Fifty years ago the sport of snowmobiling (and the world we live in) was in a much different place than today. Snowmobiling was the fastest growing winter sport with annual sales peaking at just under 500,000 units. The economy was doing fine and all the distractions we have today (social media, Netflix & X-Box) did not exist. People were looking for an activity in the winter that they could do right from their front door with friends and family. The snowmobile was just the ticket.
Story by Hal Armstrong
Polaris Legend Dorothy Mercer racing the Polaris ATX
In the early 70’s organized trails were still in their infancy. A big ride was to travel 20-30 miles to the next town, have lunch and then get back home before dark. Most of the time you were breaking trail or following an unmarked trail cut through the bush or following ditch lines next to the highway. Racing was hugely popular with oval and cross country events happening every weekend. No matter where you lived in the snowbelt it was not uncommon to have a local winter carnival featuring a snowmobile race. As some of these events grew in stature, the factory race teams would show up to race against each other all in a bid to capture more sleds sales by taking checkered flags.
Competition in any form always improves the machinery and the people that compete. There is no hiding from the public when a manufacturer’s equipment is not competitive. “What Wins on Sunday sells on Monday” was first and foremost in many company boardrooms in the early 70’s. Engineering and race departments were flush with cash to build a winning sled that would be the template for future production models.
Photo: Tom Hammond
The big three sleds builders (Arctic Cat, Polaris and Ski-doo) had been battling each other since the mid 60’s. Each year would see one of the companies take home bragging rights as the winner of the most checkered flags. Ski-doo had the advantage early in the racing game with their exclusive Rotax engines. Polaris and Arctic Cat (and everyone else) were all sharing JLO, Sachs, Hirth and Kohler power. It became evident that to be successful, not only on the race track but in business, a single-source engine supplier was required.
Polaris would partner with Fuji Heavy Industries (Subaru) to build what were known as the Polaris Star Engines. Arctic Cat struck up a partnership with Kawasaki to supply engines. With exclusive engine contracts in hand, the race shop dynos were running overtime to improve their durability and performance.
1971 Arctic Cat EXT – Laboratory on Skis
In 1971 participation in stock and modified racing classes was growing by leaps and bounds. full-blown factory modified race sleds were available to qualified racers in 1971. The machines utilized free-air motors with expansion chambers available in sizes from 292cc to 800cc.
Team Arctic racers had two versions of their race-ready EXT; a short track version based on the successful 1970 Puma using a short (30” track length on the snow) steel cleated track that was 17” wide. Short track race sleds were all the rage in 1970 to reduce weight and create a machine that was easy to throw around on the short 3/8 mile banked oval tracks of the day. Racing had also revealed the advantages of a longer wheelbase and that is where the 1971 EXT Special came into action. This sled was built around a new 15” wide steel cleated track that was longer (40” of track on the snow) that wrapped around a narrow version of the famous Arctic slide rail suspension. Introduced on the 1968 Panther, Arctic Cat’s slide rail suspension was a proven performance advantage and industry benchmark at the time. The EXT Specials were built more for the new longer half-mile racetracks with flat corners as well as for cross-country racing. It’s common knowledge today that a longer wheel base has better high speed stability and also provides better flotation and ride when competing in cross country races. The new 15” x 117” cleated track would be a key component on the new ‘72 EXT performance sled. The King Kat triples also revealed two components that would be used on the new ‘72 EXT; the first jackshaft split the secondary and chaincase to improve drive train efficiency. Arctic also utilized a fiberglass belly pan to reduce weight on the King Kats. Arctic Cat was selling sleds as fast as they could make them. The engineering department was flush with cash and talent and put to good use designing the next generation EXT that would be loaded with new innovations.
1971 Polaris TX Racer – The Competition Cooler
Arctic Cat’s cousins to the north (Polaris) had just come off a winning season with an all new aluminum chassis TX racer. Going into the 1971 race season Polaris surprised many with a clean sheet of paper race sled that looked fast standing still.
The new TX racer was built on a 100% aluminum chassis, bulkhead and belly pan. A 15” cleated track wrapped around the “Power Slide” slide rail with twin shocks mounted on the rear arm. The fuel tank was center-mounted following Arctic’s lead with the 1970 Puma. The lowered engine position combined with moving the fuel tank from the rear of the tunnel to the center of the chassis was what we today call mass centralization. This sled also featured a crude (but effective) hydraulic disc brake using a cable actuated master cylinder. The new hood design and wedge seat wrapped in Polaris traditional colours (red, white and blue) was created by Al Schindel. The rest of the sled featured the exclusive Polaris Star free-air motors with cylinder heads peaking out the hood as well as that aluminum clutch!
