The Life and Times of the Two-Stroke Triple The Life and Times of the Two-Stroke Triple
For several decades the ultimate high performance snowmobile was powered by a three-cylinder two-stroke engine. The 120-degree firing sequence of a triple is sexy... The Life and Times of the Two-Stroke Triple

For several decades the ultimate high performance snowmobile was powered by a three-cylinder two-stroke engine. The 120-degree firing sequence of a triple is sexy and very addictive. For many snowmobilers there is no better sound on the planet than that of a triple-piped three-cylinder two-stroke engine singing at high rpm levels. Memories of sleds like the SRX, Mach Z, XCR 800 and ZRT should make us all smile.

Yamaha Triple Triple

By the late 90s, big-bore twin engines like the Rotax 670 and Polaris 700 were rising in popularity and by 2006 the triple party had ended, seemingly rather suddenly, much to the dismay of many.

It has now been more than 10 years since a two-stroke triple has been crated at the end of an assembly line. The advantages of a three-cylinder engine are still utilized in many of today’s four stroke engines, including the most powerful production sleds ever produced in the Yamaha Sidewidner and Arctic Cat’s latest 9000- Series models, including the all-new Thundercat. The demise of the triple-cylinder two-stroke continues to puzzle for many of us and this story will look at the origins right through to the end when a host of changes in the snowmobile business silenced what many call “The National Anthem of Snowmobiling”.

The Hirth Honker

The popularity and growth of snowmobiling in the late 60’s was akin to the smart phone of today. Everyone in the snow belt was buying one or seriously thinking about it. People bought a single-cylinder 12hp sled and once they became more comfortable with riding a machine in the snow they typically opted for a sled with more power. More power meant more cylinders and larger displacement. The birth of the twin cylinder 340,400 and 440cc engines soon followed for production snowmobiles.

Hirth Honker Triple cylinder

On the race track the hp race was escalating when the 634cc and 744cc twin-cylinder race sleds emerged. The summer of 1968 at the annual USSA (United States Snowmobile Association) rules meetings had on the top of the agenda a call to put a limit on engine size. The horsepower race was getting out of hand, it was concluded (sound familiar?). The limit was set at 800cc entering the 1969 race season.

The majority of engine suppliers at the time were primarily European (Hirth, JLO, Sachs, Kohler and Rotax). That would change for the 1970 season when Polaris introduced their “Star” engine built exclusively for Polaris by Fuji Heavy Industries (Subaru). Polaris would race their new 649 and 795cc free air triples combined with their new aluminum flyweight clutch to many race victories. Arctic Cat was just beginning to develop an alliance with Kawasaki, which was chomping at the bit to enter the snowmobile market. Kawasaki had already released their three-cylinder free air street bikes which were real fast and Arctic Cat wanted that power in their race sleds. For 1970 Arctic Cat, among other manufactures, would use the new Hirth “ Honker” free air triples. The 647cc produced 65hp@7000 rpm and the 793cc was rated at 82 hp @6500 rpm. Ski-doo introduced their new Blizzard race sleds in 1970 with 636 and 776cc twins. Ski-doo had a successful season in 1970 but the writing was on the wall. The horsepower war was ramping up and to compete with the “Honker” motors Rotax would up the anti in 1971 with new free air 645 and 797cc triple/triples.

1971 Ski-Doo Blizzard 797cc Triple cylinder
1971 Ski-Doo Blizzard 797cc Triple cylinder
1971 Ski-Doo Blizzard 797cc Triple cylinder

The First Triple-Triple Wars

The 1971 season would see the manufactures expand their three-cylinder engine offerings. The new Ski-doo triple-cylinder Blizzards were built on a wider tunnel using a 16.5” wide track vs. the 15” track used on the twin-cylinder versions. The ‘71 Blizzard had these big triples sitting right there in your lap with the motor mounted on top of the tunnel. The Rotax triples used a short stroke 61mm crank. The 645 featured a 67mm bore putting out 71 hp and the big 797 was a punched out version with a 74.5mm bore putting out 88 hp. The over-square triples (bore diameter larger than stroke length) could now rev higher and that typically meant more peak HP. The tradeoff was less torque (bottom end) with the shorter stroke motor. The sound was incredible from the triple pipes!

