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What's the difference between a marine and a normal motor?

C

cass

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This might sound stupid, but I can't get a straight answer on this. What is the difference between a marine engine and a normal engine? I have a 1991 Mercruiser 305, with a normal alpha 1 OD. Is this a reverse rotation engine? Can I use normal chevy rebuild hardware on this (ie pistons, rings, cam, etc)? Please help with the confusion. Thanks
 
In the sense of how the SBC comes from General Motors, you will normally find a few of the following, minus electrical components:

  • Compression ratio suitable for a marine cruiser type engine.
  • Special head gaskets that will hold up against the corrosive action that can result from sea/lake/river water cooling.
  • Bronze/brass casting plugs... see above.
  • Marine Engine Circ Pump will have a special ceramic shaft seal.
  • A marine profile camshaft for multiple reasons.... intake/exh over-lap being one.
  • Dual plane intake manifold on carbureted engines.
That is basically what you will find from GM on the SBC marine. If you were to get into a more true marine version, several other items change as well and the cost can be much greater.
If planing to use an automotive engine, you will have issues with head gaskets and casting core plugs if not installing a Closed Cooling system....., and you may have cam profile issues.

Again, does not include ignition, starter, alternator, fuel delivery, of which are all quite different for marine.
 
I just realized that I did not mention rotation.
Standard rotation for marine is LH, and is the same rotation for auto.
This is viewed from the flywheel side, and would be considered a Counter-clockwise rotation.

A Counter Rotation or RH marine engine, when viewed from the flywheel side, would turn Clockwise..... and is normally the Stbd engine!

Again, when viewed from the flywheel side.
 
That makes sense about the counter rotation. Thank you for clearing that up. I am rebuilding the 305 in my boat, so I already have all of the components, I am just rebuilding the motor. Will a normal rebuild kit for a chevy 305 work? I already have the crankshaft, heads, mainifold and block. I just need gaskets, pistons a cam and rings. Do you think this will work?
 
I will add my little bit in that the Camshaft has to be Marine Specific, to gain the optimum performance and fuel economy, as the engine will be cruising at one speed, like 4,000 RPM, constantly for hours on end, and a WOT of up to 5,000 RPM. The Road engine will virtually never see for more than a short time, like during gear shifting.

The Marine Engine will only experience idling speeds whilst proceeding through Moorings and the like, and to the Launching Ramp or Pier.

The type of Pistons you should use will depend on what quality of fuel you will be using, as it is useless putting in too high a compression pistons that can cause combustion problems later on.

If you are using a Closed Cooling System, you can use standard Automotive Gaskets, Welsh Plugs, Water Pump and the like, but I never use Steel Welsh Plugs, and only Brass, or Stainless Steel these days.

Any other cooling system, you need the correct Marine parts to combat the effects of Environmental Corrosion.

Bruce.
 
Bruce, I have to restrain myself when it comes to the topic of dished pistons vs a q/e piston to use in a SBC Marine engine!
Another story for another day, eh? :)
 
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So merc makes the motor or does gm make the motor on the same line as auto motors ?

If you picked the second option you would be correct.

So the vortek motor in that van you see going down the road has a cam that is so close to a marine one that what? Is the same one in your boat ? Yep.

Has anyone seen the casting plugs in the gm van going down the road. Yep.
Same one in the boat motor, and the head gaskets, yep the same ones in the boat motor.

What is different ? The starter, alternator, dist. all marine SAE J1171 Marine marked on them.

So if you need a motor call up gm and have a new crate motor deliverd and save half the price of a " Marine " one if your doing the work yourself.

See merc won't warranty the motor if you do the work yourself. So the bull about warranty from the marine motor people is just that bull.

Rebuilt different story, but then again you gonna trust a rebuilder?
 
Chief, are you suggesting that GM is installing the same head gasket in their marine line as they did in the auto line of SBC engines?

I believe that this format engine is all but dead in the new car/truck world....., but is continued as a crate type replacement engine... both auto and marine, correct?
 
They don't ? Ok put a marine one on. Whats the marine one gonna be made of? See if the one you took off is any different ?

I fell into that one when we did my friends motor. Again depends on what year motor if it's a true vortek then it will have the same gasket.
 
Did anyone mention cast iron rings? Gotta have cast iron rings. Not that girly chrome Molly stuff..(assuming salt water is involved)

Cheif.. dont start Richardo on those disshy quenched pistons.. we could go up to 160 posts:D

Richardo.. wheres my coke?

Mark
 
Marine head gaskets are stainless steel. Some car head gaskets may also be SS, but that's coincidence. Only a big deal if the engine is raw water cooled. Same goes for the freeze plugs... if raw water cooled, they need to be corrosion resistant (usually brass or bronze).
 
Mark, here's your Coke.
Ah....., I was thirsty.... sorry!
images


And there are no "disshy" quenched pistons.... that's the problem! :D

One other thought here......., if building a SBC marine that will be Closed System cooled, you can use a "high grade" auto head gasket set and you can use the auto version Circ Pump.
(One issue may be the bi-directional Circ Pump for REV rotation.)


(when I grabbed that coke bottle image, I found something strange.... do a Google "Image" search for "coke bottle".... Hint... X-ray view! Yuck!)
 