The secret weapon lurking under the hood of the Polaris factory racers was that aluminum primary clutch. The forerunner of the current “P-85” flyweight clutch had roots going back to the late 60’s. Polaris race team member Leroy Lindblad took a real interest in the development of this clutch. His early work on weights and spring combinations was a game changer. The new Polaris Star engines were down on power but they were always explosive off the line and the engines seemed to get all of their power to the track. This had the competition scratching their heads for a few years while they played catch-up.
1972 EXT – The Most significant Arctic Cat of the 70’s
Photo: Cody Mckvicker
The snowmobile under development for the ‘72 race season in both stock and modified classes would turn out to be a chassis used in future El-Tigres, Lynx and the popular Jag series right up until 1981. The new chassis was wider than previous Arctic sleds at 33” compared to a standard 29” width. This change was dramatic when the sled was first seen on the snow. A 10 year production run tells you Arctic did an excellent job creating a leaf spring chassis that provided an outstanding return on investment (ROI) for the bean counters.
Photo: Ramond Estes Jr
Kawasaki Free Air Power
The new EXT featured Kawasaki free air engines in 245, 290, 339, 398 and 436cc free air twins. Three triples were also offered to compete in the 400, 440 and 650 mod classes. The EXT sleds were built with twin expansion chambers with silencers available to meet the current sound regulations. The carburetion used by Arctic surprisingly was twin Walbro WR-1 butterfly carbs. Mikuni round slide carbs would have to wait until the ’73 model year. The ignition on these first motors was still a magneto design on the 250-400 twins. CDI was used on the 440 twin and triples. Aside from the old school carburetion and ignition, these engines were very competitive.
Under the hood was a brand new Arctic primary clutch, cast aluminum chaincase and Kelsey Hayes hydraulic disc brake. Like many companies Arctic had been using Salsbury primary clutches. The Polaris primary had raised the bar in performance, tuning capability as well as reducing harmonics on crankshafts. Arctic hired an engineer outside of the snowmobile business (Keni Prasad) that designed a new primary that separated the ramp and the weight. The new design had the ramps mounted to the moveable sheave and the weights (roller arms) pivoting from the spider. Torque was transferred through round bushings that would be upgraded to hexagonal bushings for improved reliability. This Arctic primary would later be known as the Arctic Hex clutch, which Arctic sold to many other sled manufactures including Mercury for their Sno-Twisters. The clutch worked very well once the initial manufacturing issues were resolved.
The new aluminum chain case replaced the stamped steel unit used on previous Arctic race sleds. The new design ran cooler, improved torsional rigidity and (combined with a jackshaft mounted Arctic secondary) greatly improved belt life through better clutch alignment. The move to follow Polaris with hydraulic brakes would become a mainstay for future race sleds but oddly would not be used on a production sled until the Wilwood Hydraulic brakes used on the ZR’s in the 90’s.
Suspension: Something new, something old
Arctic introduced a new mono-leaf spring combined with a redesigned ski profile on the front end to improve control. The new steel skis had the edges turned down to improve bite into the snow and also deflect snow away from the driver’s eyes. The tapered mono-leaf springs replaced the multi leaf springs used by everyone else in the industry. This provided a more consistent spring rate and the hydraulic shocks dampened the travel.
The track suspension was the famed Arctic torsion spring suspension with a single shock on the rear arm to control damping. The Arctic suspension used torsion springs on the front and rear arm to control weight transfer and ski pressure. The EXT ran with a 15” steel cleated track with internal drive that engaged the track cleats. Crude by today’s standards the cleated track was used on race sleds for over a decade.
Styling: Great lines and curves
The ‘72 EXT was unlike any sled Arctic Cat had built before. Gone was the famed leopard skin seat treatment. The free air engine was now tucked inside a new hood design built to channel airflow through the hood and increase air velocity for improved cooling. The enclosed hood also prevented steam from snow and slush flashing off on the exposed cylinder heads of the ‘71 EXT design. The enclosed hood also allowed Arctic engineers to get a jump-start on containing noise on free air engines for the new sound regulations starting in 1975. The belly pan was also new featuring a deep V design to improve performance in deep snow and improve structural rigidity of the new fiberglass construction. The new sled was designed by legendary Arctic Cat designer Leon Raiter and fiberglass guru Kenny Halvorson. The design would become an Arctic Cat classic.
