Auto vs. Marine motor assemblies?

Silly Seville · Aug 16, 2011

I know that this topic has been visited in a variety of ways, but I hope to generate more specific answers to a troubling question.
Other than the obvious external parts, like starter, alternator, distributor cap, power steering pump and exhaust system...what are the key cost differences associated with the engineering and or production of a marinized engine versus a standard truck engine? Is it perhaps industrial grade bearings, rods, cams, pistons and rings? Stronger valve springs? More precise porting of the heads? Gold filled lifters and diamond encrusted water jackets? I'm trying to understand why a marine small block Chevy is so much more expensive than its automotive equivalent. Could it be simple supply and demand, or is the issue more academic than that? I look forward to your answers, both serious and silly.

HT32BSX115 · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

Howdy,

Think supply & demand.

Automotive long blocks are made in the thousands. Marine long blocks are made (with brass core plugs, different camshafts, maybe different head gaskets( for salt water) stainless steel valves, etc.

Anything that makes them different (even if the different parts only cost a little more) and sold in smaller numbers will always cost more over all....

regards,

Rick

floridaboater1 · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

Think of it this way when you hit the throttle the front of the boat lifts up its kinka like driving a truck with a trailer uphill all the time. Your engine would not last that long. The marine engine is built with tougher parts and is made to do this. If i were you i would not put a automotive engine in a boat. Sure would suck to put a new engine in and do it again next year.

singlesupra · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

Pretty sure the guy is looking for FACTS, not your oppinions or thoughts on why.
Tougher parts huh? Is that why the recline is so much lower? And your engine. being raised verticly is laughable at best. One would assume you are revering to the oil being in the rear of the pan. Problem there that neither of us knows the answerto is which puts the oil back further/faster, raising the bow or the higher gforces. exerted forcing it back there. My guess would be the later, same when turning the steering wheel.

Since were giving our oppinions, my guess would be supply and demand, lots of. missinformatiin and the fact that I beleave 95% of all boat mechanics to be complete crackheads or atleast the bottom of the barrel for some reason

emilsr · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

It's one of those "your mileage may vary" sort of things. Some are a little different, some are a lot different.

For example, we've got a Mercruiser 496magHO in our boat. It was based on GM's 8100 Vortech truck engine but has different heads, a different cam, different intake, computer.....pretty much only the block and the rotating assembly are common to both marine and automotive.

I'm told that the old 7.4mpi was very similar to the engine Chevy used in their 454SS pickups. Just depends on the model and year how big the differences are.

StevNimrod · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

There's a lot of misinformation and fear when it comes to this stuff (i.e., if you don't get a "marine" engine, you will lose your hair, your wife, and a baby kitten will die).

As to the physical differences, it depends on the engine. Most differences are very slight. For the rest of the stuff, there are identifiable casting numbers that separate fact from myth (especially when it comes to forged crankshafts, thicker blocks, and a host of other things that are easily and usually disproved).

As far as price difference - when you are buying an OEM marine engine you are simply paying for a few different parts and one more middle-man. I believe that the best way, hands down, to get a precisely put together "marine" engine is to deal with a local reputable machine shop.

Bondo · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

Other than the obvious external parts, like starter, alternator, distributor cap, power steering pump and exhaust system...what are the key cost differences associated with the engineering and or production of a marinized engine versus a standard truck engine? Is it perhaps industrial grade bearings, rods, cams, pistons and rings? Stronger valve springs? More precise porting of the heads? Gold filled lifters and diamond encrusted water jackets?

ahhh Nope,... None of that stuff... Power steerin' pump ain't special either...

The rest of yer question is much to Vague, as production Mercruiser 5.7l motors aren't the same as a SBC comin' outa the Mecrury Racing Division...
The standard productions motors are darn near exact copies of the pickup truck motors...

Rick hit it pretty good with Supply, 'n Demand, then throw in that is the Marine niche market...

Ya gotta kinda be a Motorhead to get into the specifics of alotta the differences....
SBCs can be built into Many different motors with Many different tweeks...

StevNimrod · Aug 16, 2011

Re: Auto vs. Marine motor assemblies?

Bond-o said:
the Marine niche market...

That pretty much sums up the economics of it. Niche market = price discrimination (usually).

Think of it this way - if you could sell 10 engines and profit 50,000 (arbitrary numbers) or sell 100 engines (by lowering your price point) and make the same profit, which would you do? I can think of five reasons off the top of my head to just sell ten.

Volphin · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

Well, I have dug into about 3 different "marine" engines and they are the same as what I found under the hoods for 20 years working on cars for a living. They might have brass casting plugs, but the bottom line is that they are just tweaked for torque output through different cam profiles. Raw water stats are still 140 degrees (very cool) compared with auto stats, 195-210.

Another poster mentioned his HO. To make an HO, you go with a different cam grind, and port the heads (ever so slightly if it is from the OEM). If it is computer controlled, it may have a more aggressive timing/fuel curve.

I'll tell you guys what though... next time you buy a new boat and the dealer wants 30K for a 454 HO, message me. I'll build you a custom powerplant with the same warranty, more torque, more HP and better parts.