In 1971 Polaris built a 439cc triple in addition to their 649cc and 795cc motors. These were 6-port motors and featured CDI ignition. Jerry Shank was the lead engine developer at the time and tells us the triples were supplied originally with Tillotson carbs until they were able to solve a fuel foaming problem with the Mikuni carbs. The solution? Rubber boots to isolate the carb from the engine cylinder vibration. The cranks also featured double row bearings on the PTO end to better support the new aluminum flyweight clutch.

1971 Polaris 649cc TX 2+1 triple cylinder 3 cylinder
1971 Polaris 649cc TX 2+1

Arctic Cat now had their Kawasaki motors but there was no triple ready for 1971. They did however have the big 800cc 4-cylinder free air – the King Kat. This package was rumored to put out close to 100hp and in a straight line they were the fastest sled on the snow. The problem was all that extra weight meant it did not want to turn. Overcoming all that inertia (tendency of an object to reduce change in velocity and direction) overshadowed all that power. Sound familiar with some of today’s sleds?

1972 would see the proliferation of triples continue. Arctic Cat would finally get their triples in 400, 440 and 650 cc. Arctic Cat would not build an 800cc triple until the ZRT 800 in the late 90’s. Ski-doo took the triple one step further with 293, 340, 645 and the 797cc engines, all triples. Ski-doo moved from single cylinder 291 and 336 cc free air singles to three cylinder 293 and 340 triples built around a 50mm stroke that put out 42 and 48hp respectfully. Again, small bore, high RPM engines with triple pipes provided increased volumetric efficiency (ability to fill the cylinders with the fuel-air mixture) and allowed these engines to be the HP kings in their class. Ski-doo also created their first forward-mounted engine chassis in 1972 for these new triples. The extra weight over the skis now improved the sleds handling in the corners and allowed a jackshaft mounted secondary and separate chaincase to lower the sleds’ center of gravity and better align the secondary and chaincase.

1972 Blizzard 293cc triple
1972 Blizzard 293cc triple

1972 was also a year for firsts in two other significant areas. The first production triple available to the general public was the 1972 TX 500 Limited from Polaris. The 502cc piston port free air triple was built with a three into one exhaust. Polaris would build the 500 free air triple until the 1975 model year.

1972 Polaris TX 500 Limited
1972 Polaris TX 500 Limited

The performance triples were all free air engines and as they continued to evolve and make more power, dissipating heat was becoming more of an issue. Mild temperatures reduced the cooling efficiency and that meant power dropped as the engine temperature increased. Cool engines make more power and resist detonation better. The immediate solution? Larger cooling fins on the heads and cylinders and even the crankcase. They looked awesome but engine mass continued to increase. Features like chrome cylinder bores which improved heat transfer to the cooling fins were an improvement but costly to repair. The OEM’s were in a dilemma. With sled sales plummeting the move to liquid cooling was looked at by the bean counters with raised eyebrows. Race sleds maybe, but production sleds? Not a chance. That is where a small start-up company run by a group of engineers had a better idea and were prepared to take the risk.

1972  Brutanza  Engineering  Brut 439cc triple
1972 Brutanza Engineering Brut 439cc triple

Brutanza Engineering was much like Tesla is today – taking state of the art engineering in non –mainstream engine technology. Developing a liquid-cooled two-stroke engine for a snowmobile application was much like electric motor technology today. Liquid cooled engines were all under development by the big four OEM’s when the visionary Brut was released in 1972. The Brut would be powered by a liquid cooled 439cc triple using a radiator for cooling. This was a specialty snowmobile akin to the Yamaha Sidewinder/ Arctic Thunder Cat of today. It was a sled for those who had deep pockets and wanted the latest in technology. The Brut did reveal both the advantages and the challenges to build a liquid cooled snowmobile.

