Engine size for SD 217 IO?

RSTAC1

Curious as to pros and cons of a 4.3MPI Alpha Catalyst 220 HP vs 350 MAG MPI B3 300HP for a SD 217 IO. - Is the 4.3MPI big enough - is the 350 MAG too big? worth the cost? - Fuel cost for each - etc. etc. Thanks for your thoughts and help!

nquirk

Me personally, I don't believe there is too much HP you can add to a boat.

And, I'm an OB guy but suspect the same rules will apply.

There is a misnomer that bigger engines will be cost more to run.  In general it is true, however, if the larger engine allows you to get on plane and cruise there at lower RPMs then the consumption of fuel between it and its smaller counterpart is sometimes insignificant.  I went from a 115HP carbureted engine to a 200HP injected, increased the size of my boat, and still spend the same per hour in fuel.  (If they were both fuel injected, I suspect my spend would've been about 10% more)

I don't know the cost of the extra engine upgrade.  But if you plan to keep this engine and boat for the long haul, and you have a growing family perhaps you should look at the larger engine.

Here are some generic fuel consumption rates in gallons per hour (GPH).

4.3 MPI @ 3000 - 6.0GPH 

4.3 MPI @ WOT - 18.0GPH

http://www.boat-fuel-economy.com/mercury-mercruiser-4.3-262-fuel-consumption-us-gallons

350 MAG @3000 - 7.5GPH

350 MAG @WOT - 23.0GPH

http://www.boat-fuel-economy.com/mercury-mercruiser-350-magnum-5.7-fuel-consumption-us-gallons

You can see in generic terms at Wide Open Throttle (WOT) there is a difference of 5GPH but at 3000RPMs there is a difference of only 1.5GPH.

You will rarely ever use WOT, so let's assume you use a little more than mid range  and use 2.0GPH for comparison.

Now let's assume you use your boat 100 hours a year and the marina charges you $4/gallon

The cost of fuel difference is $800/year extra on the 350 vs the 4.3.

I've seen this engine (4.3MPI) in the slightly smaller, lighter Hurricanes such as SS 201 I/O and it performed admirably.  Ran well with a full load of people and kids on a tube.

If you plan to load your boat to capacity and do some serious watersports at the same time and every time, then consider the larger engine.

If you plan to take the family and cruise the lake, pull them on a tube, etc, then the smaller motor is more than adequate.

Ultimately you have to factor it all in. You'll have to compare your true current needs, future needs, upfront costs, plus the ongoing operational costs of owner either engine.

My last comment, that I believe is the most telling, the OB version of this boat has a max rating of 225HP.  Makes you think the 4.3 MPI just might be the right engine

I hope this information is helpful.

 

cjjjdeck

nquirk has the engine comparison right on the money!

Just curious, are you dismissing the 5.0L MPI Catalyst (@260 hp) in your consideration (or maybe you just wanted to get an opinion on the extreme ends knowing there's a mid-choice) ?  The 5.0L is the same engine block as the 350 Mag with a shorter stroke, frankly, both are excellent engines (4.3L is too).  The general rule of thumb on speed vs. horsepower once you get up in the ranges of these powertrains is approx. 1 MPH per 15 HP (of course there are other factors that can affect speed).  So the difference in speed I would have gotten from paying for the engine upgrade (5.0L to the 350 Mag) would have yielded me about 2 to 3 mph more, 

One serious consideration I would recommend is taking a closer look at the Bravo 3 drive.  The performance benefits of that drive is felt at pretty much any speed and with any engine.  The boat you're considering is not much lighter than the SD237 I/O, which I have (now discontinued).  The money I would have spent on the higher horsepower engine (350 Mag) I decided to spend on upgrading my drive and I couldn't be happier with the decision.  The Bravo 3 gives better maneuvering at high speed, but even more so at low speed (trolling and more importantly, docking). Other advantages are quicker on plane speed/hole shots (benefits some water toys), lower planing speed (lower RPM's which adds to fuel efficiency), less bow rise on acceleration (although the flatter bottom helps with this as well).  I also have not had the need to add trim tabs as some of the outboard owners have done to aid in the performance of their boats.

Just some food for thought.

RSTAC1

Thank you for the feedback and especially the links!  This really helps in making decisions.  Thanks again!