Difference between automotive and marine long-block

[MelLandry]

I KNOW this has been discussed before. I tried to search for it, and learned I hate the new search feature.

Moving on...

What is the difference between a marine and automotive long block on a Chevy 350? This is a NEW long block, not a referb.

I know the drain plugs would need to be exchanged, and I know the crank is different.

What is the difference in the crank? What does this effect? What is the risk of using the automotive crank?

This is a 19.5ft run-about that I DON'T usually pull people with, RARELY run wide-open, and mainly just cruise around in.

Are their any other differences?

 

[Bondo]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

Well,............

That's the Core Plugs,..... Or to some people, the Freeze Plugs,....
That need to be Brass,+ Not Steel.........

And,....... There's No Differences in the Crankshafts,...... Between Automotive,+ Marine anyways...........

Buy yourself a Long Block 350 for a Truck,+ You'll be Happy with the results........

Just be sure to Match the Vintage of the Components........

 

[DangerDan]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

Here are some suffix codes for various engines.

http://www.nastyz28.com/spmenu.html

It is possible to miss match components giving more horsepower than originally specified for a particular block casting.

I'm not sure if who you are buying an engine from will match certain block #'s to a job but it's a good practice and nice to have the information prior to purchasing a block that may be under rated for your service.

I would also consider a balanced crank and see that the bearing clearance and other tolerances are followed closely.

 

[michaelrj9]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

I thought gaskets need to be changed out
I thought I read somwhere that the cams are different also.

Someone who actually knows what the differences are if they could post it because I would like to know what is different also.

Thanks
Michael

 

[Rock Hall]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

I was told the cam is different, because you dont run a marine engine the same as a car. I cant remember the details.

Isnt a different head gasket used also?

 

[Scaaty]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

Yep, cam, not crank......might need a little info relating to gaskets. You in salt, Raw cooled, Fresh closed..? ? ?

 

[ramster]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

What year is your boat? Typically, the chevys are the same prior to 86' where they used a two piece crank seal, after 86' they switched to a 1 piece, and I think the flywheels are different. If you can try to get a later model with a roller cam. There is a slight difference in marine cams, but you could get away with a stock automotive type, most are short duration and should make around 250 HP in a 350, if you are looking at a GM Goodwrench type replacement, just get one for a truck, it should have a cam that favors low end torque. If you are considering a used car motor, just put in brass freeze plugs, and if it is an older engine with some miles on it I would put in a new gasket set for the heck of it to avoid any nuisance oil leaks.

 

[MelLandry]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

Yep, cam, not crank......might need a litle info relating to gaskets. You in salt, Raw cooled, Fresh closed..? ? ?

Run MAINLY in fresh, but the boat is trailered, so it is occasionally taken on vaction to salt. It is raw water cooled.

Hopefully when Don wakes up, the can clear it all up for me.

I need to find a channel surfing board so I can be a deity like he.

 

[ramster]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

If you are going to run salt water, then I would spring for marine grade gaskets.

 

[MelLandry]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

What year is your boat? Typically, the chevys are the same prior to 86' where they used a two piece crank seal, after 86' they switched to a 1 piece, and I think the flywheels are different. If you can try to get a later model with a roller cam. There is a slight difference in marine cams, but you could get away with a stock automotive type, most are short duration and should make around 250 HP in a 350, if you are looking at a GM Goodwrench type replacement, just get one for a truck, it should have a cam that favors low end torque. If you are considering a used car motor, just put in brass freeze plugs, and if it is an older engine with some miles on it I would put in a new gasket set for the heck of it to avoid any nuisance oil leaks.

It's a 78 with the two piece seal. It is a brand new GM replacement for a truck with a two piece seal, so hopefully I'll be good to go.

So since this engine is the one built with the 2 piece seal, everything else should be correct... is that what you're saying?

My next question is: With this new engine with slightly different components (and the fact that I'm going from a 305 to a 350) how am I supposed to figure out what WOT should be so I can prop it correctly?

 

[bjcsc]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

Hopefully when Don wakes up, the can clear it all up for me.

Doubt it. Don S strikes me as a purist. I think he would/will advise you to get a proper marine longblock to begin with as opposed to trying to rig one up...of course I suppose that could be viewed as "clearing it up" for you...maybe we'll see...

