Secrets Behind Evinrude’s E-TEC 250 H.O. Performance - 05/12/2010
For the last couple of years our reader mail has been growing with praise for the Evinrude 250 H.O. 2-stroke engine. Last year we did a survey of all marine outboard brands and the result was surprising: Evinrude had a greater percent of positive comments than any other brand. Say what? Yup, and this wasn’t advertising hype or a bunch of ditto heads yammering in an on-line chat room; rather, this was unsolicited reader mail, and most was quite positive.
At first we were surprised at the results. Weren’t the terms “high-tech” and “two-stroke” in the same sentence supposed to be an oxymoron? Evidently our readers – people who actually owned and used these things week after week -- didn’t think so. It was then that we realized that for years we – like everyone else in the marine business -- had been drinking the 4-stroke Kool-Aide. Thanks to our readers we decided to start drilling down into what made the Evinrude 250 H.O. 2-stroke engine tick.
The Back Story
Evinrude is part of BRP which makes Sea-Doo PWCs and boats, Ski-Doo snowmobiles and Can-Am ATVs and Spyder roadsters. BRP is a stand-alone company that is partially owned by the Bombardier family, founders of Bombardier, Inc. a multi-billion dollar Canadian conglomerate that makes commercial jetliners and high-speed trains. In other words, this is not a rinky-dink machine shop hiding behind the razzmatazz of high-priced promotion.
In 2000 Outboard Marine Corp (OMC) reportedly sold 175,000 outboard motors world-wide (about 1/3rd of the market that year) and on December 22nd filed for Chapter 11 protection during one of the biggest economic booms America had ever seen. Two months later BRP bought the company, getting some old plants and machine tools and some controversial 2-stroke technology that had been beaten up badly by the onslaught of 4-stroke engines from Japan in the 1990s.
The EPA was tightening outboard emissions standards, and California had announced very tough carbon emission standard that were going to take effect in 2008. The Federal government was going to follow a year later – making the future of 2-stroke engines problematical. The first thing BRP did was to clean house, and bring in its own management and engineering teams.
Job One is Square One
Next, BRP’s Evinrude engineers were tasked with totally revamping the brand’s product line along and with meeting the coming state and federal emission standards. BRP could have killed two birds with one obvious stone – a 4-stroke engine. Instead, George Broughton, Director of Engineering for BRP in Sturtevant, Wisconsin, and his team decided not to create yet another line of 4-stroke outboard products, but rather take 2-stroke technology to a whole new level.
At the time, some of Detroit’s engine designers were flirting with the notion of making 2-stroke motors for automobiles because of their many inherent advantages, but they were stymied by emissions problems. Broughton and his team thought those obstacles could be overcome for marine engines.
By the middle of the decade the BRP engineers had created the Evinrude E-TEC family of 2-strokes engines. Not only did they meet CARB standards, but they were also very low maintenance. The first tranche of engines were two cylinder motors ranging from 40 to 60 hp, and three cylinder engines ranging from 75 to 90 hp. Everyone knew that Evinrude needed a 250-hp engine, but that one was longer in coming.
Development of the Mighty Evinrude E-TEC 250
"The trick was to make an engine that would idle at 500 rpm and make 1 hp, and run 6,000 rpm and make 250 hp, while meeting the emission standards," says Broughton.
"The strength and duration of the injection pulse determine fuel droplet size," says Broughton, "which varies to meet the unique needs of the engine at any particular RPM." At low engine speeds, small droplets offer the greatest atomization. This is sprayed over the spark plug, and ignited as a stratified charge. At high speed, larger droplets are used to cool the top of the piston and provide more power.
E-TEC's method of direct injection is particularly uncomplicated and has fewer and smaller components than other systems. The fuel injectors are founded upon the concept of the common “Lorentz coil,” the permanent magnet and coil winding that is the heart and soul of a hi-fi loudspeaker.
A Lorentz coil is renowned for the way it can push and pull very quickly and for the way its strength and the direction of its pulse can be widely varied. That makes it ideal for spraying fuel into the combustion chamber at up to 600 psi. This precise control over the plume of fuel means engineers can make the engine do just about anything they demand of it, from one hp at idle all the way to maximum output at wide open throttle.
At low rpm, small droplets are sprayed directly over the spark plug and are ignited as a stratified charge. That lends the engine a smooth, clean idle, an essential operating characteristic when trolling. At higher rpm and horsepower, larger droplets cool the top of the piston. That builds maximum horsepower without wasting fuel.
