After what’s been described as the single biggest investment in Mercury Marine’s history, the American outboard manufacturer has just released its first ever range of V8 outboards. Story by Lawrence Schaffler.

The new V8s – some five years in development – come in 250hp and 300hp versions. Sleek in their white (or traditional black) livery with snazzy, coloured accents down the back of the cowling, the engines are super-slim, super-quiet and super-torquey.
Naturally-aspirated, they need plenty of displacement to develop their power and torque, and both models are built around a 4.6-litre powerhead. As ‘quad-cam’ engines, each bank of cylinders has separate intake and outlet camshafts, making four in total, and these articulate 32 valves, four per cylinder.

They’re also impressively versatile. Thanks to some smart engineering tweaks, the same, basic V8 comes in a range of variants to suit different applications and markets across the recreational, performance, commercial and racing sectors.
They carry many of the features introduced with Mercury’s new range of V6 engines, launched at the Miami International Boat Show earlier this year. Also naturally-aspirated, the V6s are available in 175, 200 and 225hp versions using a 3.4-litre powerplant with 24 valves. And like the new big sister, the V6 is offered in a range of variants to suit different applications.
So the V8 is a logical extension of the V6.
But where the V6’s geometry enjoys a natural ‘synchronicity’ and ‘balance’ with six cylinders firing at 60-degree intervals, the V8s are equipped with a balance shaft to reduce vibration and keep things spinning smoothly.
The global launch of the V8s was in mid-May, but boating journos Down Under were given a sneak preview a month earlier in Australia. The engines were mounted on a variety of boats, in single- and twin-rig configurations.
They are magical, powerful beasts in all sorts of ways – but my over-riding impression? Smoothness and quietness. Petrol-heads might see ‘V8’ as an abbreviation for ‘deranged, testosterone-boosting grunt’. Perhaps – but I think ‘dignified’ is a better description for these engines. Even the twin 300hp rig. More about this in a moment.
If you’re going to spend five years – and who knows how many dollars – developing a new range of engines, I guess it’s logical that much of the R&D will be channeled into market-differentiating features. And like the V6s, these new V8s bristle with them. There are way too many to cover here, so I’ll home in on what I think are the most significant: Idle charge management = peppier batteries – smart communication between the alternator and batteries sees the latter given a boost when you’re trolling. Sensors detect that the engine idling at 600rpm isn’t really helping the batteries – particularly if you’re running multiple MFDs, the stereo and your new 12-volt Espresso machine at the same time. So the revs are increased automatically to compensate.
Optimum fuel efficiency – as naturally-aspirated engines they are far more fuel-frugal than their super-charged siblings. But the V8’s Advanced Range Optimisation enhances this further. The engines are equipped with an array of oxygen sensors and, by talking to the engine’s ECM, ignition timing and fuel-air mixture is automatically adjusted to suit the conditions/load.
This automatic air/fuel mixture adjustment is best illustrated during hole-shot – when the boat transitions from rest-toplane. It’s a bit like hands-free dialing in your car, but you don’t have to talk to the engine.
Noise/vibration reduction – there are quite a few factors at play here. They include a new air intake design, fancy engine mounts which isolate the engine from the transom, and the aforementioned balance shaft. How they all combine is interesting but complex. But I assure you they run remarkably quietly and vibration-free.

Slim-line profile – it’s hard to believe there’s a V8 nestling under the cowl. The angle between the banks of cylinders is a mere 64o, making for a modest width. For owners keen on retrofitting a twin-rig (or triple), this has obvious benefits. Slimmer engines mean they can be separated by more width, and coupled with Mercury’s Joy-stick technology, that delivers superior maneuverability. Similarly, anyone keen to fit a triplerig has more space to play with.
Standard fuel – unlike many high-performance engines, the V8s run on conventional 91-octane rather than 98-octane fuel, and fire with standard spark plugs rather than the more expensive Iridium versions.
Service door – maybe not a big deal for owners who rely on the agent to service the engines, but you should – at the very least – be checking the oil level from time to time. This is a piece-of-cake with the pop-up service door built into the top of the cowl. And if the oil is low, the filler cap’s there as well. I also like the new cowl securing system. If you want to remove the cowl, that service door hides a single button. Depress it, a handle pops up, and you lift off the cowl. No more complicated, difficult-to-access clips.

With a little tweaking, the same, V8 powerplant has been configured for different applications and vessels – recreational, performance, commercial and racing.
The SeaPro V8, for example, is geared to the commercial market – where the boats are typically used for transport, Coastguard duty and commercial fishing. Compared to the others in the family, the SeaPro boasts a beefed-up gear case to handle the heavier workloads. The ProXS V8, by contrast, is geared to the racing fraternity and celebrates that fact with a racier gearcase – and a blood-stirring exhaust note.
And to optimise that versatility, owners have a choice of different steering systems – cable, hydraulic or digital throttle and gear-shift. So they’re easy to retrofit, using your existing linkages.
Developing 300hp, these V8s obviously have plenty of hold-onto-your-hat. I was most impressed with the twin 300hp rig. Fitted to a 7m fibreglass boat with seven adults aboard, they launched us on to the plane and to 50 knots without a hint of sweat – and there was plenty more in reserve. We had a prudent helmsman.
But their dominant characteristic, for me, was the lack of noise and amazing smoothness. Get a group of boating journos together on a single boat and there’s never a shortage of juvenile chatter and banter. I could hear all of it…

Sadly, I can’t provide any New Zealand pricing yet, but I think the V8s will be welcomed by Mercury fans – and perhaps attract a few converts. There, is of course, some bad news. Well, for die-hard two-stroke fans anyway. While the V8 debut marks the beginning of a new era for Mercury, it also signals the end of another. As of May 19 the company has ceased manufacturing its DFI two-stroke engines.