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Old 07-31-2007, 01:44 AM
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Default marine engines versus car engines


Is there really a such a big difference between marine and automotive V-8s? The answer is a resounding yes. In fact the differences between the two breeds are so striking, one ought never place an automotive engine on stringers where a marine engine used to lay.

The biggest difference is the cylinder block. Marine engines are based on heavier-duty truck blocks, with four-bolt main support of the crankshaft instead of just two. Keep in mind a car only uses about 15 of its one or 200 horsepower to sustain a speed of 55 mph. Conversely, a boat is always under load. Its marine cycle can be compared to hitching a 10,000 pound boat and trailer on the bumper of a car and trying to climb the Rocky Mountains at 80 mph.

Besides duty cycle there are other important differences. A marine engine’s core plugs are corrosion resistant bronze. The camshaft is ground to different specifications, most often to maximize low end torque. Valve overlap (the time when both intake and exhaust valve are open) is shortened to minimize the chance of water being sucked out of the exhaust and into the combustion chamber. Gaskets are premium quality for better sealing.

Most important of all are the starter, alternator and distributor. All three components are fitted with special screens that quench internal sparks that might otherwise vent into the atmosphere and light-off gasoline fumes present in the engine compartment. For the same reason, a marine carburetor bowl vents overflow to its throat, instead of to the atmosphere. The bottom line, an automotive engine is totally inappropriate for a boat. Its torque curve won’t meet the needs of a boat, its light-duty components won’t long survive the rigors of marine usage, and you risk blowing yourself out of the water. You decide.


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Old 07-31-2007, 02:37 AM
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Default Re: marine engines versus car engines

I run a Subaru car engine in my mudboat... high RPM's at all times. If only Subaru would get into the marine business... I'd be the first in line to give it a shot.

I understand this is not what you were getting at... a mudboat is a totally different animal. But as bulletproof as these Subaru car engines are... I'd love to see how they'd do with an outboard.
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Old 07-31-2007, 08:49 AM
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Default Re: marine engines versus car engines

So what you're saying is; they have a truck/rv cam and a set of brass freeze plugs. the starter/ alternator/carb are bolt ons. and the 4 bolt main thing only applies to GM's, not Fords. I call BS on block differences, they are the same.
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Old 07-31-2007, 09:00 AM
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Default Re: marine engines versus car engines

If you are running a full fresh water cooling system the gaskets and plugs don't even have to be changed. Most older marine motors were truck motors; but the crop available today are not. Look at the 8.1's sucking in seawater because of the valve overlap. The 6.0 is the same motor that is in my Hummer. I guess my H2 is a truck.
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Old 07-31-2007, 09:03 AM
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Default Re: marine engines versus car engines

I strongly disagree. The blocks, cranks, rods, pistons, valve train components are the same. Camshaft profiles are actually more agressive, with more duration and more overlap, with tighter lobe centers. That's why marine engines idle higher..lumpy camshaft. All the rest of the items are bolt-ons, and are indeed marine items, mostly being "sparkproof".

Don't perpetuate this "marine" myth..GM simply doesn't build special heavy duty engines strictly for the marine market.
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Old 07-31-2007, 09:10 AM
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Default Re: marine engines versus car engines

not to mention that most are still only 2 bolt mains
the vortec is when all the water ingestion started due to camshaft overlap
and the best is they are made in mexico where the tin content is lower and the blocks not as sturdy as the older ones

you should look up some old boats with the 427 side oiler fords or 427 cross ram chevy or even older the 354 hemi that had a gear(trans) bolt onto the front Gray marine i think made that one or should say "marinized" it
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Old 07-31-2007, 01:36 PM
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Default Re: marine engines versus car engines

hate to tell ya but i had a 19' marlin skiboat ran 54mph withthe stock eng
pulled an eng out of a 87 blazer bolted right in 1st run 55mph ??

sold it the next year and it's still running 5 years now

brass freeze plugs and in some cases the cam
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Old 07-31-2007, 01:40 PM
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Default Re: marine engines versus car engines

I think Timebandit couldn't sleep and thought he would try and stir up some shi.... er, I mean start a meaningful discussion on auto vs marine engines
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Old 07-31-2007, 01:50 PM
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Default RE: marine engines versus car engines

Quote:
The answer is a resounding yes. In fact the differences between the two breeds are so striking, one ought never place an automotive engine on stringers where a marine engine used to lay.
Sorry but that's a bunch of crap...the differences are basically bolt ons and in some cases SS exhaust valves....do you really thing GM / FORD / etc are going to build completely different engines just for a few boats?

If your statement is true, then why did 100% of the PCM marine components that I purchased bolt right on a truck block, and has been in service for over 6 years. "0" problems.

The Differences are certainly no big deal for the average mechanic:

>Brass freeze plugs
>SS exhaust valves (optional)
>Aggressive high lift / short duration cam
>Marine carb / Alt / Starter
>Marine ignition (some debate here)
>Brand "X" marine components, i.e manifolds, raw water pump, etc.
>SS head gaskets (if raw water cooled)

Basically that's about it, and I would not call this list "striking"

Diesels vary....some OEM's used quite a bit different stuff and some used the same stuff EVERYWHERE....as did Detroit (one BOM fits all)
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Old 07-31-2007, 01:55 PM
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Default Re: marine engines versus car engines

HEEHEEHEE lets throw some gasoline on this here fire. http://www.atkinsrotarymarine.com/ Put a Supercharged Rotary Engine in your boat!
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Old 07-31-2007, 02:21 PM
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Default RE: marine engines versus car engines

