2-stroke versus 4-stroke - Soundings Online

2-stroke versus 4-stroke

Publish date:

If you plan to buy a new outboard in the next couple years, odds are you’ll be deciding between a direct injection 2-stroke and a 4-stroke. But which engine is right for you?

Comparing fuel efficiency is a good starting point. The first thing to keep in mind is that both 4-stroke and direct injection 2-stroke outboards on average are more than 35 percent better than traditional carbureted 2-strokes on fuel consumption, according to Tom Mielke, outboard marketing director for Mercury Marine. That percentage is based on how an average boater would use an outboard, he says.

It is a bit less clear whether a 4-stroke or a direct injection 2-stroke is more fuel efficient. Mielke says Mercury has found that for a given horsepower the new technology

2-strokes are more fuel efficient than 4-strokes when run at or just above idle, and again above three-quarter throttle, because the fuel is being monitored so precisely. The two engine types consume about the same amount of fuel in the middle of the rpm range, he says.

David Grigsby, marine group product manager for Yamaha, says the two engine types generally burn fuel at equal rates at idle and again at wide open throttle. However, the

4-stroke has a distinct fuel economy advantage at middle rpm (2,500 rpm to 5,000 rpm), he says.

Though they disagree somewhat on efficiency, Mielke and Grigsby both say variables such as engine block displacement and boat size affect fuel economy, and in some cases the general patterns don’t hold true. They also note the obvious: Both engine types will burn a lot of fuel at wide open throttle, and that boaters can find a fuel burn “sweet spot” by backing off a bit and watching fuel consumption.

Jeff Kalibat, owner of Yamaha dealer K&K Outboard in Island Park, N.Y., says a good rule of thumb is if you spend a lot of time above three-quarter throttle, get a 2-stroke, but if you spend most of your time below that mark, opt for a 4-stroke.

Operating noise also has improved with the new technology outboards, though it’s generally accepted that the smooth-running 4-stroke is superior to the direct injection 2-stroke in this area. Offshore anglers can run 4-stroke outboards at 1,500 rpm all day and hear themselves talk, says Robin Senger, “The Outboard Professor” and director of marketing for Honda Marine, which builds 4-strokes from 2 hp to 225 hp. The closest rival on the 2-stroke side may be the Evinrude E-TEC 2-stroke outboards from BRP — formerly Bombardier Recreational Products — which are said to run as quietly as a 4-stroke.

In addition to quiet operation, BRP says E-TEC engines release less soot and particulate matter than 4-strokes, and emit lower carbon monoxide levels, an emission component not currently regulated with marine engines in the United States.

Two-stroke oil is formulated for lubrication and combustion. The combusted oil of a 2-stroke is accounted for in its emissions, a factor in their old reputation for being somewhat smoky. A 4-stroke’s oil — which must be changed periodically — is for lubrication but not combustion, so the outboard produces less smoke. And keeping oil out of the combustion process results in longer spark plug life in 4-strokes, says Honda’s Senger. “We don’t even check the spark plugs until 400 hours,” he says. But, he says, direct injection engines are getting better and using less oil.

At the same time, the disparity between 2- and 4-stroke performance is closing. A former offshore powerboat racing world champion, Kalibat, for one, agrees, though he says it depends on the particular engine. He says a 200-hp Yamaha 4-stroke isn’t as responsive as a 200-hp high pressure direct injection Yamaha 2-stroke, but the new F150 4-stroke will stay right with a 150-hp HPDI. And he says he sees this as a trend. “As time goes on they’re able to improve 4-strokes to perform more like 2-strokes,” Kalibat says.

A 2-stroke engine accelerates better than a 4-stroke because it has a broader power band or range due to its better “breathing,” or how efficiently it draws air in and pushes it out. A naturally aspirated 4-stroke cannot be tuned to provide the same performance at as broad an rpm band as the 2-stroke. Also, a certain amount of potential output is consumed operating a 4-stroke’s valve train.

“You hit the gas and [the direct injection 2-stroke] gets up and goes. There’s not that lag time,” says Jim Morgenthaler, general manager of Tohatsu America, which builds 2- and 4-stroke outboards.

To deal with the breathing issue, 4-stroke manufacturers are using tuned intake runners and variable valve timing to improve the power band, and in some cases applying superchargers to perform more like a 2-stroke. Mercury, for example, last year introduced its Verado line of supercharged 4-strokes.

Though these solutions add weight to a 4-stroke, it hasn’t seemed to diminish their appeal. “Four-strokes seem to be what the customers want and [what] the customers need in most cases, as long as the boat can handle the weight,” says Kalibat, who does a lot of repower work.

In general, a 4-stroke is heavier than a 2-stroke, but that’s changing, too. In fact, Honda’s 50-hp 4-stroke is lighter than some conventional carbureted 2-strokes, and the 2- and 4-stroke Yamaha 150-hp engines weigh roughly the same. One way manufacturers are reducing 4-stroke weight is on the cranks and midsections, Senger says.

Suzuki uses hollow camshafts and plastic exhaust manifolds in its 4-stroke outboards, says David Greenwood, senior product development engineer for American Suzuki Motor Corp. Many of these new parts used in Suzuki outboards perform at 14,000 rpm on the company’s motorcycles, he adds.

