When you buy a car it come with an engine, leaving you little to think about other than the color of the paint and the best place to hang your fuzzy dice, but when it comes to buying outboard engines we have the luxury of choice. Not just between manufacturers, but also between weights, outputs, and even methods of power generation. And that’s to say nothing of the re-power market, where an engine can be fitted to a bare boat or used as an upgrade for an existing unit.

outboard engines honda

With a huge array of options, it can be hard to know where to start - especially when buying an outboard engine for the first time.

In the past, picking an outboard tended to be a fairly simple choice between two- and four-stroke. On the one hand you had the lightweight simplicity of two-strokes, with their excellent hole-shot and vigorous throttle response - and on the other, you had the cleaner, more refined four-stroke engines. But the need to comply with environmental standards (and the modern customer’s wish to pick the cleanest and most efficient option) has seen the choice of outboards expand enormously, with four-strokes now available from two to 350 hp, Direct Injection two-strokes across a slightly less extreme power spectrum, and an ever-expanding range of squeaky-clean electric options.

Direct Injection two-strokes

The latest Direct Injection (DI) two-stroke outboards employ sophisticated engine management systems to produce a combination of performance, economy, and refinement radically removed from their simplistic two-stroke predecessors. Most of this is achieved by improving the method by which fuel is introduced into the cylinders.

These new DI outboards (primarily from Evinrude, Mercury, Tohatsu, and Yamaha) shoot a very precise

Modern direct-injection two-stroke outboard engines.

amount of fuel into the combustion chamber at exactly the right time. This replaces the more approximate methodology of the carburetor and not only does it mean that the fuel is better atomized, but it also results in a cleaner, more complete burn, with no fuel wafting into the chamber and inadvertently spilling from the exhaust port.

As regards lubrication, a precisely metered stream of oil lubricates the rings and bearings before flashing off in the combustion chamber. This oil then exits along with the exhaust gas, but the proportion of oil burned is minuscule and its impact on emissions is minimal. In short, a modern DI two-stroke offers plenty of the traditional low-end torque we all love, while bringing cleanliness into line not just with modern environmental sensibilities but also with modern fuel prices.

Big strides for four-strokes

For most leisure boaters, however, four-stroke outboards remain the number one choice - and the biggest players in the modern marketplace are Honda, Mercury, Suzuki, and Yamaha. Most use a fuel-injection system developed from the sophisticated multi-port technology of the automotive industry, with one injector per cylinder generating crisp throttle response and vast improvements in economy.

four stroke suzuki outboard engine

A modern four-stroke outboard, from Suzuki Marine.

However, as four-strokes only produce power on every other up-and-down movement of the crankshaft, they have tended in the past to lose out to two-strokes on low-end performance. To compensate for that, many manufacturers now incorporate a lower gear ratio, thereby increasing torque and closing the gap in ‘hole-shot’ performance. Others have developed exhaust back-pressure reduction systems, increased throttle valve sizes, and use more displacement to meet this goal.

On the water, this means that those of us who lamented the end of the traditional two-stroke can cheer up, because with the modern four-stroke, you get pretty much all the performance benefits plus astonishing levels of refinement. The continual reduction in physical size and weight also means a broader range of power outputs are available for small boat transoms - and at the other end of the scale, some truly epic 350 hp engines, including the supercharged Mercury Verado and the monstrous Yamaha F350, mean that far larger boats can now consider outboard power as a real option.

What about the small stuff?

For small boats, there are certainly lots of old two-strokes on the used market. But if you want a shiny new internal combustion outboard, your only option is four-stroke - and they are astonishingly frugal. A two or three horsepower unit on a well-matched runabout could easily provide a full day’s entertainment for a gallon or two of fuel. Of course, it’s more expensive to buy new (from around $800 for a new 2.5 hp four-stroke) but other than a lower purchase price and a simpler maintenance program, the older style two-strokes now offer no practical benefits over these modern engines except for lower weight.

So what about an even newer technology, namely, electric outboards?

torqeedo electric outboard motor

Electric outboards, like those from Torqeedo, are another option.

They are well suited to small boats and inland fishing, with easy portability, silent propulsion and cheap running costs. The batteries are likely to need replacing every three years or so, but that’s offset by the fact that you don’t need to buy any fuel. With prices from around $100 to more than $5,000 from names that include Motorguide, Minn Kota, and Torqeedo, electric outboards go from simple trolling motors to remotely operated units that can power sizeable boats. They’re very compact and lightweight, and because a full overnight charge runs just a dollar or two on your electric bill, the running costs are fantastically affordable. In short, if you own a small boat, the modern breed of clean, reliable, low-maintenance electric outboards should not be overlooked. For more on these see Lenny Rudow's feature Solar Power for boats.

Ten key outboard Tips:
(1) Consider the engine weight as well as its output.
(2) Think about security, as thefts of outboards are all too common.
(3) Take advice from the boat builder about the best options for your craft.
(4) If possible, test drive a couple of different engine options on the same boat.
(5) If you can’t afford a new engine, think about reworking/upgrading your prop.
(6) If you’re a watersports fan, consider investing in some additional grunt.
(7) If you do most of your boating inland, make sure you explore the electric options.
(8) Consider the ‘peripherals’ (data displays, security features and service back-up).
(9) Price is obviously important but also consider the likely long-term running costs.
(10) Don’t discount the used market, as there are some very big savings to be made.

These are exciting times for outboard buyers, with rapidly developing technologies reducing weights and increasing efficiency, not just with internal combustion but also with electric propulsion. It is true that the price of a new outboard often exceeds the value of the boat to which it is fitted, but if outright speed is not your sole mission, then there are a great many ways to give your boat a fresh lease on life with some affordable new power.

Major outboard manufacturers

Alex Smith is an ex-British Naval officer, with extensive experience as a marine journalist, boat tester and magazine editor. He lives and works as a specialist marine writer and photographer from his narrowboat in Bath, UK.