Max HP for a 18' I/O Supersport?

[1hoser]

Hi folks, I am new to the forum but can already see the benfits of everyone's knowledge and experience. Anyway I bought an 18' foot I/O Supersport with a bad 120 hp OMC. I am looking to repower it with a Mercruiser and was wonder max the I/O I can put in it? I am looking at either :

http://northbay.kijiji.ca/c-cars-ve...ruiser-470-Engine-Outdrive-W0QQAdIdZ187208869

or

http://northbay.kijiji.ca/c-cars-ve...cruiser-Motor-And-Outdrive-W0QQAdIdZ202063238

Thanks in advance.
Ryan

 

[Huron Angler]

Re: Max HP for a 18' I/O Supersport?

You don't want to get a Merc 470...do a search on iboats and read all about them, they have issues. The guy claims it has a new heat exchanger but still probably one to avoid.

I am no I/O expert but I'd look for a nice Merc 120-165 for an 18' SS.

 

[Kainon]

Re: Max HP for a 18' I/O Supersport?

I dont own a 470/170/185 etc.. big 4 cyl engine, but have worked on a few professionally and have to say I'm still on the fence.

Yes there are a few drawbacks about them but for the 4cyl-HP/torque ratio they're pretty good..

I love my inline 6 but in an 18' would stick with a 4cyl for space reasons.

You "could" go with a V6 4.3L engine if you really want some HP.. 175-210 depending on the package.

My 21' is rated @ 165hp, but the new 21's are 210hp !!!

me being a GM guy would go with a newer 135hp/140hp 4cyl not a 120.
(it's not just 20hp less.. )

a V6 might be too much weight though..

You could close up the transom all together and put on an outboard bracket and go with a nice 150hp Evinrude.. I bet you'd hit 50mph.

have fun !!!

 

[Kainon]

Re: Max HP for a 18' I/O Supersport?

By the way.. You could get a new 140hp 4cyl (OMC/Mercrsuiser Long Block) and bolt up to your OMC hardware)

Same process as replacing the 120hp Mercruisers with newer 140hp ones.
there is a slight difference with the Flywheel, and the intake/exhaust manifold is different from that 120 to the new 140..
everything else should be fine.

 

[Gnarly]

Re: Max HP for a 18' I/O Supersport?

I like my 470/3.7
lottsa jam, light weight and great fuel mileage
havent had a lick of trouble with it so far (knock on wood)

 

[Bwana Don]

Re: Max HP for a 18' I/O Supersport?

My 18' offshore (1971 aluminum) is rated for 140 hp max. Your ID tag should give a max hp on it.