Does anyone know what Mercruiser uses for internals on their engines; say a 260 hp 350 from 1990? Do they use Forged vs. cast cranks, pistons, rods? Did a search on this forum about marinizing street motors, and found out about different clearances on the ring end gap. Would a gmpp 350 hp 350 short block hold up with powdered metal rods, cast crank, cast pistons? If so would it be worth my while to pull it apart and redo the ring gaps, oil pump, etc? Or just rebuild my old one with forged goodies? Don't want to get to crazy, I only have an alpha to break. I"m a sensable driver that doesn't spend much time at WOT, usually just cruising with the family unless the weather is turning bad. Would be nice to have a little extra power (350-375) once I'm on plane just for that reason though!

I ran a SBC with cast crank and cast pistons in a1991 21' seebold eagle for a couple years. the engine was stock pushing an alpha outdrive with a hydromotive 28 pitch prop, ran 75 mph. It was a dog out of the hole so I tossed on a weiand 144 and ran it for another couple of years with no problems from engine or outdrive. That setup was awesome. I have heard alot of people say the alphas can't take the abuse but I am here to tell you that if you are gentle out of the hole you won't have any problems. As for the 350, I am not sure what it was out of but it was definatly not a marine engine. Best run was 87 mph on GPS. That

First, Mercruiser does not install internals in stock GM 350 powertrain engines they bring in by the rail carload from GM Powertrain. They take the GM 350 HD standard engine which comes with cast crank, cast pistons and standard forged rods and they install their accessories, manifolds, etc and paint the entire engine with polurethane black paint and deliver it as a mercruiser engine.
You can purchase a new long block GM HD engine part # 12499529 from GM Parts direct.com for about $1900 plus freight and install new brass freeze plugs, your current starter, alternator, intake manifold, exhaust manifolds, filters, coolers mounts ,accessories, etc and Whola, you have a nice new 350 marine engine. Should provide you with the same level of power and service you received from the first engine provided all your transfered items are in good shape. Don't skip if some of those items , especially exhaust manifolds and risers are getting to end of life as they can fail and cost you a brand new engine !
Hope this helps.

Best Regards,
Ray @ Raylar

Thanks for the replies, I was just wondering about longevity with the powdered metal rods and ring end gaps. Like I said I don't spend much time at WOT. I plan on replacing the entire exhaust system with an aftermarket system (aluminum manifolds, stainless risers) and a capts. call option anyways. I'm also installing a drive shower for the long haul.
Thanks again

I ran a 360ci SBC for two years and it was just a 2blt cast crank, PM rods, cast pistons. I had AFR 190 heads, Performer RPM, 1.5 RR, upgraded exhaust, Holley 750, 224 flat tappet cam. Ran that sucker hard for 360hrs with no problems of any kind. Alot of time at WOT 55-5600rpms. I tore it down to check it out after reserving it for a spare shortblock and it looked really good. Visible crosshatching, minor skirt wear, no bore polishing. It had very good compression and leakdown numbers.

Ray, Thanks for confirming that info. I knew Merc's shortblocks were the same as the ones GM sends out in cars. My Stock 350 260HP ran fine for close to 1000 hrs with those tight GM automotive clearances. LOL Also explains why ZZ502's and HP500's when torn down have the same parts and clearances.

Ryan00TJ:

Be careful here with some broad comparisons. All the Mercury Racing (not Mercruiser) engines are built from seperate parts in Fond Du Lac by Mercury Racing Technicians and I don't beleive they share much in common with any GM crate motors. Mercury Racing uses some really nice parts some of which are GM performance pieces like some blocks and crankshafts, but a lot are parts from Manley, JE, Edelbrock ( Mercury Proprietary aluminum head), Dart, World, Crane, Clevite, etc,etc. they do not produce any motors such as the HP500 carbed and efi or the HP525efi, and so on that start life as GM crate engines. These Mercury Racing engines engines are all basically prepared with a "blueprint spec" and are hand assembles with great machining and assembly care with a lot of the parts above. Thats why they cost more than Mercruiser engines, same parent company different products!
I also know that certain GM Performance crate engines are now using a few aftermarket suppliers in pistons, crankshafts, cams, etc. for some of their special offerings and the build quality on these engines as well as numerical machining control has improved greatly in recent years in these engines as well. But they are still to different animals and entities. The times they are a chang'in and even in the engine build business, so be careful of certain things you hear said by some in our sport who know "Just enough to be Dangerous!"

Best Regards,
Ray @ Raylar

Raylar, looked up that GM part number, says it is a 290 hp motor. My motor says 260hp, or is that rated at the prop? GMPP 350 is rated at 330 hp, that means I would only be adding 40hp for a grand more. The only thing I can see being differant are the heads are vortec small chamber heads. Or am I totally confused now?

chapp-sx:

Trying to make sure you don't get yourself in a box here. Your thread said you were upgrading an old 350, so I assumed (should not have done that) that your existing motor was an older model with the older style intake bolt pattern or EFI unit. The newer HO350-330 uses the newer vortec heads with a different bolt pattern on the intake manifold and it is not a marine manifold with brass in the water crossovers. If you plan to upgrade with a new crate motor including fuel system, carb or late model efi then the later vortec HO350-330hp motor will work fine with the changes I mentioned. You will most likely have to investigate the cam spec in terms of lobe centers and overlap to make sure the reversion enemy does not rear its head here.
There should be some guys here on OSO who have made this swap and can shed some more light here. You might wan't to post exactly the year and model of your mercruiser engine.

Best Regards,
Ray @ Raylar

I have used a few of the HO350-330hp motors #12486041 they work great and you can't build one cheaper, no reversion issues at all. The older style two piece rear main 350-290hp #1299529 has a stupid cam and and I have even seen a couple that didn't have enough retainer to valve seal clearance right from the factory and smashed the seals. If you want the old style package the Goodwrench 350-260hp is a better bet.

Sorry for any confusion Ray, I'm going to pull the 260hp and stick it under the bench. I was told the HO350-330 hp would be a good replacement for my application. I do have a good seasoned 4 bolt block under the bench also. My buddy has a cousin that owns an engine shop, so I can get the machining done for next to nothing, and looking through the Jegs catalog and online, it looks like I can build pretty much the same package for under 2k if I do it myself. I would just need to add anodes to the vortec intake. Realistically I would like to have about 350-375HP when I'm done, and my original thread was just asking if anything special went into a low-medium perfomance marine motor (under 400Hp), sorry should have clarified that. I'm just trying to hot rod the family cruiser, not build a fire breathing wave skimmer LOL. Thanks for the education, and all the replies. Anything else I forgot please let me know

Thanks
Chapp-sx