Boatbuilding Blog

January 7, 2007

2-stroke vs. 4-stroke engines

Filed under: Building - Considerations — tomlarkin @ 8:14 am

I’d always heard that 4-stroke engines were always more environmentally friendly, quieter, and more robust than 2-stroke engines, but I was just reading a thread on the WoodenBoat Forum and they mentioned a new 2-stroke called ‘E-tec’ by Evenrude.  It turns out that the new generation of 2-strokes can compete with 4-strokes and surpass them in many ways.

Here’s a Yachting Magazine article comparing them:,24579,1169547,00.html

All things being equal, a DI motor costs less and accelerates noticeably quicker than a comparable four-stroke. As for sound quality, and contrary to perception, DI motors register a few decibels quieter.

Here’s Evenrude’s E-tec home page:

E-tec won an environmental award from the EPA:

2004 Clean Air Excellence Awards Recipients

Evinrude® E-TEC™ Clean Air Technology
Bombardier Recreational Products Inc.

In 2003, Bombardier Recreational Products Inc. (BRP) introduced Evinrude E-TEC, an outboard engine for marine recreational products, which is based on a two-stroke engine technology. Compared to a similar 2004 four-stroke engine, carbon monoxide emissions with Evinrude E-TEC are typically 30 to 50 percent lower; and at idle are lower by a factor of 50 to 100 times. In addition, Evinrude E-TEC emits 30 to 40 percent less total particulate matter on a weight basis than a similar “ultra-low emissions” four-stroke outboard. Furthermore, oxides of nitrogen and hydrocarbon emissions for Evinrude E-TEC are similar, if not lower, than a four-stroke outboard. There are no oil changes with this engine, as well as no belts, and no valve or throttle linkage adjustments. This makes Evinrude E-TEC engines easier to own than comparable four-stroke engines. In addition, numerous advancements combine to create the Evinrude E-TEC quiet signature sound including an exclusive idle air bypass circuit.


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