Durability of the new Evinrude 250 was enhanced by use of a NASA-developed alloy two times stronger than conventional alloys at temperature. A swirl-nozzle fuel injector with 0.046-in. tangential slots is another key to clean combustion. "It's made through metal injection molding," says Broughton, "and starts as a piece about three or four times bigger than the final product. Then it's shrunk to size in an oven like a new pair of blue jeans in the dryer." The fuel rail is pressurized to 30 psi, and the Lorentz coil amplifies this to 600 psi (1,000 psi is possible, but as yet unnecessary) under wide-open throttle conditions.
A Magneto Makes Plenty of Spark
The E-TEC's electrical system is based around a magneto. Magneto ignition systems have been around since the late 1800s and are more reliable than battery coil systems. That is why they are used on most piston-powered aircraft. "The magneto produces from 150 to 300 volts," says Broughton, "but that is reduced to 55 volts to drive the oil and fuel pumps and the fuel injectors. It's further reduced to 14.7 volts to charge the battery.”
Evinrude E-TEC engines are designed to start within one revolution. The key to that kind of reliability is the sealed fuel injection system. Though the fuel in the gas tank may oxidize over time, no air can enter the engine's fuel system itself. The gas stays fresh. As the flywheel starts to turn, the magneto sends current to the engine controller, which determines where the piston is, when to inject the fuel and when to fire the spark plug -- all inside of one revolution!
"The Evinrude E-TEC is designed to go three years or 300 hours without any dealer scheduled maintenance," Broughton says. At the end of three years, only a few simple things are addressed such as spark plugs and gear lube. At that point, the engine is ready to go another three years or 300 hours without dealer scheduled maintenance.
All E-TEC engines have cylinder blocks manufactured using the “Lost-Foam” casting process that allows very complex shaped aluminum castings, with a minimum of joint lines and gasket surfaces. This process is extremely advanced and superior to more traditional casting techniques, such as sand casting.
For example, with the “Lost-Foam” casting method, complex internal passageways are in the mold itself, not formed by milling and grinding, they are therefore smoother and less likely to pit and corrode. The thickness of the block’s walls in delicate areas are more rigid with a reduced chance of failure. Overall, blocks cast with this method are less likely to corrode prematurely which prolongs life, particularly in a saltwater environment.
Closed Desk Design
The Evinrude 250 H.O. is a V-6, loop-charged engine with all cylinders and the exhaust manifold in a mono-block casting, including a closed-deck design for better cylinder bore support. This design helps keep the cylinder bore round during over-heat conditions, significantly extending the life of the engine.
Special Alloys and Coatings
The pistons are also made with the new alloy developed from the NASA Space Program that is twice as strong as conventional pistons alloys, at normal operating temperatures. The new pistons also have a longer, fuller skirt design, without ports, for a closer fit in the cylinder, less vibration, and much lower noise in operation.
CNC machined ports and Boron-Nitride honed cylinder walls mean extremely accurate bores that do not require the operator to follow any break-in procedure. Unlike competitive engines, an Evinrude E-TEC can be run at wide open throttle, right out of the box. So consumers never have to compromise how they use their boat.
The boron-nitrite hone amplifies surface porosity. Porosity retains oil like a sponge. The slick surface, the precision, the computer-aided machining and the special piston alloy all contribute to decrease initial wear to the point where break-in is unnecessary. For this reason Evinrude eliminated the de rigueur 20-hour scheduled check-up. In fact, dealers don't need to see E-TEC motors until 300 engine hours, which for most boaters is about three boating seasons, and then the next scheduled maintenance is another 300 hours away.
Summary of the Evinrude E-TEC 250 H.O.
The 250-hp Evinrude E-TEC engine is a 3441cc V6 that comes in 20” and 25” shaft lengths that weigh either 507 lbs or 515 lbs, respectively. Both versions come with the FasTrak™ Power Trim and Tilt, featuring a unique trailer support system that reduces wear and tear on boat transoms during transit.
The points touched on above only scratch the surface of the engine architecture, engineering, capital investment, and just plain expense that goes into to building each and every Evinrude 250 outboard motor. But by drilling down we have gotten an idea of some of the reasons why the 250 is getting such rave reviews from people who own them. Let’s face it. With an MSRP of about $22,000 no 250-hp outboard motor is cheap. And for that kind of money you deserve to get a reliable, high-performing, low-maintenance, fuel-efficient piece of machinery that should last decades.