The Birth of the Muscle Sleds

The last free air powered snowmobile to win the World Championship was the 1975 Polaris 650 triple. The race rules changed for 1976 with the top race class capped at 440cc. The world of snowmobiling was changing in the mid 70’s. Sound regulations had resulted in more restrictive exhaust and intake noise solutions. Increased under hood temperatures were a problem for the consumer and warranty claims were rising over heat related engine failures. The push to move to liquid cooling was job #1 for the engineering departments. 1976 would see liquid cooled motors dominate on the racetrack. All the OEMs raced their new liquid cooled engines that year, some with success and others not so much. Racing forces companies to react fast if they are on the losing end of the chequered flags and for Polaris that is exactly where they found themselves. Ski-doo was now racing rotary valve intake liquid-cooled engines, which were the horsepower kings when it came to twin cylinder engines. The 440 Rotax race engines were pushing close to 120 hp. The rotary valve allowed the intake timing to be designed so less fuel would short circuit out an open exhaust port. The alternative to the piston port engine was the reed valve intake (as used today), which had its own set of problems in keeping the reed petals from self-destructing. Polaris did all they could in ‘76 by increasing engine rpm’s to increase power but vibration issues became a problem.

Polaris returned to their three cylinder roots in ‘77. The triple 440 with the shorter stroke could be spun at the higher rpms and combined with liquid cooling would make them competitive again in terms of power. The Polaris engine template for the next 25 years was born that year. The 1977 RXL with IFS sparked the imagination of sledders of all brands. Imagine having an IFS trail sled with a triple?

That dream would become reality in 1981. Polaris however did bring to market the Centurion, a 500cc three-cylinder liquid-cooled model, to dealer showrooms for two years (1979/80) in a conventional leaf spring chassis which was based on their successful cross country TX-L model. In retrospect this was a teaser sled for everyone that wanted an IFS chassis with the 500 triple. The first modern muscle sled in an IFS chassis arrived in 1981 – the Indy 500 Centurion set the snowmobile world on fire!

1980’s Polaris Indy 500/600 triple
1980’s Polaris Indy 500/600 triple

The other manufacturers remained solidly behind their twin cylinder LQ performance sleds and in terms of straight-line speed were just as quick as the Polaris triple. Ski-doo continued to market their high performance rotary valve twins in a conventional leaf spring chassis until 1985. Arctic Cat missed three years of producing a high performance IFS chassis and introduced their 529cc El Tigre 6000 in 1985. Yamaha joined the muscle sled IFS wars in 1983 with the 535cc Vmax. It was during this period of IFS chassis development and the push for more powerful liquid cooled engines that the last shakeout in the snowmobile industry occurred leaving us with our four remaining brands.

The economy and good snow across the snow belt in the mid 80’s gave a much needed shot in the arm for the snowmobile industry. The triple wars had not started yet but Polaris kept upping the ante culminating with the Indy 650 in 1988. Arctic Cat introduced their Wildcat with a new 650cc Suzuki twin featuring case reed induction, liquid cooled crankcase and a gear driven water pump. Ski-doo introduced the Mach 1 performance sled in 1989 with there new Rotax 580 rotary valve twin with the first production variable exhaust system (RAVE) which is an industry standard today.

The 90’s – The decade of the Triple

The 1990’s go down as the decade of the triple two strokes. Snowmobile sales were increasing year over year and would continue to rise, peaking in 1997 at over 260,000 units.

It started with Polaris offering EFI on a limited build 1990, Indy 650 RXL. It was the first EFI triple with 46mm throttle bodies and a primitive CPU by today’s standard that monitored 5 inputs to control the fuel/air ratio from idle to Wide Open Throttle (WOT).

