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  #46 (permalink)  
Old 10-06-2006, 01:39 AM
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I'm glad to see someone brought up that some marine motors are reverse rotation.

Ford does use a different casting for marine motors. The 351W in my '94 Lightning is a marine motor with a marine part number on it. All the early (93-95) Lightnings had these marine motors. Marine crank, marine cam, better pistons, etc. These blocks (and internals) will reliably handle 500hp even though they shipped with only 260.

I'd love to find an wrecked boat around here the the 427 FE in it that I could steal for my Mercury!

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  #47 (permalink)  
Old 10-06-2006, 02:02 AM
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Funny that this old thread came up again...

I scanned through and got the feel of the thread, but didn't have time to read all four pages, so if I repeat something please forgive me. Here is what I've recently learned about marine stuff.

I had always heard several things about marine blocks. There are all kinds of rumors about 4-bolt mains, extra silicon or nickel in the blocks, special reinforcing, the works. It made sense since automotive engines spend 90% of the time at 20% throttle and boat engines spend 90% of the time at 90% throttle.

Well, after three months of research into building my first marine small block, (I'm one of those who needs to know why ) I am here to tell you that for the most part... and here it comes... drumroll please.... '

wait for it.....

A GM marine small block is fitted with brass freeze plugs. Period. Anticlimactic, huh?

I really dove into it. I looked at the operational theories of marine use and logically reasoned out several things.

Marine blocks use standard oil pumps. I thought for sure they would use high volume or high pressure pumps for the extra stress. High pressure isn't needed since we're talking about a 5000-rpm engine. As long as you have 10 psi per 1000 RPM, its fine. High volume can actually be trouble. Since they spend so much time at 4000+ rpm a high volume pump can send oil OUT faster than it drains back.

Marine blocks up to 300 hp use cast cranks, cast rods, and cast pistons, all spinning on 2-bolt mains. I thought for sure they were all built with forged rotating assemblies, but the stiffer, more brittle cast lower end is actually preferred below 5000 rpm. I was really caught off-guard with the cast piston choice, but it makes sense: Forged pistons tend to expand and contract more than cast requiring greater piston-to-wall clearance. In an automotive application the pistons and block reach a mostly steady temp meaning you can predict how they'll perform once the engine is at operating temperature. In the case of marine engines where the thermostat temps are lower (usually 145-160 max) the block stays cooler while the piston is CREAMED with constant wide open throttle combustion. The block thinks its going for a sunday drive while the pistons are saying "holy s#!t, what the fck!." The thermal stability of the cast or hypereutectic piston is preferred for this reason. Since the target RPM of most boat engines is 5500 or less and the HP is usually under 400, cast or hypereutectic is more than adequate.

Sorry if I repeated stuff, but I wanted to know the when where and why of marine small blocks so I ordered two books and sapped info from four boat tech forums before I dove into my own build. Interesting stuff to say the least.
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  #48 (permalink)  
Old 11-01-2006, 12:50 PM
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marine block

I also got here late, and may repeat someone. When i was with E.H.Boat, and Pacemaker our offshore marine engines had heat exchanges, the salt water did not contact the block. The exhaust manifolds were also water cooled. but the blocks them selves were not different than any other block.
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  #49 (permalink)  
Old 11-01-2006, 04:01 PM
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I, too, am late. I can't vouch for GM engines, but I doubt that they are different than the Fords. Ford blocks are not any better and often times are less sturdy than the car block. The comment from the one poster regarding finding a marine 427 for his Mercury shows a lack of info regarding these. MOST Ford 427 Marine blocks do not have the side-oiler feature drilled and the castings are not any better. Marine engines are usually run at steady state speeds and don't encounter the kind of thrashing and rpm fluctuations as a car engine and so they aren't as developed as their sister HI-PO car engines. Many a Cobra owner has dropped a wad of money on a Marine 427 and found that they paid more for it than they could have built a Genesis engine , fresh and new. They do have torque type cams usually and the first 5.0 performance engines in the 80s used a marine cam initially and a 5.0 GT performance cam was generated later. If you can get one at a decent price it would probably make a good medium performance street engine, but they are not worth anything extra. Also be aware that ones used in tandem have one engine that turns backward, so make sure it isn't on that side.
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Old 05-30-2013, 04:03 AM
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The 3.0 GM engine used in boats has been around a long time, it is a very rugged, dependable little engine. The Mercruiser and Lesney Foundry have a thin casting in it. I have been using both but couple of month ago it got damaged then I purchase a used engine from an online website ***************** and it is running smoothly.

