The Last Triple-Cylinder Two-Stroke from Polaris: Polaris XCR 800 The Last Triple-Cylinder Two-Stroke from Polaris: Polaris XCR 800
(Originally published in the December 2018 issue of SnowTech) Today if you’re a Polaris diehard, the motor everyone is talking about is the new... The Last Triple-Cylinder Two-Stroke from Polaris: Polaris XCR 800

(Originally published in the December 2018 issue of SnowTech)

Today if you’re a Polaris diehard, the motor everyone is talking about is the new 850 Patriot. This engine is today offered in the 2019 XCR, but back in 2003 the XCR was built around a 794cc three cylinder Fuji engine. The XCR 800 of 2003 was built for the rider that wanted to be first across the lake and loved the triple pipe exhaust note that only a triple piped triple can produce. The only thing in common today with the XCR 800 sold 16 years ago is the XCR name and the P85 drive clutch, and the fact they both still have a track and two skis.

The demise of the three cylinder two stroke is still a sore spot with many sledders today. How could an engine that put Polaris at the top of the sales charts for two decades in the 80’s and 90’s suddenly become yesterday’s news and disappear after the 2003 model year? The answer at the end of the day comes down to you, the consumer. What you buy is what you get.

History Lesson

Polaris was synonymous with three cylinder engines starting in 1970 powering the TX race sleds. There first production triple was offered for sale in 1972 with the 502cc triple free air in the TX 500 LTD. The first liquid triple was offered in the 1979 Centurion 500 which would morph into the Indy 600 and Indy 650 of the 80’s and 90’s.

Surprisingly, Arctic Cat, Ski-Doo and Yamaha all continued to build twin cylinder engines with Arctic building a 650cc Wildcat in 1988. Ski-Doo would introduce the 521cc Rotax with RAVE in 1989 and followed that up in 1991 with a new 617cc Rave equipped Mach 1. The popularity of muscle sleds was born on the race track with the Formula III class featuring full mod 650cc motors of the day. The boys at Roseau soon started work on the next generation triple which would abandon piston port induction for case reed. The 1993 Storm featured a new Fuji 744cc that put 130 plus hp. Coincidentally Ski-Doo and Arctic Cat would also release their first consumer triples in 1993. The race for muscle sled supremacy was on!

1993-95 Storm – 1st and 2nd Gen Case reed triple

The first case reed Fuji/Polaris triple would turn out to be a very “peaky” motor. You could be cruising down the trail at 40 mph and then suddenly the engine would surge and the power would come on. The power would just start building as the RPM’s increased and the track would break loose. The motor really liked to run at WOT (wide open throttle) and man it would scream. Engineering redesigned the top end of the motor increasing the bore, redesigning the heads and pistons and bumped the displacement from 744cc to 794cc for the ’94 model year. The result was more predictable throttle response across the entire throttle range.

Polaris Storm

The 94/95 Storm motor however did reveal another durability issue when the throttle was held to the bar for long periods of time. A minority of owners reported a loss of engine rpm and power. Polaris engineering tore these motors apart and discovered that piston temperatures were reaching near the molten state of aluminum right on the edge of the exhaust port. Engineering realized that piston forces would cause the material to peen out and pinch the ring creating a “knife edge” above the dome of the piston. The owner would soon see a loss in power. Engineers believed the pipes were not tuned properly and were pushing too much heat back into the cylinder. The cast iron cylinder liners of the day would retain heat longer, compromising heat transfer to the water jacket in the cylinder. Add in the tight living space for the triple pipes and you can understand why under hood air temperatures could be an issue.

1996-98 Storm – 3rd Generation Case Reed. “Dealing with the heat of the motor and customer”

The ‘96 versions were the third iteration of the case reed triple, this time designed with Nicasil cylinder liners to improve heat transfer while still allowing tighter cylinder tolerances. The early Storm engines did not have a pressurized coolant system which was dealt with in ‘96 with a thermostatically controlled system using a surge tank and overflow bottle. The new “Aggressive” body work introduced for 1996 increased the under hood room for the triple pipes to improve performance and heat dissipation. An additional heat exchanger mounted at the rear of the tunnel added weight but was extra insurance to keep the engine cool in low snow conditions. The result was an engine that would run cooler and on the dyno put out 144 hp @ 8000 rpm.

Polaris Storm

While this was an improvement in performance and engine reliability, the Storm had developed a bad reputation based on the ‘93-‘95 model years when engine durability and performance was down compared to the competition. The last year (1998) of the Storm with the Aggressive body work and 3rd generation case reed triple was not a big seller as the Storm was now competing against the likes of the just released 1000cc triple Thunder Cat and 700 triple Yamaha SRX with electronic power valves (an industry first). If the brand new big iron from the competition was not enough, Polaris itself was moving away from Fuji built engines to their own domestic engine program.

