marine vs auto engine for re power

[ab59]

I am finishing up an engine replacement in by boat and gave the benifit of what I thought I had learned in my research to another about to start his own. I was corrected by a more experienced moderator here and so I began once again to look over the information that I had acquired through investigation and have came to this conclusion.
For every article that suggests that there is a huge difference between Marine and automotive engines that should not be substituted for each other there is an equal amount of other articles that say just the opposite , so who is rite and who is wrong ? Each side seems to have a valid argument and facts to back up what they believe so this leaves me , and I'm sure many others , a little confused.
I could have saved a thousand dollars by using a 5.7 from a truck but did not because of the warnings on this. I am not sorry that I have the engine designed for Marine use but would have most likely used a truck engine if it is the same.
Maybe some one who fully understands this opposing and contradictory action could chime in here and clarify this .

 

[Scott Danforth]

truck and marine motors share the same block and heads, etc.

so get a truck motor, pull it apart, change the head gaskets to marine, and change the core plugs to brass

 

[GA_Boater]

Along with the head gaskets and core plugs, the starter, carb and fuel pump need to swapped over from the marine motor to the now marinized truck motor.

We always say truck motors and the reason is that trucks and boats share the same need for low end torque. A car isn't made for carrying cargo or hauling trailers like a truck is, so they don't have the same torque requirements.

A car motor is not a truck motor.

 

[kenny nunez]

In addition to the above posts the marine engines have a more aggressive cam profile. There was a hard freeze down here years ago and all that was locally available was the GM MR. Goodwrench 350 which were 4 bolt main engines. I replaced 15 of them along with the manifolds. I swapped the cams from the old engine into the replacement and got identical performance each time. That was a good year .

 

[ab59]

Kenny- that is what I thought but now every one is saying that the cam is the same in a truck and Marine engine . I had come to believe that if you wanted to use a even a 4 bolt main engine that you would need to change the cam, freeze plugs to brass , head gaskets , steel valve guides carburetor and starter to equal marine grade . Now it seems that the popular idea is that the cam makes no difference but you still need all the jewelry , starter ,carb. etc and maybe the head gaskets and your good to go .
To little to late for me on this one but if all you need is a truck engine head gaskets and brass freeze plugs then that will be the way I go from now on.

 

[bruceb58]

The cam is close enough between a truck and marine that you would never notice the difference.

 

[jerkoz]

I worked in the engine plant that made all the engines and believe me , there is a definite difference between truck and marine cam . (the profile on a marine cam looks like a racing cam). listen to the idle of a marine engine and listen to a truck engine idle.

 

[bruceb58]

I worked in the engine plant that made all the engines and believe me , there is a definite difference between truck and marine cam . (the profile on a marine cam looks like a racing cam). listen to the idle of a marine engine and listen to a truck engine idle.

I have listened to a truck engine idling in a boat and it sounds identical.

 

[ab59]

And there we have it , the same split opinion . cam is the same or similar to not the same at all , exactly what I am talking about. I guess it's whatever you are comfortable with in the end. For me , since a Marine cam can be purchased for less than 200 bucks about anywhere ( 150 in some cases ) I think that if I do use a truck engine in the future I will put a Marine cam in it . Not to sure about the stainless valve guides though.

 

[bruceb58]

And there we have it , the same split opinion . cam is the same or similar to not the same at all , exactly what I am talking about. I guess it's whatever you are comfortable with in the end. For me , since a Marine cam can be purchased for less than 200 bucks about anywhere ( 150 in some cases ) I think that if I do use a truck engine in the future I will put a Marine cam in it . Not to sure about the stainless valve guides though.

Replace the lifters as well while you are at it depending on the mileage of the engine. Some will say that with roller lifters you would not have to replace them but they are cheap enough to do as well.

 

[bruceb58]

Here are some numbers for the difference between a truck engine and marine. Using a SBC as an example and non Vortec heads.

Truck
Intake Lift-.383" Exhaust Lift-.401"
Intake Duration @ .050"- 194 Exhaust Duration @.050"- 202
Lobe Separation-112

Marine
​Intake Lift-.395" Exhaust Lift-.404"
Intake Duration @ .050"- 202 Exhaust Duration @.050"- 214
Lobe Separation-112

 

[kenny nunez]

More gas in the fire.
I had a 1975 Donzi with a Chris Craft 350. It had a solid lifter .030 .030 cam which one of the chevy guys said was a Duntov design.
A DIY guy asked me why his Mr. Goodwrench was not turning like the old 350. I asked about the old cam. Too late, he threw the old one away.

 

[tpenfield]

Don't automotive 'racing' cams have significant overlap whereas marine cams have relatively little overlap?

I would think a racing cam in a marine engine would invite hydro-locking.

 

[Scott Danforth]

Don't automotive 'racing' cams have significant overlap whereas marine cams have relatively little overlap?

I would think a racing cam in a marine engine would invite hydro-locking.

Exactly. Auto cams have a lower LSA (104-110 degree range) RV and marine are 110-114

Marine motors also top out at 270 degrees duration with wet exhaust. Depending on the motor, you can go up to the 310 degree range with flat tappet and a bit more with rollers