automotive 5.7 vs marine 5.7

rockcity

rockcity

everyday is a chance to get better
Joined
Apr 10, 2005
Location
Greenville, NC
I'm looking around for a boat. If you don't already know, I'm in eastern NC, so the boat is going to be 99% salt water used.

Given that, I would rather have a diesel inboard motor but they are $$$ and the fact they are marine are another excuse to charge double for parts...


So, I'm OK with a boat with the 5.7 or other "standard" V8 option.

My question is, anyone know what differences the marine gas V8 motors have versus the automotive versions?

Specifically the GM auto stuff versus their marine counterparts like the 5.7 mercury or 5.7 Volvo Penta? Last I checked, the basics were all the same but beyond that, any ideas?

Some of the boats will need repowered soon. So, if I can pick up a good rebuilt 5.7 for cheap, it will be way more affordable than paying $12k for a marine version...

Thoughts?
 
no outboard available for the boats I'm looking at

Not to mention, repower with twin 250 outboards is pricy!!! which is why i'm looking at a standard V8 motor; its something I can work on myself and not break the bank.



For cooling, I would replace or make sure it has a fresh water cooling system, so it wouldn't use salt water to cool
 
I looked into this when i was gonna pull the 4.3 out of an old boat we got for my samurai, the actual motors are pretty much identical, but from what i was told the internals are a little different (stronger) since a boat motor is turning higher rpms 90% of the time unlike an automotive motor. The accessorys are all sealed too but that would be as big of a deal to just change out. Dont hold this to fact, but i was told this by a boat mechanic so i figured he should probably know.
 
More research shows that the cams are a little different and the head gaskets have stainless inserts. beyond that, they are the same. Some of the vortec versions have SS exhaust valves to protect against corrosion with being open to the outside air.

Obviously, the fuel system, exhaust, and accessories are different as well as the carb and wiring.
 
as you mentioned, the main difference between the engines in the cam and head gaskets. and as mentioned the external components all are changed also. Some of the newer boats have fuel injection on them now also.

I would recommend staying away from the volvo penta stuff though. From a number of ppl i know that work in the marine industry and have owned boasts with them, the outdrive systems give alot of trouble, and tend to lead to costly repairs. The mercury stuff seems to be pretty good though.

Personally I would go with a true inboard boat if you can swing it. Safety for one, and seems they dont have some of the issues an inboard/outboard boat does.
 
I'd love a true inboard with a jack shaft if I was buying the boat new.

The boat is older, so I'm kinda stuck with what they offered back then. I/O option is only Volvo/Penta. So, beyond that, I'd have to go to a straight inboard, which was available but is more expensive and harder to find. I'd be operating in shallow water (relative), so the idea of the I/O is fantastic as it will allow better access to shallow water without damage. Changing the outdrives may be a reasonable option.
 
Basically, this is the boat I'm looking at, give or take a few years. Outboard only doesn't really work too well and using it in and around the outterbanks and shack may get a little cumbersome without an I/O

27 albemarle.jpg
 
Understandable... my experience is with freshwater only, so I cannot say if the Volvo saltwater equipment is any different. With that being said, for the right price I would buy something with a Volvo outdrive, knowing that there is a potential for repair down the road. I have also found that marine stuff isnt nearly as expensive if you can do the work yourself.
 
Yeah, doing the work myself is key. That's why I was leaning toward the inboard or I/O versus straight outboard as I hate working on those tiny little compact outboard units and I know my way around most truck V8 engines (enough to get by). Plus, parts are insainely expensive with outboards as compared to "standard" automotive parts
 
Dang....I'm gunna have to go to Shack with you! :D
 
Shack is a normal trip with the skiff. This will make it more comfortable with the kids :D Gotta keep them and momma happy!

Plus, the fishing right up the beach at Lookout is fantastic, so I need an excuse for a multi-purpose boat! :lol:
 
That boat looks ready for the Gulfstream and you can beach about any draft boat inside the hook at Cape Lookout. Marine engines have brass freezeplugs, special carbs ( if carbed ) among the other differences mentioned. I would stay away from inboards if you plan to beach it often or run shallow waters though the crowsnest would make it easy to see the bottom before you hit it. Remember a boat is a hole in the water you throw money into, no matter how it's powered :D
 
I can't add anything to the conversation except that I have a 5.7 in my Mastercraft X Star and it has been great! Smooth, quiet, just keep my oil changes around 50 hours and all has been well. Good luck with it!!
 
Ive told you this before 32' center console.
Dual Yamaha 300s.
Fish.
::beer::
::beer::
::beer::


Ok thats my plan anyway
 
You have way more $$$ than me, so I have to keep my toys affordable :D


As much as I'd love the 32' CC, its not nearly as practical for a family with small kids.
 
dream boat.jpg
dream boat1.jpg
dream boat2.jpg
this makes me drool, but I love the sound of the 557 and it appears to turn a boat into a rocket. I think one costs as much as a nice boat w a nice motor though :eek:
 
Last edited:
That 557 is just crazy! Looking at the picture, it looks reasonably sized, but think of a normal LSx engine on top of an outdrive unit, then sitting on the back of the boat! That thing would be massive!!!


Oh, and I love this ^^^^^ Carolina flair on a CC boat is awesome!!!
 
That boat was on CS down east about a year ago for 75k I believe. 2 yrs old and all composite construction. I saw another similar one that was Battleship grey. I'm sure these boats perform as good as they look, esp. coming home when it gets shitty and your many miles offshore.
 
That's a sexy boat!

I think the 557 has a place...once you get 2, 3, and even 4 motors hanging off the ass end of a boat, that's a lot of aggravation. There's multiple steering systems, gotta keep them all somewhat synchronized, they're heavy, etc. I've never seen the price on a 557, but it might be cheaper. The badassness is enough for me :D. I'd like to think you could get way more power than that from that motor though!
 
Back
Top