1990 Polaris 650 EFI
1990 Polaris 650 EFI

Yamaha pulled out all stops in 1992 with the Vmax-4. Who was to know that a 4 cylinder two-stroke would hit the snow once again? It had been 21 years since the King Kat had made noise on the racetrack. Trust Yamaha to strike out on its own path. Yamaha engineering believed the benchmark was the Fuji triple used by Polaris at that time. Inherent harmonic vibrations in a triple design led to Yamaha developing a costly 4-cylinder with conjoined dual cranks as a response to the need for a flag ship model. Yamaha engineering believed the twin cylinder motors that Arctic Cat and Ski-doo were still using was limited in displacement to 600cc due to detonation issues given the lack of engine monitoring electronics and fuel induction technology available at the time. The Vmax-4 engine was two twin cylinder engines connected together with a counter-rotating shaft driven off the center of the crankshaft. The original 743cc quad also brought some new engineering features to the sport -Mikuni TM flat slide carbs for improved throttle response and digital ignition. Yamaha bumped up the 4-cylinder displacement in 1995 to 791cc putting out close to 150 hp. The motor was retired from production after the 1997 season when sales did not live up to expectations in the V-max chassis with telescopic strut ski suspension.

I found it amazing when researching this story how Arctic Cat and Ski-doo would both enter the market with triples in 1993. Ski-doo entered the market with their 774cc Mach Z triple/triple with RAVE, reed valve induction and Mikuni TM flat slide carbs. The new triple was also introduced in a new chassis with trailing arm IFS. Arctic Cat one-upped everyone with their 900cc Thunder Cat triple. The reed valve induction engine used 38mm Mikuni carbs and came with triple pipes. The unique feature of the motor was a balance shaft used to cancel vibrations from the 76.5mm diameter pistons.

Thundercat 900 triple-triple
Thundercat 900 triple-triple

As the engines grew in displacement and horsepower in the 90’s, chassis and suspension systems also were evolving. Racing as always had a big influence on future production sleds. The (1993) rules for the premier Formula III oval class now restricted engine size to 600cc again to reduce speeds. This resulted in new 600 triples that were to have less power than the 800cc run in previous years. It wasn’t long till the 600cc sleds were running just as fast. What was once considered a “big “engine in the mid 80’s was now referred to as a “baby triple”.

Polaris made a fantastic run with their XLT sleds featuring a mono block triple. The XLT was introduced in 1993 but was overshadowed in the muscle category by the Mach Z and the T-Cat introduction. Polaris engineers were already on a mission to simplify the triple engine to reduce weight and manufacturing costs. Working with Fuji the new engine featured a one-piece cast engine block and head. A three-into-one exhaust was a throw back to the 80’s once again. The XLT snowmobile came in at a weight of 475 lbs compared to the 500 lb plus triples that were gaining weight as fast as the engine size was increasing. Arctic and Ski-doo followed with 600 triples of their own in 1996 – the ZRT 600 & Formula III 600.

It became very apparent to Yamaha Sales and Marketing that the market wanted 3-cylinder engines regardless of engineering concerns and the existence of the Vmax-4. Yamaha marketing convinced corporate to design a new 700 triple with a single pipe to gain market share by offering what they believed their customers wanted. The success of the Polaris XLT was a trailing arm IFS chassis with a lightweight triple making the right noise. The VMAX 700 SX entered production in 1997 with a triple that was claimed to be the lightest on the market. Already Yamaha was looking at a triple that would compete in weight with the 670 Rotax producing similar torque and horsepower without the vibration issues of a big bore twin. This engine was bristling with the latest two-stroke technology (digital ignition, triple exhaust ports, Nicasil cylinder liners, Mikuni flat slide carbs). Power was rated at 120 hp, but the sound was what hooked riders. This engine is regarded by some as the sweetest-sounding triple of all, especially when fitted with triple pipes. Sleds fitted with this engine are still, to this day, sought after by collectors and vintage riders alike.

