Newbie: 5.7 replacement options

[Hodge]

Hello everyone. I just purchased my first boat, a 1987 Sea Ray 210 bowrider. I has the original 5.7L Mercruiser engine, outdrive etc. The previous owner let his son use it a few years ago and the son did not winterize it and the block has cracked on both sides. Working on a small block chevy motor is not a problem for me. I have rebuilt 2 that are still running, so since I wasn't intimidated by the motor issues I was able to get a really good deal on the boat. Being a gearhead by nature, if I have to build/rebuild a motor for the boat then I want to add a few more ponies.
:smt100
How can I find out what HP level the outdrive unit can handle?
Also, thinking about going with vortec heads to help ad power. I've used them on a car motor before so I know the intake is different. Are there any boat specific things that would be different when using the vortec heads?

I know the cam profiles are different due to the different operating conditions like cruise rpm and more WOT than a car but....
What other items make boat motors different than car motors?

Thanks
Hodge

 

[sprink56]

Welcome to the "Club".

Let's see if we can answer some questions here.

Since your boat is an '87 it has an Alpha Series I drive. In good condition they are good for about 300~325 HP.

As a suggestion, consider buying a marine long block available from several online as well as possibly local sources. You can opt. many times for a more performance oriented camshaft which in "gearhead" lingo for a marine application gives you a bit more lift as opposed to a lot of duration. The goal is to make the torque curve as flat as possible and keep the RPM under 5000. You can find good ones shipped to you for around $1500.

If you really want to build a great boat engine, find a good 5.7 block, do all the normal stuff like line bore it and hot tank it. Buy a kit to take it to 383 by using the stroke of the old 400 cu. in. small block using the 4" bore (+ maybe .030") from the 350. This makes a very nice torque motor and responds well to things you would normally do to a 350. Beware that this kind of power in a light bow rider can be big trouble in the wrong hands.

I have built 383's that make 375 HP and 400+ ft lbs of torque.

A marine engine uses brass freeze plugs, heavy duty bearings through out, a special water pump that has all stainless parts as well as double roller timing chain. A marine engine is under a load 99% of it's service life so don't scrimp on anything.

Vortec heads are a plus if you can match a manifold. As for carbs..I'm partial to Holley Mechanical Secondary square bore 4150's at 600CFM for a 350...750 CFM for a 383....marine version of course.

I would suspect that the exhaust manifolds are probably rotton if the owner didn't even bother to winterize the engine. Figure on new ones for a new engine.

Have fun.

John F.

 

[Hodge]

Thanks for the info. What is the weak point of the outdrive? Is there a certain part that when replaced allows more than 325HP. I think I saw that the motor originally had 260HP. Does that sound right? If so, then getting to 300 shouldn't be too hard and that would still leave me plenty of safety net before reaching the limits of the outdrive. I don't think I have to worry about the too much power in a light bowrider. From what I can find my boat is 3000lbs. not exactly light by today's standards.


I'm working on getting the motor out this week and the plan is to see what the condition of the rotating assembly is and if that all checks out OK then I'll get the crank checked out and polished, install all new rings and bearings into a new block, assuming I can find a standard bore block and don't have to buy new pistons for a .030 over block. If I can not reuse the rotating assembly then I was planning to stroke it to 383. Thanks for verifying for me that it would be a good idea. I have a 383 in my Camaro so I'm familiar with them. Either way I'll probably just pick out a cam kit that will put me around 300HP. Which makes me curious, how are HP ratings for boats done. is it like a car where it is flywheel power with all accessories attached?

One more question. What makes a marine intake manifold different than a automotive one. I looked at vortec marine intakes and they look exactly like the car ones that are 1/2 the price. I can only assume there is something different on the inside that I can't see.

Thanks for the help.

 

[lime4x4]

The marine manifolds have lined coolant passages

 

[HUMPH]

ebay....

 

[Hodge]

The marine manifolds have lined coolant passages

If I only run in freshwater is this necessary?

 

[sprink56]

I have run aluminum Edelbrocks in salt water for years with no problems...just flush every time you use...even in fresh water...gets the silt out.

The weak link in an Alpha is the upper gear case. Not only the gears but the case its self....it can't stay in shape with the pressure. Compare it to trying to run a stock Vega rear end behind a V8. It will live until you push it.

A good combo I have used in the past that makes a strong runner in a boat is to use the cam that was used in the 327/300 Horse engines from the late '60s. Great idle and super low and mid range...pulls strong up to 5000 RPM. Stay with 1.94 intake valves to keep velocity up....keeps the torque curve flat. Crane makes a reproduction version in their "Blueprint Series". The Holley Double Pumper 600 CFM on a square pattern intake works great right out of the box. The original Q-Jet throttle hook up works with very little modification.

Have Fun.

John F

 

[Hodge]

That's great news. Now I can really start planning my engine out. Thanks John.

 

[sprink56]

You are welcome Capt.:thumbsup: