i/o vs outboard HP equivalencies

[Acer2428]

I bought myself an i/o, but have decided to most likely sell it and get myself a boat with anoutboard. And, since the ev/johnson seem to be the most common on older boats, I thought I'd ask here.

I know there's a large weight difference between a boat with an i/o and OB due to the weight of the motor. Anyhow, I was wondering what the equivalency scale is between the OB and the i/o is on the same boat. Let's use my 18' Mark V for example. To get the same propulsion/plane time as my OMC 190hp, what would I be looking at HP wise in an OB? 100? 115? 150? More/Less?

Thanks.

 

[steelespike]

Re: i/o vs outboard HP equivalencies

Don't know what your boat is like but::
If you are talking about hole shot only I think a carefully setup 100 could match the I/O but wouldn't be practical for all around use.
As far as overall performance Horsepower is horsepower the 150 won't perform like a 190 I/O. It is hard to beat the brute power of an I/O but I think the 150 will match or beat the I/O in hole shot and and with careful setup and propping work in the ball park.If you look in the prop section it appears the I/O folks ( and there are a lot there)are usually looking for better hole shot without over reving in regular use.Whether a 150 outboard is enough for your boat would depend on its actual weight and hull design.

 

[MikDee]

Re: i/o vs outboard HP equivalencies

If you look around on this forum, and check other sources, I think a good running 150hp outboard on a boat like yours, would match , or exceed the performance of up to a 200hp I/O, also giving you a better hole shot, and hold a plane at lower speeds, because of less total weight, and less weight on the rear of the boat.

 

[dingbat]

Re: i/o vs outboard HP equivalencies

Don't quote me on this but I think I remember it working out to be something like a 30% differential.

A 3.0 liter 2 stroke would run circles around a 5.0 Mercruisuer. Yes, HP is HP but the weight to HP ratio gives the distinct advantage to the outboard.

 

[05GlastronSX]

Re: i/o vs outboard HP equivalencies

lets take my glastron sx 17 footer for example. Glastron makes a sx-170 which is the outboard version of the sx-175. they are absolutely identical boats with the exception that one is an o/b and one is an i/o. when i bought this boat in 2005, i had a choice. i looked at the sx175 with a 4.3 carb (190 hp) and the sx170 with the maximum hp rating of 150(came standard with a 90.) my friend has a sx175 with a 4.3 merc and that is what my deciding factor was. I got the 170 with the 150 merc 2-stroke. There is absolutely no competition when it comes to holeshot and outright speed. the 4.3 gets better gas mileage but it does not hold a candle to a 17 footer with a 150 2 stroke outboard on the back. i top out at 56-58 (gps) trimmed high while he's at 50-52. I would put my 17 footer up against a 5.0 17 footer (if possible)and id be willing to bet that the performance would be similar and might edge me on top end or holeshot possibly. i think a new 150 2 stroke v-6 outboard is more comparable to a 200-220 hp i/o and a 200 o/b is like a 250hp i/o. a 115 o/b should be able to compete with that 190 hp i/o. it might not win, but would hold its own.

 

[Acer2428]

Re: i/o vs outboard HP equivalencies

good info, fellas.

I've been looking at older outboards and they all seem to be 90-125 and I was wondering if that would be enough, as I hate the feeling of the tube really holding the boat down.