swapping 120 force for 115 4stroke? performance?

[Maxum21]

Hey guys, i have a 17' Bayliner with a '95 Merc Force 120. Ive come across a few good deals on a 2005 Suzuki 115 4stroke efi's. I've always wanted a 4 stroke but dont want to sacrifice performance. I'm curious as to how the 115 Suzuki would perform against the force. From what ive read from the past, the force hp is rated at the flywheel as oppsed to the prop. However the suz is 5 less hp and quite a bit heavier. Ive never ran a 4stroke and would like some insight. Basically, would i lose acceleration or top end by switching to the 4 stroke in this case?
thanks!

 

[JB]

Re: swapping 120 force for 115 4stroke? performance?

The torque curves are different. The Force would probably give a slightly better hole shot, but I doubt that you could tell without a stopwatch.

The performance of any combo depends a lot on the fine tuning of the propping and rigging. The Suzi would certainly be quieter and more economical and easier to find parts for. It is typical that, at idle, all you would hear is the tell tale splashing.

 

[Frank Acampora]

Re: swapping 120 force for 115 4stroke? performance?



Well, I'll tell you what: Normally I am a die-hard 2 stroke guy. I have a Suzy 30DF (four stroke) mounted on my 14 foot test boat and took it for a test ride before putting it up for sale on Craigslist. WOW! Was I surprised. That little 30, while heavier than a 2 stroke and smaller than any engine that was ever on the boat, did a surprising job. With two people in the boat weighing about 500 pounds, it ran at a respectable top speed--I don't remember exactly but I think it was about 27 on the speedometer not GPS. Still, respectable, and the acceleration was not doggy--that surprised me since I have always heard the because of less torque, four strokes usually have a poorer hole shot than two strokes..

It was quiet enough that at full throttle we could talk to each other and, of course, no fumes backing into the boat at idle.

All in all, a very good engine. NOW---If that translates over into the bigger engine, you very well might be happy with it.

Oh, yeah! we started the test run with only one gallon of gas. Obviously we didn't intend to run too long but as I remember, we were out for about 1/2 hour and did not run out of fuel.

Just so you can see: This is the boat on which we mounted the Suzy for testing.

 

[blackhawk180]

Re: swapping 120 force for 115 4stroke? performance?

I run a 115 four stroke on my 20' aluminum boat that is rated for 150 max. Bought it used and that's what it came with. I've got about 50 years of 2 stroke experience and this was my first 4 stroke (outboard) and to be honest, I was pretty underwhelmed at first. Hole shot was dismal. After finally getting the right prop, I'm happy with it but lost about 4 mph on the top end. If you do get the Shuzuki and don't like the hole shot, re-prop and go stainless. Made a huge difference for me.

 

[Maxum21]

Re: swapping 120 force for 115 4stroke? performance?

appreciate your thoughts guys. the thought of only hearing my tell tale splashing at idle is very appealing. Ive had plenty of 2 strokes in the past and i never really liked all the smoke and noise, however they ran STRONG.. i dont really mind if i lose a little hole shot, but i dont think i'd be happy losing 4mph on top end. as mentioned i can always play around with props, to an extent.. its just a tough descision. i'd love to test drive a similiar boat with a 115 four stroke to see how it performs, but it most likely wont be equivelant(diff hull/weight etc)..just out of curiousity do you how much hp a 120 force puts out at the prop? i mean if its rated for 120 at flywheel, would 100 hp at prop be a rough estimate? in that case i may not lose much performace going to a 115hp 4stroke rated at prop, correct? just rambling now

 

[Frank Acampora]

Re: swapping 120 force for 115 4stroke? performance?

The misconception is amazing to me: Since 1982 or 84 when the NMMA STANDARDIZED horsepower, ALL outboards are rated at the prop. The Force 120 puts 120 horsepower into the water at wide open throttle (if propped to run at rated RPM). The Suzuki 115 delivers 115 horsepower to the prop at wide open throttle. The difference is in how it gets to wide open and top speed. 115 HP is 115 HP, is 115 HP. As mentioned above by JB, hole shot may be a bit sluggish. However, If propped correctly the zuki should run almost as fast as the Force--5 Hp should not even make a 1 MPH difference.