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  #51 (permalink)  
Old 05-30-2013, 06:58 AM
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mercruiser gm engines from the alpha1 gen1 series and later, have blocks with a higher nickel content and brass freeze plugs as well as stainless head gasket and to resist corrosion in the block. and also merc uses nodular iron cranks to save weight for vibration resistance and add durability against high torque loads, weather or not you need the nodular crank or not its in there.. im suprised that this entire thread devoted to the comparison and nobody has a definitive answer. look up the block number from a mercruiser block either 350 or 305 cubic inch displacement and you get a marine only block. pretty cut and dried. sure marine vs auto are interchangeable in measurements ...however one is definately better than the other. marine engines are better. automotie engines are put together using whatever hired help that can work on the line and mercruiser engines are built by skilled engine builders. yall can keep throwin brass freeze plugs in a auto block for your failed winterization fix but dont kid yourseves here. marine block numbers from late 80's on, dont cross reference to any automotive app ever. period.
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Old 05-31-2013, 10:11 AM
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This thread is 7 years old, but a lot has changed on teh scene. No longer does GM supply Mercruiser with Big Block engines. Mercury has developed its own Big Block engine with 32 valves running dual overhead cams with twin turbochargers which produces 1350hp from 9 liters or 552 cubic inches using a 4.57" bore/4.21" stroke and a 7.8:1 compression ratio. All this power using 91 octane (R+M/2) unleaded fuels.

Then they introduced the Mercury 1650, wgich makes 1650 hp from the same 32 valve 552 cid TT engine, but uses larger turbos and teh same 91 octane fuel requirement
For the 1650 engine
.*This product is highly specialized and produced in limited quantities for sale, without warranty, to qualified powerboat racing professionals

The 1350 engine have a 1 year limited warranty for recreational use, there is no warranty on the 1650hp engine.

All this new pawer required a new drive unit, so the M8 dry sump drive was invented. A 1350 engine and M8 drive can be had for $200,000 for the pair.

For SBC engines, Merc used the GM blocks for years and years. The blocks themselves at least from 1996 are the same blocks that saw usage in the 1996-2002 Vortec 305/350 trucks/vans and SUV's. These engines were a GEN 1E series, or Generation 1-E for Enhanced. MAny Merc 305, 350's were direct from GM with teh Vortec heads and this MPFI marine intake which Merc called teh IAFM(Integrated Air and Fuel Manifold.

IAMF on the left and CSFI 1996-2002 Vortec 305/350 truck/van/SUV intake on right(I have an IAMF installed on 1 of my Vortec 350 equipped trucks in order to get conventional fuel injectors which can be retrofitted as the need arises.

While higher outout SBC's(340+hp) got many different versions of this tunnel ram intake manifold. The Scorpion series used these intakes.

The lower tunnel rams were the same, with differnt upper plenums installed. Here is a progressive throttle body with dual throttle blades installed in a vehicle. There were lower tunnel rams for both 1996+ Vortec heads which use 8 vertical intake bolts, and the older GEn 1 heads with 12 intake bolts at an angle.

400hp Scorpion with the same vortec headed tunnel ram with the Scorpion upper plenum with its throttlebody at the upper right of the engine.

Pic showing the differnce in ports between the GEN 1 and GEN 1-E Vortec heads.

IIRC I was told here on these forums that the marine engines use differnt main bearings than the automotive engines

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  #53 (permalink)  
Old 05-31-2013, 10:51 AM
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The 1350HP Big Block is a Mercury Quicksilver racing engine. It is not a regular production engine.. Mercruiser still runs GM Big blocks except they are cast at Mercury Marine casting plants.. They have great engine designers, they also designed and built the ZR1 engine for the 1990-1995 Corvette ZR1, also in the late 70's they built the 3.7L 4cyl which sucked for a boat but for a vehicle ( retrofitted ), they are great. Iron headded aluminum block 4cyl running Ford 460 internals to make 165-190HP at fairly low RPM's.

That said, the myth is that Mercruiser got the top 10% of the blocks from GM and built them with Nodular cranks and such, but that's not true. They just bought what was available and marinized it. Blocks and engines that they cast themselves are top tier engines tho.
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  #54 (permalink)  
Old 05-31-2013, 12:34 PM
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The LT5 was designed by the then GM division, Lotus Engineering. Mercury built the engine using some of their own castings and some outside sourced pieces.
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  #55 (permalink)  
Old 05-31-2013, 05:01 PM
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Originally Posted by Jzarczyn View Post
Or you could just use a rad. Using water that cold to cool your motor will cause overcooling and a consiquent loss of fuel economy.
We run a 165 thermostat that allows water to run through the water cooled exhaust manifolds to exit out the exhaust. When the thermostat opens, heated water runs through the engine from low to high, again exiting through the exhaust. Very efficient. Keeps operating temp in the 170- 180 range on exit.
We also can run restrictors where the water exits, a little less efficient, but foolproof. No thermostat to fail or hang open from seagrass.
Manifolds and aluminium intakes need to be flushed each time and inspected on a regular basis. Salt water eats them up. Never heard of any coating inside on marine blocks.
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  #56 (permalink)  
Old 06-06-2013, 07:46 AM
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Originally Posted by lmsport View Post
The LT5 was designed by the then GM division, Lotus Engineering. Mercury built the engine using some of their own castings and some outside sourced pieces.
Ding ding ding! The reason Mercruiser was chosen was because they had the most experience with casting aluminum. The produced the engines fromthe late 80's til 1993.

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