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Performance expectation 350

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richiev8

New member
Hi,

I have recently purchased a larson 190 cuddy, powered by a mercrusier 350, alfa 1 drive. The engine was origionally a LX5.0 ( 305) and from what I can find 220hp.
The boat is now fitted with a 350 crate engine from goodwrench, there base engine rated at 290hp in a car with headers.
This is my first stern drive boat, anyone ideas on what performance I should expect from this combo in the 19 foot hull??
Looks like the cam spec in the crate engine is the same as the marine version, from what I understand the only thing that were not swapped from the old 305 were the marine freeze plugs and head gaskets.
Has anyone else gone down this path? I would assume a performance gain given increase torque and HP?
currently running a 14 1/2 inch prop 17 p

Thanks Richie
 
Well, first of all, the crate engine will be using the full dished pistons, of which means for YOU, that you must use the Marine Ignition curve.... (of which you must do anyway).

Secondly, the crate engine's HP is rated at an RPM whereby we do not operate our marine engines.
The Ignition advance will also be held back now, so don't expect to see 290 HP. (it will still be plenty for a small 19 foot boat)

The camshaft profile may not be ideal for the Marine Exhaust system (reguarding water reversion)..... learn what you can, and take precautions.

I'd double check what GM is using in the crate engine for head gaskets! If the fire rings are not suitable for Raw Water Cooling, you will eventually have issues.
If the engine is still fresh, this may be the time to install a Closed Cooling System (this keeps the coolant PH Balance correct).

As for the casting core plugs...... if you maintain the RW Cooling, the standard core plugs may last a short life.

One of the more critical aspects of this, will be to make sure that NO Automotive Ignition Timing Specs are used.
One good aspect is..... this is a relatively small boat for the Auto version engine.

It should offer you plenty of power.


When it comes to prop selection, you must use the WOT RPM test method.
.
 
You should expect a very short life for an automotive engine in your boat. The automotive engine will not last under the sustained loads a marine engine is subjected to.

Wrong core plugs, wrong head gaskets, wrong valve overlap on the cam, Intake and exhaust valves are not stainless, and the engine probably came with the automotive sheet metal which will last about a year.

Pull the engine and sell it. Purchase a marine long block and marine sheet metal.

You need to check the drive ratio and make sure it is 1.50:1
You also will need to re-jet the carb for the 5.7. It will run lean on the 5.0 jetting.
 
re;" only thing that were not swapped from the old 305 were the marine freeze plugs and head gaskets."

If you swapped the carb from your old engine, you will be flow and/or jet limited (305 CFM vs 350CFM requirement). If you used the crate carb, not likely marine rated and a BIG safety hazard.
 
I don't believe that jetting will be the issue made out to be.
A 305 @ X+ rpm will pull about the same CFM as a 350 will @ X- RPM.... and well within the carburetor's CFM range.
The carburetor will be somewhat under-rated for CFM as it is.
(we just recently did some basic CFM math on the forum here)
In theory, the fuel metering will adequately provide for the various RPM and CFM requirements of either.... me thinks!


The head gaskets will not be an issue if a Closed Cooling is installed.
(it's all about the PH balance of River/Lake/Ocean water -vs- E/G/h2o)
Likewise if an automotive aluminum intake man is used.

The casting core plugs will not be as great an issue if the Closed Cooling system is installed.
They'd be more likely to suffer from external exposure, than the brass will...... just keep 'em painted.

As for the camshaft profile re; over-lap and exhaust/water reversion.... much will depend on the exhaust system and back flow prevention, idle RPM, etc.
Center-rise mans and at or above water line thru-hull exhaust w/ flappers...., for example!
I'm not advocating the use of the auto profile camshaft......., just offering a few general thoughts on it.

As I mentioned earlier, if you're going to pull this off, you're more likely to do so in this small 19 foot boat.
 
Thanks for all the advice. I did not put the engine in, was done by a marine shop for the previous owner.
As far as i can see carb, dizzy, manifold water pump have all been swapped over. Will pull a plug check for over lean conditions.
As far as the head gaskets are concerned will probably run with is as its in a fresh water lake here, if i get issues will pull and rebuild, as I own a automotive workshop, so not a major for me.
Have not run on GPS but the speedo is saying about 50mph and pulling just shy of 4500 rpm with the 17p merc vengence prop, was expecting a few more RPM and few more RPM's.
The cam spec look softer than most of the aftermarket marine replacement sticks, risers were replaced when the engine was replaced 5 hours ago.