NOW: Merc almost always under-rated their horsepower so a 120 Merc MAY be putting a good bit more than 120 into the water. I have seen a 4 cylinder 100 horsepower Merc outrun my 4 cylinder 140 Chrysler on the same boat. No way was that 100 putting out its rated horsepower! That is where the confusion arises.

AS a matter of interest, even if you take an early Force say 1989 and compare it to a late Force, say 1995. The late force with a Mercury lower unit and gear ratio and a Mercury water pump will usually outrun the earlier even though both are rated 120 at the prop. See: It is not only the horsepower at the prop, but the way you put it into the water that counts. Concrete example: Change the lower unit on an early Force from 1.73 ratio to a 2 to1 ratio and you will gain 3-8 MPH on the same boat with the same engine.

 

[briangcc]

Re: swapping 120 force for 115 4stroke? performance?

My Bayliner had a similar swap - 120HP Force to 115HP Honda. What a difference with the Honda! Couldn't tell it was running at idle. Very similar performance underway. Only thing I really noticed was that the boat sat a little lower in the water as it wasn't designed for the extra weight on the transom.

Loved the idea I wasn't pre-mixing 50:1, no more 2 stroke oil smell when under way, etc. You won't regret making the change.

 

[Maxum21]

Re: swapping 120 force for 115 4stroke? performance?

Brian, did you lose any top end mph? did you have any issues bolting up the honda? eg: did the bolt holes in the transom line up?

 

[briangcc]

Re: swapping 120 force for 115 4stroke? performance?

Top end - not that I really noticed. Bolt hole wise - the marina installed it, but I believe no new holes were drilled in the transom for the install. I remember checking the access hatch and I didn't see anything extra through the transom at that time. The controls needed to be changed as did the wiring. I believe the marina added a new trim gauge to mate up with the Honda - no biggie. Only other thing that comes to mind was that the new controls had the starter switch in them and that left the original Bayliner starter switch in the dash just to plug the hole. Had I held onto the boat, I would have put a decorative plate over that original Bayliner starter switch.

Not sure why but the marina that did the work left a lot of the old wiring in place, snipped at both ends. I just went through and pulled all the old wiring out that wasn't being used.


Nothing insurmountable by any stretch.

I do miss that '99 Bayliner of mine with that Honda on it. It was a heck of a lot lighter to tow around than my Four Winns. But I wouldn't downsize at this stage....I might add another though, which would land me right in the doghouse with the admiral.

 

[Maxum21]

Re: swapping 120 force for 115 4stroke? performance?

Brian, thats exactly what i like about outboard powered bayliners. Theyre light and easy to tow, economical to run, ecspecially if you have a 4 stroke hanging on the back. How do you like your current 5.0 i/o ? Four Winns are certainly nice boats!
I think i'm gonna go ahead and go with the Suzuki. I see no reaons why not to..The price is right and i can always sell my force to offsest some of the cost. It has a 2 yr old powerhead so it has to be worth something i guess..

 

[briangcc]

Re: swapping 120 force for 115 4stroke? performance?

I love the extra power and the added weight in the boat. The 50+mph top end is nice...now if I can just keep my wife OUT of the throttle so that I can enjoy my gas a little longer! I am having an intermittent issue since I had the marina change out the plugs. I think one of the plugs isn't seated properly, burnt, or one of the wires isn't quite on. I've yet to look at it as the boat is shrink wrapped. I'll have it checked out this spring when I have the marina summerize the boat and do the bellows - I'd try tackling it myself but I'll be in no shape to do so after knee surgery so I'll have the pros do it this time around.

It handles the rougher water better than the Bayliner did.

All in all, I love my Four Winns. I'm torn between another, the H210 that we looked at last year was VERY nice, and the Glastron GTS225. My problem is going to be finding a dealer that will sell one with the Volvo powerplant as my locals seem to be changing over to Merc only. I have a thing about Merc and I won't own one...that Force engine I had left a VERY bad taste in my mouth for Merc products. Calling that Force junk is insulting to Junk!!!

 

[briangcc]

Re: swapping 120 force for 115 4stroke? performance?

BTW: This is the best shot I have of it right now with the Honda outboard on it. I'll have to check to see if I have a side shot or something this weekend. I might, dunno.