Seriously people. Fuel injection was even late to the game for marine. If anything, these engines are WAY behind the times.

V

Silly Seville · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

Hmm, it appears as though a post or two may have been deleted early in the thread..? Well, here is the reason for my questions. I am in a position to replace my 350/260 with either a donor truck motor for $500, or as a (do it right) alternative, a $1,600 marine rebuild. This vessel sits at mooring 7 months a year and the motor only runs at idle speed when I take her out for some languid exercise in the harbor. Given the gentle nature of use, is it reasonable to invest the additional cash for new internals, and some peace of mind; or shall I pocket the difference and take my chances, and lumps...if any? Further opinions appreciated!

emilsr · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

Check your local library, book store or Amazon for a book by Dennis Moore entitled "Small Block Chevy Marine Performance". This guy goes into quite a bit of detail as to the differences in marine vs auto.....would be worth your time/money to read if you're repowering.

If I remember right (and I'm old so I probably don't) the 260hp Mercruiser was basically a "stock" 350 with a different cam; nothing particularly "marine" about it ('cept for the brass freeze plugs), just was different than the automotive version in that particular combination of parts. Shouldn't be too difficult to replicate that engine with mostly (if not all) automotive parts.

flashback · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

just from personal experience. Mine is a 79CC re powered with a 350 truck engine 5 years ago and all I can say is it has been a good one..only problem I have had was a rocker stud pulled loose. I think that could happen with any of them unless the studs are pinned...at present I am sorting out a raw water pump, but that's another story.........

Silly Seville · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

emilsr said:
book by Dennis Moore entitled "Small Block Chevy Marine Performance".

Hey, thanks for that info! I will head out today to get a copy. I have all winter to consider my options for another motor and install, so I'm looking for the best deal possible...with the least amount of headache. I have been reading every thread or post that I can find about Rapid-O Marine engines. Wow, talk about mixed results! Most positives simply say, "Engine runs fine-no problems", while the negatives go into great detail about how angry and dissatisfied they are with the treatment or care they received as customers. Having said that, does anyone who has fresh perspective (meaning recent Rapid-O re-power) want to chime in here?

Flysfloatsor · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

When it comes to SBC, there isnt much difference. Brass core plugs, marine head gaskets (who knows if they even do that) and different cam.

kilowatts · Aug 17, 2011

Re: Auto vs. Marine motor assemblies?

Hi Guys:

I don't feel qualified to give any kind of definitive answer but....

My brother-in-law owns 2 Detroit Diesel distributorships and has for more than 30 years. Once around the dining table I asked him the same question and he replied that there is no difference in the blocks or the internal parts between 'marine" and auto. After having looked inside a few motors I tend to agree. I think the prices are so high for marine parts simply because people will pay them. I think that's one of the laws of economics, eh?

kilowatts

RogersJetboat454 · Aug 18, 2011

Re: Auto vs. Marine motor assemblies?

kilowatts said:
I think the prices are so high for marine parts simply because people will pay them. I think that's one of the laws of economics, eh?

Also figure in the fact that you have a middleman (VP, or Merc) between GM and the dude/lady selling you the parts. Personally If I wanted to put GM parts in the engine, I would be stepping up to the parts counter at the closest GM dealer with a part number, and candidly tell the person working the counter "it's for a boat"

Kitakojo · Aug 18, 2011

Re: Auto vs. Marine motor assemblies?

Thank you all for answering my question on can I take a VP 225D and replace it with a standard automotive 305/350 blk. My father an old time boater Mid 60's from Cedar Rapids IA stated his friend would yank the motor out of his car and put it in his boat for use on the weekend did this while he was rebuilding the original boat motor. He than on Sunday evening put it back in the car for work during the week. Sounds crazy but things were a little different back then exspecially when it came to impressing the ladies. I'm one whom is not afraid of installing a 350 auto engine in place of the VP 305. Used 350 blk/complete engines sell for $300 all day long around here.

boattoy · Aug 18, 2011

Re: Auto vs. Marine motor assemblies?

its not the motors that sets em apart. its the trimmings. exhaust system, cooling system, coating of parts to prevent corrosion/rust. specialty electronics to prevent sparks arcing around the engine. there is a reason why all the common marine engines are based off truck motors, reliability. cam differences are just because the motors run lower rpm. not much different then a "rv" cam.

DanMC · Aug 18, 2011

Re: Auto vs. Marine motor assemblies?

:redface: We want to think that they are different but for most part they are same motors...it's conforting to think that "marine" has magical differences because we pay so darn much for them

.
Dan

glmoore001 · Aug 18, 2011

Re: Auto vs. Marine motor assemblies?

I noticed that the blocks on the hundreds of busted boats on Ebay were mostly 351 fords and 350 chevys. So I had planned to buy a boat with a good hull and a wiped motor, rebuild (or replace a cracked block, there seems to be plenty of those around) with an auto short block using the marine parts on the outside. Now it seems I also have to use the cams and heads out of the marine engine right?

Auto vs. Marine motor assemblies?

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