CA Pro skis

How popular were three cylinder motors in 1997? Polaris had 16 models using 5 different three cylinder motors. The following year (1998) that number dropped to 9 models with the introduction of the new Polaris Liberty 600 and 700 twins. The reign of the triples was not over yet. 1998 would see Arctic Cat introduce the 999cc Thunder Cat putting out 172hp. Yamaha introduced their triple-triple SRX 700 to compete in the muscle sled wars. It was the first engine with electronically controlled variable exhaust system.

Triples were also made available in two up sleds for the first time from all four manufacturers signaling another “war”. The 800 triple Pantera and Grand Touring models were real sleepers! Nothing beats blowing the doors off your buddies sled with you and your wife screaming by them on your 800 triple two-up sled.

As the muscle sleds continued to grow, three forces were present that would usher in the demise of the triple. Snowcross racing had started to increase in popularity in the mid 90’s. Chassis and suspension innovations were now being driven from terrain racing instead of the oval track. The spin offs from Snocross would trickle down to the triples. Second was the increased popularity of mountain riding. Ski-doo had introduced a purpose built sled for the steep and deep with the Summit 670 back in 1995. Ski-doo chose a big bore twin for a reason. Reduced weight, better maneuverability and big torque down low. Polaris quickly followed suit with their 1997 RMK 700, aiming for the Rotax 670. The triple two strokes were clearly not going to be the engine of choice for future mountain sleds.

The third factor was the new EPA emission standards being established in November 2002. The new EPA standard for snowmobile emissions was to be implemented in three phases. Phase one came in effect in 2006 with 50% of engines produced having to be compliant (EPA standard is 100 g/kW-hr HC and 275 g/kW-hr CO.) The first phase required a decrease of 30 percent of these pollutants, in complying engines, over the previous industry baseline.

Ski-Doo MACH Z

The last Hurrah of the two-stroke triple

Arctic Cat wound up production of their last triple in 2002. Their new 800 big bore twin had now captured the imagination of the performance snowmobiler. The ZR 800 weighed 75 lbs less than the T-Cat with the 1000cc triple. Around the corner in 2003 would be the new 862cc twin putting out 150hp in the ZR chassis that had been developed on the Sno-X circuit. Arctic Cat, like the other OEM’s, were working on making their new big bore twins compliant to the upcoming EPA standards in 2006. Ski-doo abandoned the Mach Z in 2003. The new REV chassis had just been introduced, along with a new 800 SDI motor that was already compliant to the 2006 EPA requirements.

Polaris Ultra

The company that started the triple-triple class shut it down after 2003. The XCR 800 was housed in the “Evolved” Gen II chassis while the new Liberty twins were all running in the EDGE chassis. The last 794cc Fuji triple featured case reed induction, 38mm Flat slide Mikuni carbs, Variable Exhaust and Digital CDI with triple pipes. Many consider it the best triple Polaris built over the course of 25 years, finally overcoming most of the issues with the Storm and Ultra sleds.

Ironically it was Yamaha, the four-stroke snowmobile leader, who was the last to build three-cylinder two-stroke snowmobiles, the last one being in 2006. Their technology peaked with the 2002 SX Viper engine featured self cleaning electronically controlled variable exhaust valves, 3-D ignition and rack mounted flat slide carbs that were coolant-heated to prevent freezing. The motor featured a three-into-one exhaust and forced air induction. The 696cc triple was mounted in Yamaha’s latest trailing arm chassis with a die cast aluminum bulkhead to increase chassis rigidity. While it was more powerful than the single-piped 700 triple it replaced, it was also heavier – not a great match for a sled being positioned in the bump sled segment.

Arctic Cat ZRT

Will Triples Make a Comeback?

