3.0 omc to 4.3 cobra

metal249 · Nov 5, 2009

I have a 17 ft w/3.0 omc cobra and I'm looking to repower. I have three questions; If I switch the 3.0 with the 4.3, will it bolt right up? Will it handle the power? Can I run a radiator, and set it up like an automotive engine, and just bypass the whole raw water system? Any help would be appreciated.

Bronc Rider · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

The short answer is no. It will handle a 4.3's power though.
Why do you want to bypass the raw water system?

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

I was thinking about just putting a GM 4.3 in place of the 3.0. Just use headers and a muffler out the back and a radiator with an electric fan to cool it. Does the outdrive need water flowing through it?

Bronc Rider · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

There is a few problems with what you are trying to do.
If you run headers you would need marine units $$$. Regular headers do not run water thru them and they would get way too hot under a doghouse resulting in a possible fire. The drive does need some cooling but maybe a drive shower would be enough, I don't know. I really cant see how you would mount a radiator on a boat and get enough air flow to it.

Bronc Rider · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

I also want to point out that none of the accessories on the auto engine can be used in a boat. You will need all marine accessories to not blow up your rig (and yourself).

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

Well thanks for the advice, I guess there just is no "cheap" way to repower.

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

If I get the exhaust manifolds for the 4.3 omc, will it work with the 3.0 cobra outdrive?

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

I'm working a restore of a 19ft cuddy with a 110hp I/O 4 cyld volvo. Put it in the water the day and got 32 mph and found out I'm over proped so I might be looking at more speed when I get the right prop. But anyways...One day I will want more power (the 4.3). From everything I have read on here about I/O's, the best thing to do is buy a boat "with that power" or already "setup for the power". My dad has told me that the best two days in a mans life is the day he buys his boat and the day he sells it!!!...lol...Yes! you are in a expensive hobbie.

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

Have you thought about the outdrive gearing? It will have to be changed as well.

Please becareful, some of the things you are thinking with the auto parts in a marine environment are DANGEROUS!!!!!!!!! MUCH thought and study should be put fourth before buying anything!

To answer the question about the manifolds...No they wont.

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

I picked this boat up very cheap, and I have already easily gotten my money out of it. It's a project now, I have already replaced the rotten floors with fresh treated ply. I am going to make this thing really nice, but I know it will take a while. When I am done though, I will have exactly what I want in a boat.

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

Yep I am doing the same with mine. I got mine cheap knowing I had to rebuild the engine and interior. When I'm done and I've used it some I will use it as a down payment for my next boat with a 4.3 already installed.

There is a HUGE amount of things that have to be "over come" when going up on cyld numbers on a boat with a I/O.

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

So is the cobra outdrive for the 3.0 different than the cobra 4.3?

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

It's geared defferant. But thats all I know. I have a Volvo Penta setup. Dont know what other changes would have to be made for a merc or OMC. But the gearing does have to be done with any outdrive no matter the mfg. Look around ebay for new gears. Your heart will drop when you see the prices.

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

O..and Congrads!!!...You just with up in your members class!!! And with this post so did I.

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

The gearing shouldn't be an issue, I plan to rebuild the outdrive if I use it, so I can probably just build it with the correct gearing.

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

you might...I can take my outdrive and move it up from a 4 cyld to a 6 with new gears and thats all. Sorry but I dont know about yours. Do a search for it. I can just about bet somebody has already asked and got a anwser for that.

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

I have been searching for a very long time. No one seems to know much about omc conversions. I am definitely not paying $160 an hour for a boat mechanic to figure it out.

Paul Ryan · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

Check this.

http://forums.iboats.com/showthread.php?t=56256

Bronc Rider · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

You could find a boat like the other poster mentioned and switch it over. If thats what you do, it would be better to switch it over to a more common Merc. I have done the cobra to Merc swap twice. Its pretty straight forward swap if you take everything. And I mean everything including the wire harness. I even swapped gauges. If you can have both boats at the same location its a breeze. There is also a fair amount of rotten boats for sale that could make it rather cheap.
As far as your outdrive, I think SEI recently released some type of adapter that can be used to bolt up one of their alpha clone drives to your cobra. Not sure as to how its done but, rebuilding an outdrive comes out to be more expensive than buying a brand new one. Just order it with the correct gear ratio.

metal249 · Nov 5, 2009

Re: 3.0 omc to 4.3 cobra

Is the hole through the transom the same? Does the transom need to be reinforced? It seems very easy if it's all just bolt on. I'm good with cars but I don't understand outdrives yet.

3.0 omc to 4.3 cobra

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