Of course now there are diesel outboards. I've decided I'm not a diesel guy, if I had a Nordhaven and crossed oceans I'd definitely be a diesel guy. I love outboards until you have to add a dinghy to boats 32 feet and under, then swim platform I/O all the way.
Thought I'd copy and paste an older article talking about the new Merc engines used for I/O boats and what has changed ( a lot). Much of the criticism has gone. For example, my old Merc V8 vented through two vent holes in the transom. Those holes are now going to be used as drains for my new scuppers. So the new motor exhausts through the leg so there goes the stinky and noisy critique. Read the article, you will see many changes to make the engines suitable and solely designed for a marine environment, even salt water:
"The Latest Technology In Sterndrives [all the engines discussed in the article now exist]
By Michael Vatalaro
For decades, gas inboards were big, simple, marinized automotive blocks. But now the technology is at a crossroads of sorts, and it's anything but simple.
A new generation of sterndrives are quieter, stronger, and more fuel efficient.
The inboards on my last boat were based on a V-8 design from 40 years ago, popular, I was told, in taxicab fleets. Robust to be sure, but they were also noisy, smelly, and reliant on the vagaries of the four-barrel carburetors that sat atop each block like carbon-smudged crowns. It may be a cliché, but one of the first things you notice while being around modern inboards is, well, they start. As in the first time you turn the key, just like your car. And that's no accident, considering there are very few differences between the engine powering today's boats and the one in your light truck.
Our marine inboards have always shared a basic design with automotive engines. But until recently, the biggest inboard manufacturers, Mercury Marine and Volvo Penta, relied on blocks from General Motors that were a generation or two behind the times. That's all changed now. In a major departure from the status quo, Mercury announced in June 2014 that it would produce a block of its own design for the MerCruiser engines. Volvo went in the other direction, and it began basing its designs on newer-generation GM blocks. These two different approaches to the same problem — how to improve the boating experience for those of us with gas inboards — can be boiled down to opposing beliefs.
"Six years ago, GM notified us it was discontinuing manufacturing the blocks that we'd used as the basis of our engines for the past 20 years," says Marcia Kull, vice president of sales for Volvo Penta North America. "At that time, we needed to make a decision. We asked ourselves, are engines more like a basic commodity, or are they an important component that influences the boating experience?" Volvo Penta believes that all the engineering work and technology built into those GM power plants pay dividends to boaters in measurable ways, so the company moved forward using the very latest GM Gen 5 blocks.
Mercury, on the other hand, surveyed its options, then chose a different direction.
"Most of what's happening in automotive is introducing a level of tech that's very good for an automotive application but delivers little benefit to marine purposes," says Facundo Onni, director for product management at Mercury Marine. "Given the marine-duty cycles that require higher rpm and high torque at all times, the automotive fuel-efficiency focus adds complexity and cost without much upside." Mercury believes starting with a blank slate — designing a new marine power plant from scratch — provides advantages that can't be achieved with the GM block. As consumers, we now have a real choice between inboards, and here's why that's a good thing.
Same Power, Fewer Cylinders
Both builders have rolled out new V-6 engines with horsepower ranging from 200 to 250, the sweet spot for sterndrive power formerly occupied by small-block V-8s. These power-dense engines are truly remarkable in that they're putting out nearly identical power to their bigger, older cousins while using less fuel and creating fewer emissions — and they weigh less. In the case of Mercury's 4.5-liter V-6, with its newly designed block, the 130-pound weight savings over the old 5.0-liter V-8 comes at a cost of only 10 horsepower, noticeable only when the throttle is wide open; the V-6's impressive fuel savings run around 15 percent.
Both Volvo and Mercury have made servicing these engines easier. On the Volvo, the company not only located all the service points on the front of the block, where you typically have the best access, but also designed these parts to be common to all the inboards in its lineup, V-6s and V-8s alike. This means your mechanic will be very familiar with servicing your motor, no matter which model it is. For the do-it-yourselfers, easy access means you're less likely to put off a maintenance task simply because it's inconvenient.
On the performance side, the variable valve timing and wideband oxygen sensors in the Volvo engines allow it to start and run well in all conditions while using a variety of fuel qualities. A higher rpm range (6,000 is the max for the V-6 models) is more like that of an outboard, and this gives boat builders greater flexibility in propping their boats for best performance.
The new Mercury block has zero GM parts.
"We like the new-generation automotive blocks," says Kull. "They're just stronger, more powerful engines. Boats are getting the same performance out of smaller, lower horsepower blocks. The boater isn’t paying more for larger engines up front, or paying to feed those big engines all the time," she continues. "There is a replacement for displacement."
Starting from a blank slate, Mercury focused on ease of maintenance and making the engine smooth and quiet. For example, a lightweight flywheel makes for smoother shifting. Mercury also moved the throttle body, and all the noise associated with it, to the back of the block. The throttle body usually faces forward on an automotive engine, away from the driver of a car. But on a boat, that points the throttle body right into the cockpit. Mercury says the change reduces engine noise by 3 decibels. In addition, the plastic cowling material on top of the engine cuts down on high-frequency noise, making the engine less harsh to the ear. Even the oil pan has noise-deadening properties. Mercury even decided that the fuel-pump noise was irritating, so it changed that as well. All of these refinements add up to a quieter, more pleasant engine to be around.
Mercury also makes owning one of its engines easier with one-touch drainage of the (raw) water portion of the cooling system. Turn a knob, and all the water drains from the block, making winterizing a snap. "We call that the season extender," says Onni.
New Perks
There's a lot to like about both of these new blocks. Digital engine control means a boat powered by either brand won't bleed speed while turning or require input from the helm to keep a steady speed.
It's easier to breathe near both of these new designs, too. While all new inboards are required to have catalytic converters to transform hydrocarbons (unburned fuel) and carbon monoxide in the exhaust to less harmful water vapor and carbon dioxide, it's hard to overstate what a big change this is from just five years ago. For example, Volvo says that its new engine at idle emits 95 percent less carbon monoxide than previous designs.
Bigger, Better
For those of us brought up on engines with carbs and distributor caps, lifting the engine hatch and seeing the smooth plastic cover of one of these modern blocks may be a bit of a surprise. But as soon as you turn the key and push the throttles forward, the improved performance over their forebears should begin to wow you."