Cheers
 
this is the piston in the 290 crate, and that GMPP 290/350 is built to pretty much identical specs as 1980's Mercruiser and OMC 260HP 350. The cam will be fine - very similar grind to marine.
M28537083.jpg
 
Hi Guys, thanks for the effort and info, I did the same research before I bought it, thought it would be ok, I would like forged pistons but, have seen cast take abuse in cars.......... and i drive like a Nana now ( and ski like one too):)
 
hystat said:
this is the piston in the 290 crate, and that GMPP 290/350 is built to pretty much identical specs as 1980's Mercruiser and OMC 260HP 350. The cam will be fine - very similar grind to marine.
M28537083.jpg
Click to expand...
You may want to check that again. If the cylinder heads are 64cc chambers, the Flat Top (even with double reliefs) will create a C/R that may not be suitable for a Marine Cruiser engine.
Flat Tops (w/ single valve reliefs) with the earlier 76cc chambers are almost ideal for the 5.7L marine engine.
You'll want to bring the deck height into Quench specs (.038").



richiev8 said:
......... I would like forged pistons but, have seen cast take abuse in cars.......... and i drive like a Nana now ( and ski like one too):)
Click to expand...
Piston material selection is one thing..... piston profile is another.
Let your cylinder head chamber volume help determine which pistons to purchase.

See this ME.com thread on similar topic.

.
 
Clymer is good for only starting fires.

The rest i agree with.

Fresh water only boat, don't worry about the casting plugs and gaskets your good to go.
 
hystat said:
I rechecked - that is the piston - and the heads are 76cc
Click to expand...
Sorry hystat, I was assuming that you were refering to a current SBC crate engine .... of which I'm fairly certain would use the smaller 64cc chambers...... Vortec or No Vortec!

Here's what I come up with under "GMPP 290/350" .
Apparently is uses the 76cc chambers, so that piston would be suitable for Marine use (I'd rather see single valve reliefs).
However, isn't this being advertised as an Automotive replacement?????

images


12499529 - 350/290 HP V8 Crate Engine
The HP 350/290 is GM Performance Parts’ value leading
crate engine, with 290 horsepower @ 5100 RPM, and 326 lb-ft of torque @ 3,750
RPM on 87 octane fuel. The 350/290 HP will provide great long term durability
with its 4-bolt mains, PM steel rods, strong cast aluminum pistons. The camshaft
has .450” intake and .460” exhaust lift with hydraulic flat tappets. The durable
cast iron cylinder heads have 1.94” intake and 1.50” exhaust valves with 76 cc
combustion chamber and process healthy amounts of air to deliver strong torque
across the rpm range along with great mid-range horsepower. The heads have the
conventional 12 bolt intake manifold attaching design used from 1955 through
late 1980.

Master mechanic said:
1... Clymer is good for only starting fires.

2.... Fresh water only boat, don't worry about the casting plugs and gaskets your good to go.
Click to expand...
1... Ah, don't short yourself.
The Clymer pages (when wrinkled up and softened) are also good here:
NOTE: the Clymer pages can preceed the corn cobs... or visa-versa!
1880_town_outhouse.jpg




2.... Ah.... I somewhat disagree.
They will certainly last longer than if in salt water....., but the PH balance of the river/lake water will eventually take it's toll on them.
 
that 290HP 350 is the current base crate 350 that GM has been selling for about 10 years, and continues to sell in long block form for around $1800. All new, made in Mexico, 2 pc rear main seal and almost identical in every aspect to the 1980's Mercruiser and OMC 5.7 260HP marine version.
GM does not warranty it for marine use, but who cares, warranties are not worth the paper they're written on anymore anyways. 290/350 crate would always be my first choice over some locally rebuilt 350 marine engine. pop in the brass core plugs and go boating. It has composite gaskets with stainless fire rings, and the tinware on it is fine for non-salty applications. A couple of rattle cans of black Tremclad will prep it for any environment. The block and head castings have a good reputation. It's the old L48 with the bugs worked out.

I use to work in an engine rebuild shop. If anyone is selling rebuilt 350's assembled with N. American labour for less than $1800, they are cutting some serious corners and no one is rebuilding engines with all new parts. Rebuilding 350's is a thing of the past in my opinion. Even for the best rebuild shops, every 20th motor blows up. Yep...5% rule. I bet these new crates are much better statistically.
 
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