What makes a marine engine a MARINE engine

[BigBoatinOkie]

Hi there, I've been thinking about uprgading from a merc 5.0 to a 5.7. My question is, can I use any 350 block or is there something special about a marine engine. I'm not sure what makes a marine engine special. Some education please. Thanks.

 

["G"]

Re: What makes a marine engine a MARINE engine

As far as the block goes, not a lot about it is marine except brass soft plugs verses steel. The "marine" part comes with accessories like starter, alternator, carburetor to name a few. Electrical components are spark proof per se', the timing isn't vacuum advanced and the carb doesn't flood to the outside but down the throat. It used to be the fuel pumps were different but most use electric now.

If you use the parts off your old marine engine and put them on your new block you should be OK. Remember to use a cam that is supportive of your distributors timing capability and the carbs air to fuel ratio. A vacuum guage will be your friend at start up.

 

[bruceb58]

Re: What makes a marine engine a MARINE engine

Marine water pump
Non steel head gasket
Cam from a truck motor will be fine.

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

Sweet. Thanks guys. I'll definately be using everything I possibly can from the 305.

 

[jerryjerry05]

Re: What makes a marine engine a MARINE engine

If your gonna use it in freshwater then the cam and carb,intake manifold and fuel pump are the main things.The flywheel will probably be different depending on the year.
Your not gonna notice much difference between a 5 and a 5.7 Jerry

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

I was thinkin 5.7 with vortec heads. Shouldn't that make a pretty substantial difference? Wont that be a good 50 hp increase. Mine's a 228 hp.

 

[Bondo]

Re: What makes a marine engine a MARINE engine

I was thinkin 5.7 with vortec heads. Shouldn't that make a pretty substantial difference? Wont that be a good 50 hp increase. Mine's a 228 hp.

Yes....

 

[mkast]

Re: What makes a marine engine a MARINE engine

Look in your local library for a copy of Dennis Moore's book on small block Chevy marine performance. The first section is the difference between marine an auto engines.

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

Thanks bond-o. In my experience, which is only with chevy trucks, the 305 was a bit of a turd compared with a 350, especially vortec.

Thanks mkast, I will have a look at the book you mentioned.

 

[northernmerc]

Re: What makes a marine engine a MARINE engine

If I were building a marine engine, I would balance the bottom end moving parts. Unlike in automotive applications, one often runs a marine engine at full throttle. Balancing should reduce vibration and prolong the engine life.

 

[Isaacm1986]

Re: What makes a marine engine a MARINE engine

I upgraded my 5.0 to a 5.7 liter last year in my bayliner capri. Worked just fine, I had a RV cam in the motor, and it will bolt right up to your existing outdrive. Just use as many of the parts from the 305 and you will be good to rock!

 

[castaic piper]

Re: What makes a marine engine a MARINE engine

If you go with a vortec the intake has a diffrent bolt pattern.

 

[mylesm260]

Re: What makes a marine engine a MARINE engine

I was thinkin 5.7 with vortec heads. Shouldn't that make a pretty substantial difference? Wont that be a good 50 hp increase. Mine's a 228 hp.

You can use lookup truck hp numbers to get an idea of what you might expect.

a pre-vortec 305 makes about 200 HP in a truck.

Because of better exhaust and intake, boats always make about 15% more HP, given identical components (heads, cams, intake, carbs)

so 200HP +15% is 230, which is bang on with what you have.

a vortec 5.7L makes 255 HP in a truck. adding 15% works out to 293 HP.

So if you took a 255HP 5.7L vortec out of a truck and simply dropped it into you're boat, it would make 293 HP roughly.

 

[Isaacm1986]

Re: What makes a marine engine a MARINE engine

You can use lookup truck hp numbers to get an idea of what you might expect.

a pre-vortec 305 makes about 200 HP in a truck.

Because of better exhaust and intake, boats always make about 15% more HP, given identical components (heads, cams, intake, carbs)

so 200HP +15% is 230, which is bang on with what you have.

a vortec 5.7L makes 255 HP in a truck. adding 15% works out to 293 HP.

So if you took a 255HP 5.7L vortec out of a truck and simply dropped it into you're boat, it would make 293 HP roughly.

Yes there is a HP difference when dropped into a boat, and it will make a difference. but you will not be pushing 293hp at the prop, the motor may out out that much. but it is going to drop by 8-10% at the prop. When I did the 5.7 liter swap in my capri, I figured a 5% increase in HP over what it had in the truck.

 

[mylesm260]

Re: What makes a marine engine a MARINE engine

Here is a GM write up on the vortec 4.3

http://www.bucksengines.com/Data/24.pdf

it specifically compares the truck vs marine version.

note page 4.

it shows HP output as well as exhaust back pressure and intake restriction.

if you read through it, ALL other performance related components are identical, the ONLY factors changing the HP are the intake and exhaust.

And if you think about it, it makes prefect sense.

cars are built to be quiet and pass emission.

They have air boxes and air filters and resonators on the intake plenum.
and they have catalytic converters and resonators and mufflers on the exhaust side.

 

[Alpheus]

Re: What makes a marine engine a MARINE engine

If I were building a marine engine, I would balance the bottom end moving parts. Unlike in automotive applications, one often runs a marine engine at full throttle. Balancing should reduce vibration and prolong the engine life.

I just did this to an engine I just built. The crank was balanced at the machine shop. I then weighed all the rods and found the lightest one and took material from all the other rods to match. It does make a heck of a differnce that you can feel in a car, but this is the first marine engine I've built so I'll have to wait and see if I notice...

 

[BigBoatinOkie]

Re: What makes a marine engine a MARINE engine

Wow, thanks guys, lots of good posts. My objective is to build an engine that makes good hp but remain very reliable. I will have access to a very cheap 350 block out of an 85 silverado swb. I will get some vortec heads from a wrecker yard probably and take it all to the machinist. I'm thinkin probably an edelbrock performer rpm and edelbrock carb. What size carb and cam would yall recommend. Remember, reliability is a key.

 

[mylesm260]

Re: What makes a marine engine a MARINE engine

my recomendation would be this:

#1. don't go mixing and matching old blocks with new heads.
#2. don't rebuild if you don't have to.

source a running, low km complete truck engine and marineize that.

you will be able to use the stock cam that came with the truck vortec.



While you CAN put vortec heads on an old engine and it WILL make an improvement. The vortec engine has several components that are different and work best as a matched set.

The pistons, and cams are different on the vortecs.

truck 350's are a dime a dozen in running shape, find one with low miles on it and you're laughin'.

If you REALY want a fresh motor, then rebuild it. Rebuilding a motor that's already running is MUCH cheaper than rebuilding a motor that's run into some major issues.

You won't need to deal with all the expensive things like line-boring and over-sized pistons.


You can even use the stock truck water pump, head gaskets and frost plugs if you install a heat exchanger.

 

[270win]

Re: What makes a marine engine a MARINE engine

Plus, a later model (post 87) block will have a one piece rear main seal and the provision for a factory roller cam. That will add HP, reliability and save you money on the build. And they're a dime a dozen...

 

[mylesm260]

Re: What makes a marine engine a MARINE engine

And, not that it's a huge deal, but you also get a balance shaft out of the whole deal... a little more smoothness is never a bad thing.