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Mark, actually there is a SBC "disshy" type Q/E piston found in a Low Compression Q/E or a Reverse Dome style. These are a good choice, IMO.
So in a sense, you're right!
(I just have an issue with that "dish" word! :rolleyes: )
images
 
err sorry mate, didnt mean to take you there, Im thinkin of all those emergency room medicle stoies ive heard..they are makin my skin crawl..
I Promise, wont mention the C word (or the dish) again. Mark.
 
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this is fro, mercury marine training

this is only the internals not external electrical!
 

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Dem " dished pistons " how are they for the long term? Don't get me wrong i honestly would like to know ?

They gonna last 30-40 years ? Or are they for like 2-3 years ?

Seems they would better suited for a track motor .

Maybe 400-500 hp motor, super high compression.

Marine motor do you really want or need that high compression, or 140-170 psi ?

I say once again between the 5.0-5.7 same money you can build a 5.7 more torque and 300 hp and have the same weight.
 
This can easily become one of those heated topics.... and I wish to avoid that.
These are my thoughts only, and are not intended to start an argument here.:)
It's always a good discussion though!

Chief, just to clarify......, the full dished pistons are what GM is commonly using in these SBC marine engines to render the correct C/R. If we have a Mercruiser SBC, this is very likely similar to what you'd find in this engine.
These are inexpensive to produce! They work well, but do not offer a Q/E (quench effect)!
images


It's the Low Compression/Quench Effect piston (or "Reverse Dome") that I am speaking of. (yes, there is still a dished area in this design.... but not under the wedge!)
The advantage is the quench area that comes up under the "wedge" of the cylinder head.
These are more expensive to produce!
images

Chief, the above piston (when custom ordered for the application) maintains the same C/R that the full dished piston does. So we have no issues in this area!


Regarding the OEM Mercruiser technical information:

1) I believe that the oil pans used by M/C are nothing more than a fairly standard GM oil pan as we would likely see in auto/truck use. A more true marine oil pan may be found with PleasureCraft or one of the big boat marine engine manufacturers such as an aluminum high volume pan!
2) for years their marine engines used the two bolt mains. Yes, I'd prefer four bolt mains when I build or buy one today.
3) Hardened valve seats were not necessarily a result of a marine environment requirement.
4) and the comment about pistons that improve detonation resistance I would take issue with!
For years the GM marine engines that M/C has used, have been fitted with the full dished pistons to accommodate 64 cc combustion chambers. This is NOT a piston that is good at resisting detonation, IMO.
Why is this piston used?
I would assume Cost and Cost only! It can't be anything else!
5) Roller cam followers.... no brainer! Far better, and most all are rollers these days.

Pretty sure I've mentioned this before, but if any of you have access to Dennis Moore's "Small Block Chevy Marine Performance", you will find a very nice explanation from Dennis on the use of a Q/E piston, over that of the full dished piston.
All of this info is regarding detonation control in the SBC that uses a "wedge" shape as part of the cylinder head combustion chamber design.
It's the wedge and the full dished piston that are the issue!

My point being, for a few more dollars you can build a more true SBC Marine engine. Compression ratio remains the same if a correct piston selection is made.

Thoughts???
.
 
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Compression remains the same ? No heated pizzing match i love these discussions.

I can see these pistons are alot like airplane motor pistons, dished like the pic.
 
chiefalen said:
  1. Compression remains the same ?
  2. No heated pizzing match i love these discussions.
  3. I can see these pistons are alot like airplane motor pistons, dished like the pic.
Click to expand...

1. Yes.... if the correct L/C Q/E (or Rev Dome) piston is selected..... Basically no different than ordering many other piston for a custom application..... but these do cost more! Not enough to break the bank, however!

2. Me too! Can you tell? :D

3. That I would not know!

Chief, not that you asked, but when we fight detonation with a correct piston/chamber configuration, we no longer need to hold back ignition TA.
Now we can throw a little more TA at the engine and pull that remaining horse power from it! And THAT is where much of the gain is!:)

BTW, the standard ole 5.7L flat top pistons (w/ single valve reliefs) when used with the larger chamber heads, can accomplish basically the same thing.
It's the small chamber heads (64cc), and added stroke of a 383 that makes this piston a poor choice, IMO.

.
 
87concord said:
does anybody know the size of the combustion chamber on a SBC vortec head for a 350 cu in engine??
Click to expand...
Double check your casting numbers against these....... they do show several casting numbers.
http://www.vehiclecarhistoryreports.com/chevrolet_engine_numbers.html

10239906...........96-up...350.........."Vortec 5700", "L31", 170cc intake port, 1.94"/1.5" valves , 64cc chamber

There are calling these "Ports" rather than "chambers"....... probably a typo!

25534351C..........04-up................Gen.I Bowtie, cast iron Vortec head, 175/65cc ports, 2.00/1.55 valves, "small port head"

25534371C..........04-up................Gen.I Bowtie, cast iron Vortec head, 206/77cc ports, 2.00/1.55 valves, "large port head"
 
Question, Ive always been told that a mercury marine engine also differs due to the fact that a marine block has different casting material ,that when salt does start to break down the casting it turns to a lighter/powder shale that exits the engine with the cooling water, and a " car" engine turns to shale which In turn blocks the water ways,... Is this correct?
 
Never heard that, but I once worked on an early Mercruiser (327 Chevrolet) that had eitrher a Coper or Brass Plated Rochester Carby, with Stainless Steel shafts and Platers, and a complete Copper Sump.

Bruce.
 
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