N o, I’m not talking about
Thunder Over the Transom
No, I’m not talking about the thunder accompanied by lightning strikes and storm fronts—I’m talking about the thunder of hundreds of horsepower, more than ever before found under a single outboard engine cowl.
I’m talking about powerheads that create 300, 400, even 600-plus horses, by harnessing the energy released as gasoline and oxygen combine and ignite in up to 400 explosions per second. I’m talking about taming this violent chemical reaction to spin a finely-fashioned chunk of metal 6,000 times in the space of a minute, transferring those revolutions into thrust via a transmission and propeller which drive your boat through the water with neck-snapping acceleration and eye-watering top speeds.
Since Yamaha made the big jump over the 250 hp threshold in 2007 with the introduction of its F350—the first production eight-cylinder outboard and still one of only two on the market today—all of the major outboard engine manufacturers have taken a similar leap. Evinrude offers up to 300 hp, Mercury offers up to 350 hp and Mercury Racing up to 400 hp, and newcomer Seven Marine offers a mind-boggling 627 hp. Each of these manufacturers, however, has taken a very different technical path to create such power. And each path has its own up-sides and down-sides.
Yamaha started this latest arms race, so let’s look at that beastly F350 first. In its current iteration as the F350C the basics remain the same as they were when this engine was first introduced. It’s a naturally-aspirated four-stroke 5.3 liter V-8 with a 3.70-inch bore and a 3.78-inch stroke, EFI fuel induction, and dual overhead cams.
What exactly do all those specifications mean in layman’s terms? The engine makes its horsepower with sheer size and displacement, not high-tech tweaks and add-ons. This keeps the pieces and parts relatively simple, without over-stressing the engine or asking it to do more than it was originally designed to do. In the world of outboards the F350C is a tank, and no one would ever accuse Yamaha of under-building it.
The net result is demonstrated in a five-year warranty, and a well-deserved reputation for reliability that’s been earned despite a harmonic issue that takes place between 3,500 and 4,200 rpm on the F350C. It can cause flywheel damage over time, which Yamaha addressed by giving the engine an ECU that keeps tabs on engine rpm and determines when and if the flywheel should be replaced (which Yamaha does at no charge).
A down-side, however, lies in the engine’s weight and size. At 763 pounds this is one of the heaviest options around, despite the fact that Yamaha has managed to shave 41 pounds off of the motor since its introduction. On the transom of some relatively small center consoles, it looks ridiculously large.
The same can be said of Seven Marine 627, which dwarfs the competition in both horsepower rating and size. The 627 has a gigantic alien-looking cowl and weighs in at a whopping 1,094 pounds. That eliminates it as an option on virtually all boats under 26 feet, and many boats that are significantly larger.
The 6.2 liter V-8 is straight out of a Cadillac, based on GM’s LSA Gen 4 engine—which is a bit ironic considering that at around $90,000, the outboard engine costs more than an entire Cadillac CTS-V with the same powerhead under its hood.
The additional 0.9 liters of displacement doesn’t account for this engine having so much more power than Yamaha’s V-8. Credit for that goes to an Eaton crankshaft-driven, four-lobe rotor supercharger that crams air into the engine’s combustion chambers. The engine also has a cast-aluminum block with cast-iron cylinder liners and rotocast cylinder heads.
Again, let’s unpack some of this jargon to determine what it all means to boaters. First off, note that time has proved the design is solid. Cadillac’s experience has shown that utilizing the latest engine-building technologies (like rotocasting those cylinder heads, which eliminates porosity to deliver a stronger part) works wonders.
Don’t forget that land use and marine use are exceptionally different. Aluminum blocks don’t have a particularly impressive history in marine applications. Superchargers add another layer of complexity and more parts potentially fail.
The 627 simply hasn’t been around long enough for us to assess its reliability (the first model was unveiled last February at the 2016 Miami International Boat Show). However, Seven Marine’s rather convoluted, exclusion-riddled three-year warranty doesn’t instill a ton of confidence. On the other hand, if you simply want the biggest, baddest, most powerful outboard engine on the face of planet Earth, this is it.
Mercury and Mercury Racing also utilizes supercharges to make their outrageously potent powerplants, in the form of the Verado 350 and the Verado 400R. Both are based on a six-cylinder 2.6-liter four-stroke powerhead. Wait a sec—2.6 liters? That’s less than half the displacement of the F350C. As a result the Verados are more than 80 pounds lighter than the Yamaha and they take up a lot less space at the transom.
