NooB with Motor swap Questions

[Concealed45]

Hello everyone, I am thinking about buying an I/O with a OMC 305ci.

The motor doesnt run and I am not really wanting that big of a motor, all we do is Fishing, no interest in skiing. I do motor conversions on cars and I have a few GM 60° Fuel Injected V-6's sitting around. My question is being new to inboards what would it take for me to swap the 305 for a V-6 ? I was thinking of trying to do a self contained cooling system also if it is feasable. Please help with any info yoou might have.

Mike

[gonzo]

Check out the other threads addressing that same issue. Marinizing an automotive engine is often more expensive than getting a rebuilt unit. There won't be a considerable difference in fuel consumption between the 5.0 V8 and the 4.3 V6. If you run the boat at the same speed, they will be producing the same HP. The water pump in the outdrive cools the gear oil so you have to keep that.

[Concealed45]

Thanks for the reply, I tried to search for other threads on the subject but had no luck. The motors I have are 2.8 v-6's, I am no stranger to dapting motors to mate to mis-matched transmisions for cars and have CNC mills and a CNC lathe in my garage to fab thing I may need. I just am a stranger to the inboard and how the cooling system works and is routed, that is why I thought about doing a self contained cooling system using to outdrive pump for a heat exchanger. Again I am new to this and my thoughts may be way off base. I do have a couple 350's sitting in the garage if it would be easier to stick with a GM V-8. I just would prefer a modern injected motor.

[gonzo]

You would have to fabricate exhaust manifolds and a Y pipe to fit them. That is the Y that connects the exhaust to the outdrive. The 350 is a straight replacement for the 305. You can reuse the manifolds, carburator etc. All the electrics have to be shielded and you need the correct camshaft. Fuel injection doesn't make as much of a difference in a boat as in a car because the load is fairly constant.

[Concealed45]

Maybe I will make it easy on myself and stick with a v-8 then, The 305 may still be okay, I will just need to do a compression test on it and see why it wont run if it does have compression. He said it quit on him on the lake and he has replace all the ignition components an outdrive pump because it seemed to be getting hot.

What is the differance in the Cam between car and boat ?

Thanks for you input !

[gonzo]

A marine cam is almost identical to a tow truck cam. They are designed for maximum torque. Marinized engines have Stainless exahust valves. When you stop the engine the exhaust is under water so you get some steam backing up. It makes them last longer. Check the exhaust manifolds. That is where the water gets out. If they are clogged, the water won't circulate and the engine will overheat. Also the power steering cooler may get clogged.

[Concealed45]

Thanks, When I get the boat to my place I will give all that stuff a good looking over ! Will a standar SBC gasket set work on this so I can pull it apart without tracking down hard to find gaskets ? Also I noticed the firing order cast on the manifold was not standard 18436572 SBC Do they use a special crank/cam combo just for marine apps ?

[gonzo]

It should be the same unless you have a reverse rotation engine. That would be really unusual with a IO. They always get reversed in the gears if they need it. You are in Colorado, so with fresh water using to cool the engine is no big problem. In fresh water the exhaust gasket doesn't need stainless mesh instead of regular steel either. You can use a standard gasket set. The circulating water pump has a stainless shaft on boats. I think the new ones on cars do too. Oil pumps are high volume, and they need to fit the oil pan. They pans may be deeper so the pickup is longer.

[Concealed45]

Another question on the fuel injection I just though of. On our outboards over the years we have had issues due to the altitude with getting them to run at any speed in our high mountain lakes. Is a carburated 4stroke going to be less finiky or would FI be a solution ?

[gonzo]

The manual has the jet sizes for high altitude. They are bigger

[Concealed45]

Thats what I figured, Thanks again for all the help ! :D

What is really entertaining me is that both my Dad and I were nicknamed 'Gonzo' growing up ! :cool: So I figured I found the right guy to help me !

[gonzo]

We should start a club :)

[Concealed45]

LOL ! Ya, big club to !

Maybe once I figure out how this whole inboard setup works I will work on a Supercharged 3800 conversion for it since that is what I am used to putting in cars now. I think they have stainless valves to ! Might be a fun experiment ! 280hp V6 yeeehaaa !!

Do you know of any good sites with an explination of the cooling system routing and such ?

I will be back with more questions when I get the boat here !

[WestVanHan]

From memory,reverse FO on sbc is 1-2-7-5-6-3-4-8.

Is that what you have?

[Concealed45]

That kind of sounds like it. Not sure as the boat is not in my hands yet, probably a week or two before I really get to dig into it !

[gonzo]

If the firing order is on the intake manifold, it could just be from a reverse turning engine. Crank it and see which way it turns.

[Concealed45]

Do you mean yhe manifold could be from a different engine and the wrong firing order is on it ? Wouldn't that be funny if thats why he has not been able to get it to run !

[broke_not]

Marinized engines have Stainless exahust valves

Marine engines can have stainless steel exhaust valves. They aren't *automatically* equipped with them.

;-)

[gonzo]

The firing order should be standard with a sterndrive. Unless this is a very ancient engine, they all have Stainless exhaust valves.

[broke_not]

When you stop the engine the exhaust is under water so you get some steam backing up.

So what happens when you shut the engine off and it stops with several of the exhaust valves open? Where's the steam going to go? It's going to travel right past those open valves and right into the combustion chamber/cylinder.

I suspect that the marine engines that do use stainless or inconel, (and no.....they do not all use stainless or inconel), use them for their ability to withstand higher temperatures for longer periods.

;-)