All signs of life have faded…the two-stroke is dead.
Long live the two-stroke!
If you’re a powersports enthusiast over the age of 30 then you’ll remember when the two-stroke ruled the roost…and you’ll also remember when it all came crashing down. No matter what you rode on or in, someone stuck a new four-stroke engine in it.
Snowmobiles, boats, personal watercraft, off road motorcycles…you name it, the brap was going away.
But now in some areas of powersports the brap is trying to make a comeback. Cleaner, meaner types of two-stroke engine technologies are trying to claw their way into the showroom.
Two standalone research projects that caught our attention early on were the Omnivore and Grail two-stroke engines, and both helped keep the dream alive in some way, if even just to show that someone was trying to make two-strokes work.
In 2008, Queen’s University Belfast, Lotus and Jaguar developed the Omnivore, a two-stroke engine that featured variable compression ratios, which resulted in much lower “dirty” HC emissions and better fuel savings as a bonus. The engine was also said to use a monoblock design joining the cylinder head and block together, reducing weight and featured the Orbital FlexDI fuel injection system, reducing emissions and improving scavenging characteristics.
Around the same time we heard about the Grail, as both engines were referred to in the New York Times. The Grail apparently had some lofty goals (100MPG and a 1 liter design) but has so far failed to deliver a production version since they began.
Grail describes the engine’s operation in detail:
“Compression takes place within the reed valve air box, pre-compression chamber, vent-to-piston ports, piston-intake-ports & crankcase. As the piston travels upward creating a vacuum beneath the piston, fresh air enters via the intake air box through the one-way reed valve, and fills the external pre-compression chamber, vent-to-piston ports and piston-intake-ports with fresh air.”
“Compression occurs within the cylinder as the piston travels upward. At Top Dead Center (TDC), direct ignition then single or multiple ignitions occur. This forces the piston down into the cylinder compressing air in the engine crankcase, external pre-compression chamber, vent-to-piston ports and piston intake-ports. “
“Just prior to Bottom Dead Center (BDC), the exhaust valve opens via a standard cam/push rod mechanism or electro-mechanical valve control. Exhaust gases exit via the exhaust valve opening at the top of the cylinder. Compressed fresh air enters the cylinder via piston valve, which forces out the final exhaust. As the piston travels past BDC the exhaust valve and piston valve close and cycle repeats.”
More encouraging is the ongoing use of two-strokes in both snowmobiles and marine outboard engines. Even though most manufactures slated the two-stroke for failure and elimination from their lineups, a few hunkered down, listening to their huge client base and made the two-stroke more efficient and cleaner in the process.
Let’s look at some snowmobile technologies:
Ski-Doo claims that their Rotax E-TEC Direct Injection (DI) 800cc sled with both DI and precision oil-injection/metering technologies results in the highest HP/weight ratio as well as the lowest emissions in the 800cc class. This is a serious enthusiast engine with a strong following in this segment. See a video of the E-Tec in action HERE.
Polaris says their CleanFire2 Injection is the way forward. In this configuration, low emissions and high performance are the goals and Polaris uses a combination of DI technology but this time feeding the transfer ports, coupled with a precision Throttle Position Sensor (TPS) and proprietary Detonation Engine Technology (DET) to produce a fast revving sled that’s light with low emissions, but keeps a high HP/weight ratio.
And in the boating market:
You still find two-strokes still in the outboard engine segment, with Evinrude taking advantage of the E-TEC direct injection technology by its parent company Bombardier and successfully proving again that the DI/oil injection setup is perfect for lightweight power to weight ratio applications.
Mercury Marine has a strong lineup of what they call “two-stage DFI” engines that feature direct injection and also offer some measure of performance upgrades like carbon-fiber reeds and expansion chambers, while still burning cleaner than some opposition cc per cc in their class. Mercury claims the OptiMax 250 Pro XS burns 14% cleaner than some other 250HP four-strokes offered.
And then you have personal watercraft:
According to the PWIA, “Personal watercraft today are 75 percent quieter and up to 90 percent cleaner than pre-1998 models.” Now that’s an incredible statistic and shows that the PWC industry saw the end in sight and stepped up to the plate, the problem for two-stroke fans is that they pretty much dropped all support for the two-stroke and put their development efforts behind the four-strokes with great success.
But will these successful types of powersports two-stroke technologies make their way into off road motorcycles? Well a few manufacturers might think so as evidenced by these rumblings:
KTM - Highly efficient with a tremendous weight to HP ratio, KTM two-strokes don’t feature any type of space age engine technologies today, but you can be sure that KTM has been working on a DI based engine for the two-stroke range. These rumors have been bandied around in the off road press for well over a year now, although rumors that the engine is overly complex and may be almost the same weight as a four stroke powerplant are also rife, which may explain KTM’s reluctance to bring these variants to market.
KTM Product Manager Joachim Sauer recently stated in AustralasianDirtBike:
"We have been working a lot in recent years in order to get the injection system ready for our two-strokes. I went out into the market last year and visited lots of dealers and spoke to hundreds of riders and I asked them if they would like a two-stroke injected bike. Everyone said, 'Great! When will it be ready?'
"I then said, 'Would you still love it if the price was close to the 450/500 EXC?' Also, instead of just a carburetor and ignition, you would have to deal with pumps and all the complexities of such a system, which also adds 2kg of weight. It would make the whole thing so difficult to deal with you would not be able to change the piston at home anymore.
"From the beginning, I could see their enthusiasm get less and less, and at the end, out of 100 people I asked, there was not even five people who would like such a system. So we decided we won't introduce it until the rules (homologation) force us to introduce it. This will probably happen with model year 2017. But if we had to do it next year, we would be ready. But we want to keep it back and do some more testing. "
OSSA - Historic brand OSSA introduced the prototype Enduro 250i and 300i models in 2012 which featured a two stroke powerplant with a semi-reversed cylinder head and a dual fuel injector setup, with one on the crankcase and one in the head and some of these items are found on the models you can buy today. No production of the Enduro models been announced as of the time of the writing of this article.
But that’s not a lot.
Newer two-stroke technology is still out there on the showroom floor in the applications that can support it like boats and sleds, as PWC’s have effectively made the switch.
Prototype technology in off-road models from manufacturers like KTM/Husqvarna and niche brands like OSSA may keep the hope alive for a while longer, but two-strokes have a lot of catching up to do in the off-road arena.
To be viable alternatives to cleaner burning four-strokes, not to mention the coming wave of high performance electric bikes, two-strokes off road bikes will have to radically change their game in order to survive at all. In terms of applications on our off road motorcycles, it appears that the weight and complexity of these systems, coupled with higher weights and costs, outweigh the benefits to the average consumer.
It was the EPA. Then they got rid of the open class. As 4 strokes could not compete at the 500cc level.
And 250cc 2 strokes had to compete with 450 4 strokes. 250 4 strokes with 125 2 strokes etc.
At least get the history right if your going to talk about it. Rather than making crap up. Thanks.