I spoke with Greg Spaulding, 2-Stroke Engine Design Group Leader at Arctic Cat to get his opinion on why triples fell out of favor. Here is his take on the reason; “Yes the triples were popular in the 90’s and early 2000’s and sales represented that interest. As styling designs evolved to narrower bodies and twin cylinder engines began to grow in displacement and torque/power, the market slowly gravitated to those traits in a trail snowmobile. With that transition, it became increasingly more difficult for designers to envision packaging a triple cylinder 3-pipe engine in the smaller & narrower snowmobile chassis designs that were becoming the desired future.”

“We (Arctic) had discussed a new larger displacement triple to be available in the early 2000’s but the idea was dropped for a few reasons. Our current triple engine sales had been in decline over the previous few years indicating that the market was moving away from them, the triple sales numbers we were seeing for the upcoming model year had again declined, the cost of designing, developing and producing an all new triple did not appear to warrant the investment in an all new triple engine. Also for us, EFI was the choice for fuel delivery on upcoming 2-stroke engines and the difficulty in developing and calibrating a 2-stroke multi pipe engine with EFI is much more difficult than a single pipe due to the variation in pipe volume in mass production. Pipe volume inconsistency from cylinder to cylinder creates fuel-mapping troubles that are very difficult to overcome in mass production. And of course the additional weight, cost and packaging of a triple cylinder triple pipe engine in narrow & compact snowmobile chassis can be a challenge.”

“So in a nutshell, development costs, lack of sales numbers, vehicle cost and weight were the drivers in our decision to no longer produce triple-cylinder 2-stroke snowmobiles.”

Greg’s opinions echo many others I spoke to in the industry. We can all speculate that with today’s sophisticated engine monitoring systems and SDI fuel injection that a triple could be made EPA compliant. Current four stroke motors are shoe horned into today’s chassis so it comes down to how much extra would you be willing to pay to hear “Snowmobiling’s National Anthem” once again?

I spoke with Greg Spaulding, 2-Stroke Engine Design Group Leader at Arctic Cat to get his opinion on why triples fell out of favor. Here is his take on the reason; “Yes the triples were popular in the 90’s and early 2000’s and sales represented that interest. As styling designs evolved to narrower bodies and twin cylinder engines began to grow in displacement and torque/power, the market slowly gravitated to those traits in a trail snowmobile. With that transition, it became increasingly more difficult for designers to envision packaging a triple cylinder 3-pipe engine in the smaller & narrower snowmobile chassis designs that were becoming the desired future.”

“We (Arctic) had discussed a new larger displacement triple to be available in the early 2000’s but the idea was dropped for a few reasons. Our current triple engine sales had been in decline over the previous few years indicating that the market was moving away from them, the triple sales numbers we were seeing for the upcoming model year had again declined, the cost of designing, developing and producing an all new triple did not appear to warrant the investment in an all new triple engine. Also for us, EFI was the choice for fuel delivery on upcoming 2-stroke engines and the difficulty in developing and calibrating a 2-stroke multi pipe engine with EFI is much more difficult than a single pipe due to the variation in pipe volume in mass production. Pipe volume inconsistency from cylinder to cylinder creates fuel-mapping troubles that are very difficult to overcome in mass production. And of course the additional weight, cost and packaging of a triple cylinder triple pipe engine in narrow & compact snowmobile chassis can be a challenge.”

“So in a nutshell, development costs, lack of sales numbers, vehicle cost and weight were the drivers in our decision to no longer produce triple-cylinder 2-stroke snowmobiles.”

Greg’s opinions echo many others I spoke to in the industry. We can all speculate that with today’s sophisticated engine monitoring systems and SDI fuel injection that a triple could be made EPA compliant. Current four stroke motors are shoe horned into today’s chassis so it comes down to how much extra would you be willing to pay to hear “Snowmobiling’s National Anthem” once again?

Story by Hal Armstrong – SnowTech Canada

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