“We’re always looking for ways to shave a few pounds here and there,” says Tohatsu’s Morgenthaler. “But an inherent part of 4-strokes [is] there are more parts. There’s no way around it.”

Mercury’s 2-stroke direct injection OptiMax 225 weighs 497 pounds, and BRP’s V-6 E-TEC 225-hp 2-stroke weighs 516 pounds. Comparable Mercury and Yamaha 4-strokes weigh 583 pounds, Honda’s BF225 4-stroke weighs 599 pounds, and the Mercury Verado 225 weighs in at 649 pounds.

Boatbuilders are modifying hulls to accommodate heavier engines, and some companies, such as North Carolina builder Southport Boatworks, are designing models expressly for use with 4-stroke power. And Zodiac has introduced a line of dinghies for use with 4-stroke outboards. “Until now it’s been a real problem in small dinghies,” says JJ. Marie, Zodiac of North America president and CEO. He says the additional engine weight kept some small boats from getting on plane.

While more boats will be able to handle 4-strokes in the future, does that make the outboards the right choice? Brett Shields, owner of Shields Marina in Saint Marks, Fla., says a lot of boaters are under the mistaken impression that they will be outlawed from using 2-strokes in the future, or that 4-strokes are more durable. Shields says he has a customer with 6,000 hours on an old-style 2-stroke, and that advances with metals on the Evinrude E-TEC could equate to much longer engine life.

“No break-in is required [with E-TEC],” says Shields, who is a dealer for Yamaha, Honda, Evinrude and Johnson outboards. “That tells you there’s not going to be a lot of wear and tear.” However, Shields notes that the technology hasn’t been around long enough to see if this is the case. E-TEC engines won’t need scheduled maintenance for a warranty period of three years or 300 hours of normal recreational use, according to BRP.

Honda marketing manager Senger says 4-strokes can run tighter tolerances than 2-strokes, which expose pistons and rings to a lot of wear with so many ports in the cylinders.

Shields says over the long run, a 4-stroke requires more service than a 2-stroke. Some might require valve adjustments or replacement timing belts.

Capt. Joe Frohnhoefer — chairman and CEO of Sea Tow Services International, whose fleet is equipped with close to 2,000 engines — notes that a 4-stroke powerhead has more working parts than a clean 2-stroke’s, which increases the chances of encountering problems.

Mostly people are reluctant to talk about engine life, due in part to the relatively young age of both engine types.

While there is some debate over actual service and maintenance costs between the two engine types, the initial cost of a 2-stroke normally is lower than that of a 4-stroke.

“Four-strokes are more expensive to build — there are more parts to them — so if you have a customer who is very concerned about the total engine price, [2-strokes] might be the right route,” says Clay Gaillard, communications manager for Mercury.

A 225-hp Mercury OptiMax retails for $15,639, a 225-hp Mercury Verado 4-stroke retails for $17,335 (less rigging accessories), and a 225-hp Honda 4-stroke retails for $19,570. A 90-hp Mercury OptiMax retails for $7,972 whereas a 90-hp Mercury 4-stroke retails for $8,474. A 250-hp Yamaha HPDI 2-stroke retails for $18,150, a 250-hp Yamaha 4-stroke retails for $19,310, and a 250-hp Suzuki 4-stroke retails for $20,182. However, Yamaha’s F150 4-stroke at $13,200 costs $440 less than its Z150 HPDI 2-stroke.

Four-strokes have begun to dominate the market below about 40 hp because of the complexity and expense involved in trying to make a light, small engine operate with the electronic controls necessary to run a direct injection system. Mercury sells 4-strokes from 4 hp to 275 hp (including its Verado line) and OptiMax direct injection 2-strokes from 75 hp to 225 hp. It is discontinuing its old electronic fuel injection line of 2-strokes this year as part of a commitment the company made to the Environmental Protection Agency, Gaillard says.

A few years down the road, environmental regulations could take the decision between a clean 2-stroke and a 4-stroke out of the hands of boaters. While many direct injection 2-strokes meet California Air Resources Board 2008 three-star emissions ratings, some in the industry hold a view that any further restrictions would stretch 2-stroke technology too far. (The EPA is in the process of writing possible new rules.)

Yamaha still sells many of its popular, powerful and lightweight carbureted 2-strokes in addition to 4-strokes and HPDI 2-strokes. Yamaha’s Grigsby says the company’s HPDI lineup “is what it is right now” — 150 hp to 300 hp — and the company will be prepared if the 2-stroke market goes away in the next couple years.

At this point, 60 percent of the outboard market prefers 4-strokes, according to Suzuki district sales manager Jonathan French.

Zodiac’s Marie says BRP faces historical problems marketing its Evinrude E-TEC technology. Under Outboard Marine Corp., Evinrude’s FICHT technology, the company’s problem-plagued first attempt at direct injection, left a bad taste in dealers’ and consumers’ mouths, says Marie. Because of this E-TEC outboards might be difficult to sell, he says.

“In my mind, if they can overcome that, they’ll have a very serious and viable alternative to 4-strokes,” says Marie. “Clearly today the 4-stroke is an easier sale. Everybody has been 4-stroke conditioned.”

In the end, the choice might simply come down to personal preference.

“Some people have gas in their truck; some people have diesel,” says Kevin Skiba, national sales manager for Mercury Racing. “We’re going along with a dual strategy because we think there’s room for both.”