5# procharger. Has run great, correctly modified fuel system for procharger, thanks Smitty & Tyler for all your post

Will pull motor next week. Several options, buy replacement block and off to machine shop for general reconditioning, or ... consider the GM performance short blocks below and save time.

GM # 12498778 = 454 w/ "mag" forged internals
GM # 12568782 = ZZ502 w/ "mag" forged internals

I'm interested in bumping up to a 502 but want to make sure the rotating assembly is as "drop in" as possible. Looking at schematics (parts list) for the MERCRUISER 454/502 Gen 6 mags I see all part numbers the same except for pistons & crank. I'm concerned my balancer and flexplate (flywheel) might not work on the GM crate 502, or the 454 for that matter. It would be sweet to use my "old" balancer & belt pulley arrangement.

I'm open for all advice, hopefully some day I'll pass on some useful data, until then excuse me while I continue kicking myself in the azz.

As long as the new short block is 1 piece rear, your balancer & flywheel will work.

"Itsgood", thanks for your feedback, it was good and opens some options ...

I've seen on some fourms here that folks are concerned about the "crate" engines. From what I can tell by looking at the product specs the GM 454 and ZZ502's are basically "Mag" shortblocks. Add cometic head gaskets and away I go .....

Concerns anyone? (critique appreciated, because I don't know what I don't know)

Thanks

nothing wrong with the right crate engine...just change the cam...suggest you call Bob @ marine kinectics..he will dial you in as far as valve train is concerned

I feel your pain. I cracked my block years ago.
Im sure some people had luck with them but I went the GM crate route short block 502 way. I ended up snapping a rod and blew a piston apart in it. If I had to do it all over I would of started with just a block and bought H beam rods and good pistons, basically bought all the better pieces myself. Thats what I did after it let go. Get a block and buy a decent rotating assembly. This way you will feel more comfortable when you want to up the boost.
I think I had to change my flywheel. Balancer came with the short block. Also will need new oil cooler adapter, should change oil pan.

I have a 2000 454mag long block that I would make a deal on if interested

Thanks for the input ......

Jury is still out, but will likely be biased by a ticking clock.
Doing a rebuild is my preffered route, but a crate sure is quick. Manic winter waiting for boating season .......

Any advice on best oil pump for a rebuild that will use a "non-self contained" (oil from engine) procharger?

I noticed my old style M1 knock the pressure down by about 10psi.

Thanks

Go for the new GM shortblock. It is very likely, by the time you get another block, have it machined, assembled, etc, you won't be far off from what a new GM one costs. Then, you can keep your old rotating assembly for a spare.

Plus, this time of year, having one shipped to your door in a few days beats waiting several weeks on a machine shop.

http://www.gmpartsdirect.com/results...umber=12498778

x2

Change the camshaft and any steel freeze plugs for brass in the ZZ502 block for sure and if your 45 has a counterweight on the flywheel and balancer, make sure the 502 has the same before you install yours other wise the stock internal balancer on the 502 if its there will accept your pulleys and the internal balance flywheel (without counterweights) are easy to find. DON"T put external balance (counterweighted) balancers or flywheels on internally balanced engines that come with internal balance flywheels and such , you will destroy the rotating assembly and the engine. The forged internals of the ZZ502 should take mild supercharging just fine when the air fuels are adjusted correctly and just use a .060" Cometic gasket min. to keep the compression in line.
Also keep in mind that GM performance standard engine or block warranties do not cover that part when used in marine applications like they do for the same part in vehicle use.

Best Regards,
Ray @ Raylar