This was an interesting time in the industry with Yamaha’s late entry into the triple-piped triple market in ‘98 just as triple sales were peaking. The rest of the industry knew Polaris had struck a home run with the mono block XLT triple, selling as many as they could. There still seemed to be enough demand for triples in the market, but by 1998 sales were starting to taper off. The new twin cylinder 600/700 engines were starting to gain momentum in mid-level performance models but there still was demand in the “hyper sled” market. Polaris engineering in Roseau meanwhile were putting on the last dyno hours on the 4th generation case reed triple that would be revealed for the 1999 model year. In the words of Greg Hedlund, “We saved the best for last.”

1999-2003 XCR 800 – The final years of the Fuji Triple

The 4th generation XCR 800 motor is today remembered as the best three-cylinder engine Polaris built. There have been iconic three cylinder Fuji/ Star/Polaris triples over the years. The 650 free air triples that powered Bob Eastman and Jim Bernat to World Championships in 1973 and 1975 were impressive looking motors. The 440 liquid triples that the Midnight Blue Express drove in 1977/78 in the RX-L racers were unbeatable. The iconic Indy 600/650 and Indy XLT triples were the market leaders in the 80’s and 90’s.

Polaris XCR 800 - Fuji Triple

The last Polaris triple introduced for the 1999 model year was the first Polaris motor to be equipped with Mikuni TM flat slide carbs. The Mikuni TM application would expand to all the Polaris domestic motors right up until the advent of the first Cleanfire injection in 2005 on the Fusion 900. Polaris would equip the TM carbs with a throttle positon sensor and a coolant temperature sensor. This first digital ignition would retard ignition timing as coolant temp increased to prevent engine burndown. Those early Storms with the “knife edging” of the pistons sure would have benefited from this ignition and made a lot of riders less upset with the ignition timing retarding instead of melting pistons!

Polaris XCR 800

The big feature on this motor was the Polaris Variable Exhaust System (VES) which from the outside looked identical to the domestic motor VES of the day. The secret was a resonance chamber machined into the casting of the exhaust port that allowed this short stroke triple to produce low end torque values comparable to the 800 VES domestic motor of the day. When the exhaust valve was fully open the stock 800 was capable of 150 plus hp @ 8100 rpm which allowed you to wave bye-bye to your buddies on their new 800 domestic twins (see charts below compiled from data taken from Dec.1998 SnowTech and Winter 2002 SnowTech).

Polaris triple XCR 800, Storm
Polaris triple XCR 800, Storm

The resonance chamber VES was stumbled upon initially by engineering working on a decompression method to reduce compression for easy starting. This evolved into a resonance chamber which acts as a two-stage variable exhaust. Today the opening is controlled with a servo motor based on programmed mapping. Triples with their shorter strokes do not generate the bottom end torque of a big bore twin. Polaris with the resonance chamber and VES could actually increase bottom end torque comparable to their 800 twin (see torque chart below).

This crude but effective “resonance chamber” was exposed (open) to exhaust gasses at low engine rpm. The resonance chamber would assist the reflected exhaust wave in the expansion chamber to arrive at the exhaust port with positive pressure when the exhaust port was not fully open. This “ram charging effect” would return unburnt fuel back into the engine, the same way the expansion chambers are designed when the exhaust ports are fully open. It was a brilliant idea and it made this new motor come alive on the bottom end. On top end the big triple pulled on the dyno 152hp @ 8200 rpm. This is what puts a big smile on your face!

The new triple was installed into the Gen 2 body work in 2000 where it would remain there until the last year of production in 2003. The new body work and ergos combined with a full CRC (controlled roll center) trailing arm IFS up front with and XTRA-10 coupled rear skid frame was state of the art for a Polaris production sled. Essentially you had the XCR 440 chassis with an 800 triple. What was not to like! This chassis was great in the bumps and reduced bump steer significantly. The big negative (even with a kick butt triple) is the extra weight. The XCR 800 added an additional 57 pounds over the Liberty 800 twin. All of that extra mass located up front over the skis made these sleds tougher to go through bumps as quickly and were a handful to wrestle around a corner if you entered just a little too fast. Essentially you had the same problem that riders of 4-stroke sleds have today.

What happened to the EDGE Chassis 800 Triple?

A question that always remained is did Polaris consider putting the 800 triple into the EDGE chassis? The answer is yes and prototypes were built. Just check some of the XCR 800 owners group pages on social media and you will see some examples of home built EDGE 800 triples. Polaris marketing knew they had the triple that was reliable and quick but was the cost to gear up for tooling to build an EDGE 800 triple going to give the return on investment needed for the bean counters? Sales in 2003 had dwindled to just 500 sleds sold. The triple pipe music died in 2003 at Polaris in favor of the new domestic twins that Polaris was banking its future on.

What’s Past is Prologue

As we enter the 2019 model year we once again see history repeating itself with displacement escalating to 850cc in the big bore twins. Performance is king and snowmobilers love to know they have more power under their thumb than they need. What next? A 900 twin? It’s been done before and history seems to repeat itself. At the end of the day the consumer (you) decides what the manufactures build. Spending your dollars makes their decision for them.

By Hal Armstrong – SnowTech Canada

Follow Hal Armstrong and the Vintage Rider section in SnowTech Magazine, and follow Hal on Facebook @sledtimemachines.

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