All the 350hp outboard engines compared

After a couple of years of slim pickings, anyone in the market for a new 350hp engine will soon have a wide range of choices to shop from.

Of note, three of them are still very box-fresh after launching in the last 12 months.

The differences between how the 350hp outboards engines produce their performance are quite large, so it's a good exercise to look at each engine's strengths and weaknesses before settling on the one that will be the best choice for your needs.

The biggest-displacement outboard engine in the 350hp class is Mercury’s V10 Verado.

Launched in Australia earlier this year and currently in high demand, Mercury’s new 350hp outboard engine follows the mantra of a big-displacement, normally aspirated block that produces plenty of low-down torque for getting a boat up on the plane quickly.

It had to, as the new outboard engine was engineered to replace a supercharged in-line six-cylinder powerplant that was as heavy as the engine that has replaced it, and complicated to maintain.

Mercury’s solution was to develop a narrow-bank 5.7-litre V10 that mimicked the supercharged engine’s performance but with fewer moving parts. It also had to perform at its peak on regular unleaded fuel.

The engine includes some unique features, including a lower leg with a much larger torpedo and one of the biggest propellers you’ll see on an engine that hangs off the transom, Mercury’s flagship 600hp V12 Verado excepted.

Despite its high cylinder count, the 350hp Mercury V10 Verado tips the scales at just 315kg, a big competitive advantage over similarly powered rivals competing for transom space. On a triple-engine install, this weight advantage can make as much difference as adding a fourth V10 Verado and still having kilos to spare.

Mercury makes its own engines, so the new V10 resembles nothing else out there. Rather than being a cut-down V12, the engine is more closely related to Mercury's V8 powerhead, and shares many of its parts from the drive leg up.

While the new V10 shares the same 35-inch width between mounting holes as the V8 meaning you can stack multiple engines just as tightly across the transom, the taller V10 has to mount an inch higher on the transom meaning a repower will need more than just pulling off the old engine and bolting the new one on.

One feature that's not on the 350hp Mercury V10 Verado is a telltale, the stream of water from the cooling system that gives a visual indication that cooling water is pumping through the block.

It also gave an audible signal that the engine was running but was dropped because this new engine runs so quietly at idle that it actually detracted from the experience. Instead, you'll be relying on your helm electronics to warn you if things start warming up too much.

For those times you don't want to be quiet, the 350hp Mercury V10 Verado also comes with a mode that bypasses the exhaust to give a deep, throaty V10 burble.

One of the big points of difference that the 350hp Mercury V10 Verado has over competitors is an alternator that will produce 90 amps at idle and 150 amps when running. This is to future-proof the engine for a new generation of 48-volt accessories such as bow thrusters and gyroscopic stabilisers that will one day replace the current 12-volt versions.

Mercury has also given a lot of attention to high-traffic servicing touchpoints, ensuring they're easily accessed and highly visible, and don't need you to remove the cowling to reach them.

As for pricing? Mercury hasn't shared that detail with us, but the previous-generation supercharged 2.6-litre in-line six-cylinder engine it replaces cost around $50,000, and we're told the V10 version will be more expensive.

When it launched in 2017, the Suzuki DF350A instantly became the flagship of the Japanese outboard engine maker's line-up.

The Japan-built engine is based on a 4.4-litre narrow bank V6 originally developed for the Suzuki DF300AP. 

Suzuki is the only outboard engine maker to equip its 350hp outboard engine with a drive system featuring two three-bladed props mounted in series, but turning in different directions.

The idea is that the extra surface area from the second prop helps the DF350A bite onto the water and transfer all its torque into forward momentum.

Performance comes from a 4.4-litre V6 running an exceptionally high 12.0:1 compression ratio that needed some extra engineering to avoid engine knock, where the fuel is burnt in the cylinder at an uneven rate.

Instead of using one injector per cylinder, Suzuki has engineered the DF350A with two per cylinder, allowing more precise control over fuel flow and more cooling air to mix with the fuel.

The engine’s pistons have also been re-engineered using a “shot pein” method that creates a dimpled surface, improving the way that fuel is burned in the cylinders. Suzuki has had to strengthen the engine’s conrods to handle the extra performance.

Suzuki’s design for other DF350A also stands out from the crowd. The top cowling is built around a double louvre at the air intake that is designed to remove water from the air. This also gives the engine its contemporary "hooded" look.

Of note, the engine includes a lower water pick-up as well as the standard one located on the drive leg. The lower pick-up allows the DF350A to operate in shallower water than competitors – a key feature developed for US owners. 

Suzuki’s DF350A has an expensive taste in fuel, preferring premium unleaded over regular.

Suzuki is the only manufacturer to list a price on its website that gives you an idea of how much a new engine is likely to cost. For the DF350A, it's $46,750 before rigging costs are factored in, with the forward controls adding up to $5300 to the price tag.

Honda late last year launched its first-ever production V8 as a platform for the most powerful outboard engine it has built, the all-new BF350. It is yet to arrive in Australia.

The engine is built on a 5.0-litre narrow-bank block that taps into Honda's VTEC (Variable Timing and Lift Electronic Control) system that changes the camshaft profile and valve lift to either produce more power or eke out maximum fuel savings.

According to Honda, its new BF350 “offers impressively low noise and vibration, whilst delivering a new distinctive, rich sound and exhilarating performance, with every feature designed to enhance the boating experience”.

Honda's new engine, which should launch in Australia mid-way through this year, comes with fly-by-wire controls that allow skippers to use a single throttle lever to manage multiple engines at the push of a button.

The new engine will also launch with a new multifunction touchscreen to allow the skipper to monitor its operation in real time.

Of note, the new Honda BF350 gains cruise control based on the trolling function, allowing skippers to adjust the boat’s cruising speed via the engine’s control head. It means the skipper can set the revs from the BF350's 650rpm idle right up to the 6000rpm redline. The trolling function will still operate between 650-1000rpm in 50rpm increments.

The engine also adopts an automatic tilt-stop system that will automatically tilt the BF350 up to stop at a pre-determined angle. This is important for boats with smaller engine wells where fully tilting up the engine could damage the boat or the engine’s cowling.

So far, the BF350 is the only engine that Honda has launched off the new V8 platform. We'd expect that it will one day expand to a family of engines, with a 400hp the most likely next step.

After several years in the wilderness, Yamaha has launched an all-new F350, the 350hp Yamaha V6 Offshore, to plug an important gap in its product lineup.

The new engine has shaken off its former 5.2-litre V8 origins to tap into the V6 Offshore line-up with a new 4.3-litre version of the 4.2-litre bent-six range that caps out at 300hp.

It's not just a bored-out version of the smaller engine, either. The new 4.3-litre V6 has several enhancements that improve its performance including using iridium spark plugs that are better suited to performance engines compared with conventional plugs.

The new V6 runs a 11.1 compression ratio to extract more performance. Weight is 250kg for the lightest version, the same as the Yamaha F300 on which this engine is based and, we should note, the lightest in this class by some margin.

The extra engine capacity is gained by increasing the block's stroke by an extra 2.0mm to make it slightly undersquare.

The new Yamaha F350 is fully electronic, with electric steering integrated into the mounting bracket and a fly-by-wire throttle and shift control. That makes it fully compatible with Yamaha's Helm Master EX joystick control system, the only one on the market that has adapted to control a single engine.

The F350's peak performance comes at 6000rpm. To help improve grip on the water at low speeds, Yamaha has developed the F350 to divert its exhaust away from the propeller when the engine is in reverse and turning at less than 2500rpm. This markedly improves the engine's ability to back up.