For many kinds of boating, the outboard motor is the answer. But it comes with questions, too — which is better, two strokes or four? What's the right prop? Is the bigger motor the better motor? We've presented a few of the most debated questions to the experts, and here's how they answer them.
Question: Are four-strokes always better than two-strokes?
Answer: Are Fords better than Chevrolets? Paper better than plastic? When it comes to outboard power, the question is four-stroke vs. two-stroke. If you believe what you hear, the answer is etched across the stone board — four-strokes rule. But dig deeper and you find the answer isn't so clear.
First, the technical distinction. Four-stroke outboards, like the engine in the car in your driveway, burn straight gasoline within cylinders, circulating lubricating oil through a separate system. Oil and gas don't mix, unless there's a breakdown. Two-stroke engines, in contrast, burn a blend of gas and oil.
Traditional two-strokes were fed their oil-gas mix fuel by carburetor or injector into the cylinder through an intake valve. During part of this feeding, the exhaust valve was also open, and up to 30 percent of the fuel escaped unburned.
Jump ahead to two-stroke direct-fuel-injection (DFI) engines. The fuel is sprayed into the cylinder with precision timing while the piston covers the exhaust valve. There's no loss of fuel. (In four-stroke engines, thanks to their four piston strokes per cycle, intake and exhaust take place at separate times.) DFI two-strokes and four-strokes both deliver much better fuel economy than traditional two-strokes, since they're directed by computer and burn virtually all of the fuel.
Evinrude's E-TEC two-stroke DFI engines inject fuel twice as fast as standard direct injection, even adjusting the fuel delivery and oil-gas mix as needed. We've tested the E-TEC engines, and they're just as smooth and almost as quiet as four-strokes while maintaining more traditional two-stroke power.
On the other side, four-stroke motors are also erasing what was a clear division just two years ago, the one that said two-strokes are inherently more powerful. The industry once envisioned a 100 hp limit for four-strokes because of their extra weight. But the limit has vanished. Witness Suzuki's new 300 hp, at just 604 pounds.
"It's a closer call than ever before," says Mercury spokesperson Eric Pope. "The biggest myth is the idea that two-strokes are noisy, smelly and not very fuel efficient. It isn't true today."
Two versus four is now more a matter of boater preferences than ground-shaking practical distinctions. Through it all, both modern four-strokes and DFI two-strokes are mechanical marvels.
Difference, What Difference?
• Two-stroke DFIs are lighter than four-strokes with the same power, but the difference is shrinking.
• Four-strokes are quieter than two-strokes, but the difference is shrinking.
• Two-strokes generally provide a stronger hole shot, but the difference is shrinking.