[quote Timebandit]
Is there really a such a big difference between marine and automotive V-8s? The answer is a resounding yes. In fact the differences between the two breeds are so striking, one ought never place an automotive engine on stringers where a marine engine used to lay. The biggest difference is the cylinder block. Marine engines are based on heavier-duty truck blocks, with four-bolt main support of the crankshaft instead of just two. Keep in mind a car only uses about 15 of its one or 200 horsepower to sustain a speed of 55 mph. Conversely, a boat is always under load. Its marine cycle can be compared to hitching a 10,000 pound boat and trailer on the bumper of a car and trying to climb the Rocky Mountains at 80 mph. Besides duty cycle there are other important differences. A marine engine’s core plugs are corrosion resistant bronze. The camshaft is ground to different specifications, most often to maximize low end torque. Valve overlap (the time when both intake and exhaust valve are open) is shortened to minimize the chance of water being sucked out of the exhaust and into the combustion chamber. Gaskets are premium quality for better sealing. Most important of all are the starter, alternator and distributor. All three components are fitted with special screens that quench internal sparks that might otherwise vent into the atmosphere and light-off gasoline fumes present in the engine compartment. For the same reason, a marine carburetor bowl vents overflow to its throat, instead of to the atmosphere. The bottom line, an automotive engine is totally inappropriate for a boat. Its torque curve won’t meet the needs of a boat, its light-duty components won’t long survive the rigors of marine usage, and you risk blowing yourself out of the water. You decide. [/quote]

And your point is?
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Old 07-31-2007, 02:51 PM
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Default Re: marine engines versus car engines

I'd like to see some engines like the Ford v10, and 4.6 marinized as well as the aluminum block BMW 4.4 and the Northstar. I just don't think there's that much r&d on newer motors since the old iron block/pushrod engines are so cheap and plentiful. Some day though, we'll be seeing all alloy engines with overhead camshafts, crank triggered ignition, fuel injection and turbocharging replacing the old dinosaurs. Be nice to have a 400 pound engine putting out 350 HP instead of a 1200 pound big block.
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Old 07-31-2007, 03:06 PM
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Default Re: marine engines versus car engines

ever took a good look at a honda out board i-4 or v-6 ?
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Old 07-31-2007, 03:34 PM
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Default Re: marine engines versus car engines

There is a difference in cams and that's about it. And that difference is in the lobe center. Marine cams have less overlap (wider lobe center #'s), since their exhaust isn't delivering much in the way of scavenging, or pulse enhancement.
The other bolt on stuff can be modified to work or be compliant.

The distributors are of lesser quality. Won't see an HEI on a marine app.

But now it's distributorless and that's a great improvement.

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Old 07-31-2007, 05:29 PM
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Default Re: marine engines versus car engines

Not all marine blocks are 4 bolt mains. Good example was the 305 chevy block.
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Old 07-31-2007, 06:00 PM
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Default Re: marine engines versus car engines

Taker a look at Chesapeake Bay watermen's boats. Many are powered with auto engines with dry stack exhausts. Olds 455s are the favorites. Just need a raw water pump for cooling. Engine goes bad, go to the salvage yard and pick up another. Realize this is not in the vein of the original post, but going with the response my computer repairman gives to every question: "it depends".
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Old 07-31-2007, 06:32 PM
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Default Re: marine engines versus car engines

timebandit, your diatribe looks familiar. You didn't perchance cut and paste from somewhere?
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Old 07-31-2007, 06:45 PM
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Default Re: marine engines versus car engines

That brings a question.

Why can I buy a car with the same engine, 4 wheels, seats, AC, radios, and all that crap for a cheaper price than a stupid outboard with the same HP, and in some cases (honda) basically the same V6.

If you say it's because the marine market is small, well maybe, but it's the SAME ENGINE, produced in the hundred of thousands, with differences of course.

But still we are talking a simple engine, with a transmission that only has Forward and reverse, costing more than a whole car (a lot more metal involved), multi-speed transmissions, Electronics up the wazoo etc...

It's nuts.







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Old 07-31-2007, 10:13 PM
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Default Re: marine engines versus car engines

Quote:
catastrophe - 7/31/2007 5:45 PM

That brings a question.

Why can I buy a car with the same engine, 4 wheels, seats, AC, radios, and all that crap for a cheaper price than a stupid outboard with the same HP, and in some cases (honda) basically the same V6.

If you say it's because the marine market is small, well maybe, but it's the SAME ENGINE, produced in the hundred of thousands, with differences of course.

But still we are talking a simple engine, with a transmission that only has Forward and reverse, costing more than a whole car (a lot more metal involved), multi-speed transmissions, Electronics up the wazoo etc...

It's nuts.
Not sure how you figure the cars cost less than the outboards.
Honda BF150 is about $13k installed.
Honda Accord with the same motor costs about $25k. The CRV and Element share the same motor and run around $20k +.

Honda Odyssey and Pilot are $26-40k. I doubt a BF225 with the same V-6 costs anywhere near that much.

Honda Civic: $17k+
Honda BF90: $9-10k
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Old 07-31-2007, 10:31 PM
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Default Re: marine engines versus car engines

A Honda BF225 is essentially a Honda Odyssey engine stood on end, with a lower unit under it and a cowl. They list at about 18K. A base Honda Odyssey (The version that won't tow 10,000 pounds) costs about 24K. For the 6K difference, you get a transmission, differential, four tires and wheels, air conditioning, and a body.

I love Hondas and I've had 225's and a couple Odysseys. There's a lot more profit in a BF225 than in a Van.

And, more importantly, I also call BS on the block issue. The freeze plugs are brass, not bronze and the blocks are the same. Stainless valves may be added in high dollar engines, but your basic Mercruiser 350 shares most of its parts, from valve covers to pan with the good old crate 350 every dealer stocks.
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