 

[KaGee]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

The cam for a GM truck is ground very close to the marine cam. Do not use an automotive cam. The power curve is different and you'll possibly experience water intrusion with an auto cam.

The "purest" will also advise you to use "marine" headgaskets. In freshwater, you will not see the difference IMHO.

Re-use your water circulation pump from the old boat motor or buy a new "marine" one. Do not use an automotive pump there. Same with the fuel pump. Just swap over all the other stuff.

Regardless of watever propaganda BS you read elsewhere, the blocks and heads are all the same. There is no difference in rods, pistons, crank, lifters... it's all GM Chevy "stock" parts.

 

[imported_Tinboat]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

..Competitions Cams H.E. 260 is the cam grind used by mercruiser (just under a different part number)...the head gaskets MUST be changed to marine apps., along with the freeze plugs....cylinder heads are something to take notice of also, #182 castings are preferred, as they are a truck style head, and produce more torque and power at lower RPM, PLUS they have a thicker deck, and are less prone to cracking under the temperature fluctuations experienced by fresh water cooling systems.
...and ALL Mercruiser crankshafts are steel cranks, not cast...(more strength, elasticity).....good luck !!!

 

[ramster]

Re: Difference between automotive and marine long-blcok

Re: Difference between automotive and marine long-blcok

You said this is a long block so you already have new heads, if not you'll find that the 305 heads will fit, but they have small combustion chambers and small valves. 305 heads on a 350 will likely give way to high compression,and poor flow because of the smaller valves. As for the prop, what are running now? If you currently run a 21 you should be able to run a 23. WOT RPM is the same around 4800 for a flat tappit, 5000 for a roller cam.

 

[walleyehed]

Re: Difference between automotive and marine long-block

"Regardless of watever propaganda BS you read elsewhere, the blocks and heads are all the same. There is no difference in rods, pistons, crank, lifters... it's all GM Chevy "stock" parts."
That's the B.S.....
The engine is not simply shipped to mercruiser for decal application. In fact, the internal components come seperatly, and are ballanced as a rotating mass. Yes, "some" of these parts are GM, others are not.
Atleast when I was shipped to school on them, that's how they were built.

 

[John_S]

Re: Difference between automotive and marine long-block

"...and ALL Mercruiser crankshafts are steel cranks, not cast...(more strength, elasticity)..."

According to Dennis Moore, all standard SBC marine engines came with cast cranks.

 

[tommays]

Re: Difference between automotive and marine long-block

Well i pretty sure they dont blueprint the 3.0 and MOST of the motors come out of mexico at this point



I know they build the 6.2 and other high end motors in wisconsin

Gm puts the specs and all the OEM builders right on there sight

A LOT of different stuff 2 bolt main 4 bolt main ect ect etc

http://www.gm.com/automotive/gmpowertrain/engines/specialized/marine/index.htm


Tommays

 

[ramster]

Re: Difference between automotive and marine long-block

I helped a friend of mine do a 4.3 for his Bayliner, it was a junkyard motor from a chevy van, he used all automotive stuff, which is much cheaper than anything that says Mercruiser on it. The cam is an Edelbrock Performer, same one you can put in a car, or truck. The boat runs great, he saved a ton of money, and uses it almost every day, no problems. He did use the marine carb, and electrics, which I would recommend, but there are many parts from Napa that will work just fine.

 

[KaGee]

Re: Difference between automotive and marine long-block

Dude, just put the truck crate motor in it and call it a day... that boat will rot out from underneath you or the drive will detonate before you blow the motor up... providing you maintain it.

 

[MelLandry]

Re: Difference between automotive and marine long-block

I know it's been a long time... but I wanted to give everyone who helped me out here (and on other posts) a big...

THANK YOU!!!

Yesterday was her first "sea trial" with the new power plant and she ran like a dream.

This breaking-in thing is NO FUN. It's so hard not to open her up and see what she can do. Only had an hour on the water yesterday before I lost daylight. I hope to get her up to 10 hours over the weekend. I'll try to post some pictures after this weekend.

And THANKS AGAIN! You guys are the best resource on the net.