There are, however, a lot of caveats to consider. As we mentioned earlier, depending on a supercharger means more complexity, more pieces—parts that can potentially fail—and more stress on the engine as a whole.
Taking the Verado from 300 to 350 horses required water-jacketing the supercharger and hiking its boost pressure (which already doubled atmospheric pressure) by an additional six percent. These Verados also need to burn 91 octane fuel to attain peak performance, and require a minimum 87 octane.
Meanwhile, the 400R gets its extra oomph by simply spinning faster—top end RPM on this outboard is an industry-high 6,400 to 7,000 RPM. The 350 spins at a maximum of 5,800 to 6,400 RPM. Since both engines are less than two years old, it’s too early to tell whether Mercury has crossed any red lines here, but they’ve certainly moved the redline.
Again, the warranty provided with these engines offers some insight: you get three years on the Verado 350, and just two years on the 400R.
The only two-stroke outboard in contention is the Evinrude E-TEC G2, which maxes out at 300 horses. This direct-injection engine has a healthy 3.4 liters of displacement with a 3.85-inch bore and a 3.00-inch stroke, spins at up to 6,000 RPM, and tips the scales at a svelte 537 pounds, making it the lightest of these heavyweights by a long shot.
It’s also the least mature. Unlike the tried-and-true Yamaha, the Cadillac-converted Seven Marine, and the uber-tweaked Verados, the G2 is a completely fresh design introduced just two years ago.
Like all two-strokes built to date, it suffers from increased sound and vibration levels as compared to a four-stroke, but it also shows some serious cutting edge innovation and improvements.
Computational fluid dynamic software analysis was used to simulate fuel and airflow in the combustion chamber, which led to redesigned transfer and exhaust ports, pistons, and cylinder heads, as well as shifting the exhaust manifold for the port bank off to one side, instead of being centered along the back of the engine.
Techno-jargon aside, what this boils down to is rather shocking efficiency. For years we’ve all been told over and over again that four-strokes have better fuel economy, but hands-on experience with the G2 300 blows that assertion right out of the water.
I’ve now tested about a dozen on different boats. Without fail they post fuel economy numbers 10- to 15-percent higher than their four-stroke competitors.
Added bonus: two-strokes have fewer pieces (parts) and as a general rule of thumb, their relative simplicity translates into better reliability. The G2 hasn’t been around long enough to make any objective assessment in this regard, but Evinrude does claim the engine can go five years or 500 hours with zero scheduled maintenance—and they back it up with a healthy five-year warranty.
With all of these contenders, you have the ability to harness more horses than ever before. Modern technology and our hunger for power means it’s time to tell your passengers to hang on tight—there’s a storm brewing, and it’s right on your transom.
Outboard engines are incredibly reliable these days, but they’re still subject to many of the same old fuel problems we’ve always had to deal with. If your engine is cranking but just won’t start and you suspect it may be a fuel issue, remember these quick-fix tips.
Inspect the ball in your fuel line, which can indicate a number of problems. If it’s easy to pump and doesn’t grow firm as you squeeze it, there’s a good chance your fuel line has a leak and air is getting in and/or fuel is getting out. When the fuel line is properly sealed, the ball grows firm after a few pressure-building pumps. If, on the other hand, the ball is so firm you can’t pump it, that tells you that fuel isn’t moving through the system. This could be due to blockage, air-lock (inspect the fuel tank’s vent and make sure it’s open), or a faulty connection between the fuel line and the tank or the fuel line and the engine.
If you’re sure fuel is getting to the engine, your next suspect is the fuel filter. It’s rare that an external canister filter gets so clogged that fuel won’t move through it, but many outboards have small (read: easily clogged) filters inside the cowl. Since these are out of sight they often are out of mind, and few boaters remember to regularly clean them.
If you’re sure fuel is flowing properly but the engine won’t fire or starts then quickly shuts down, you may have water in your fuel or an ethanol issue. In either case, there’s only one way to find out for sure: disconnect the fuel line at the tank, and bring a different tank of fresh fuel aboard. Then try to start the engine on the new supply. If everything runs right, you’ll have to drain the boat’s tank and fill it with fresh stuff.
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