Pontoon Boat & Deck Boat Forum

I was looking at my wife's 4cyl, 1.5L engine in her toyota yaris, when I was doing routine maintenance. As you can imagine, its quite a small engine. Its only 106 hp. But its great for us because its a 4 door sedan, and I measured 35mpg at the pump. That's city driving, on the highway it increases to 39mpg. And its a toyota, so if properly maintained, its going to be very reliable. Another japanese engine that'll go 450k miles.

So for what it is, its an awesome little engine. Why don't they put stuff like this in outboards, instead? Is it purely a fitment issue? I can see that being a problem, but I can also see a few solutions to that problem. I know a lot of boats do use inboard car engines, but I'm talking more along the lines of outboards here. IIRC, honda makes a 2.4L four banger that was 220 hp. Not bad for a 4 banger. I believe it was in one of their "R" model cars. And that new Mustang ecobost is a 310hp 4cyl.

So all that said, its not really all that big of a deal to make a 4cyl car engine, that would fit the needs of just about any outboard. Provided it would all fit. So why do they still use the sideways head design?

Simple, car engines are not designed to run WOT for long periods of time AND extra displacement is needed for decent torque (hole shot) in an outboard. A lot of Honda outboards use their car engines as a base design and some of the Suzuki engines are too. Same goes for Trucks, Ford's 5.0 is 420hp in the stang but tuned for more low end torque and longevity at 360hp in the F150

Also, a vehicle engine is horizontal while an outboard engine is vertical.

If you think about the oil "sump" you can imagine the problem with just turning the engine on it's end.

I've heard that the Honda 135 & 150hp outboards use essentially the same 4cyl as is in the European Accord. Mine sips fuel and is super smooth and extremely quiet. Honda car engines seem to last almost forever.

my v6 honda looks like it was pulled out of an minivan.

Well, years ago Homelite turned some auto engines on end and made the first 4-stroke outboards. And they didn't have any of today's technology

Boats rely on torque to get them on plane. Modern car engines are very short of torque, and they get their power with high rpm's and six speed automatic transmissions with very low gear ratios in the first 2 gears. But they're certainly not going to pull down a tree when you tie a rope to the bumper.

The old 4 cylinder 140 hp Mercruiser is 3.0 liters, about the same displacement as 300 hp 6 cylinder motors. It's a torque monster compared to newer 4 cylinders, but even it was a dog coming "out of the hole". But they ran okay when planed off and up at speed.

Interesting replies. Seems there are some problems with it, yet a couple of them have still done it. Like honda and suzuki. Maybe they're only doing it in the "sweet spot" where their 4 cyl car engines would actually work. And then they switch back to standard sideways head stuff for the larger engines.

I know 3 boat mechanics, all 3 hate working on honda and suzuki. maybe thats why

If the honda engines are anywhere near as reliable as their car engines, they shouldn't need worked on much. Probably people tearing them up though

i have two honda aquatrax (jet skis) they use a four stroke turbo charged engine i am told the engine block was based on the honda FIT car
the engine is horizontally mounted but has a dry sump design which allows the engine to run in any position.
it is a 1.2l that puts out 165 hp

Jet ski may use 165 HP for the hole shot but much less to maintain cruising speed just like a car. Bigger heavier pontoon boats usually don't accelerate well and are propped for maximum speed thus using all the HP at full throttle for long periods of time. Dragsters can get over 1000 hp out of each cylinder on a V8 but only run about 600 revolutions between rebuilds.