Controversy – USSA and Arctic agree to disagree
It was during a visit by USSA officials to Arctic that it was discovered new cylinders were being retrofitted to the engines supplied by Kawasaki for the ’71 race season. The Kawasaki motors Arctic had filed with the USSA as per the rules had their serial number filed and classed as modified for the 1971 race season. USSA was adamant that once an engine was filed as modified, it must remain that. Arctic Cat argued that the EXT specifications were filed prior to the Sept.1st deadline and ruled eligible for the stock-racing season. While the engines had been filed with USSA, Arctic argued they were not used due to issues with the chrome plated cylinder bores. The 1971 engine cranks were all 60mm stroke and were not changed for the ’72 model year. Kawasaki did supply new cylinders for the ‘72 EXT models with improved chrome plating. It was during the USSA visit it was learned the defective cylinders were being replaced on the registered cranks. USSA looked upon this update as “re-manufacturing” and issued a ban on all 1972 EXT sleds from stock racing just prior to the start of the race season. The result was a legal battle that eventually was resolved out of court between both parties. The USSA allowed the 250 and 400 EXT to compete in stock classes and the 290 and 340 would only be allowed to compete as modified race sleds.
The ‘72 EXT was built by Arctic in sufficient quantities to qualify for Stock A (0-250cc) and Stock D (346-400cc). While the standard EXT did not come with factory installed headlight and taillight a kit from the factory was this final touch to make these sleds stock legal.
Polaris ATX 335 – “A” stands for Aluminum
Al Schindel was tasked by to integrate his eye-catching ‘71 TX racer and adapt it for production (add headlights) for the new ‘72 ATX. The twin headlight styling with the cylinder heads exposed in the center of the gleaming white cowling with low cut blue tinted windshield was a significant departure from the boxy hood designs of past Polaris sleds. Polaris continued with the red, white and blue color scheme except the blue used in ‘72 was a new deep metallic blue. When these sleds were first revealed at snowmobile shows the red seat and white hood were familiar but the classic powder blue tunnel color was long gone. It took awhile to adjust to the new Polaris blue.
A big change for Polaris was the move to a center mounted fuel tank. The ‘72 ATX had a redesigned steel 5-gallon fuel tank positioned in the center of the sled. Ray Monsrud explained the reasoning behind the change; “We had been testing a variety of fuel tank locations over the years. Originally we built them like a suitcase where the tank was removable to fill and located on the right hand side of the sled under the hood. Then we moved them to the rear of the machine to counterbalance the weight of the engine up front. We soon found out that the rear tank worked like a pendulum when cornering fast making the rear end slide out from under you. The best spot was moving the tank in front of the rider near the sled’s center of gravity. The machine handled way better on the oval and when flying over road approaches.” The ‘72 ATX (and all Polaris production sleds going forward) had the center-mounted fuel tank.
Ray Monsrud was working as project lead on the ATX project to bring the sled into production. “We had a great team with Arlyn Saage, Bob Preskwas, Ed Monsrud, Jim Bernat and Burt Bassett on the development team. Back in those days, the factory race team guys like Eastman, Rugland and Lindblad would all give input. We put our heart and soul into the company to build a winning sled. We worked till the job got done before we went home.”
Arlyn Saage worked in Polaris Engineering for decades. He was a master fabricator and worked on the ‘72 ATX project as it was readied for production. “The ‘70 and ‘71 TX racers were the first aluminum sleds we built. We were new to welding aluminum so the originals were pretty crude. For the ‘72 ATX, I built a set of jigs to attach the tunnel and front bulkhead. I made two sets of jigs to assemble the bulkhead. We worked 24/7 building the jigs to ready the ATX for production. The aluminum was 5052 and was welded together by hand using a MIG welder. The front spindle brace was formed and then riveted into place to the all aluminum belly pan. When I look back at how we would ‘Flintstone’ those machines together, I am amazed at how good they turned out.”
The ATX chassis was very comparable in dimensions to the EXT with a 33” overall width and a length of close to 107”. The entire chassis was spray-painted and after a few short weeks the paint started to flake off the tunnel. “We were just learning how to prepare aluminum for painting and of course powder coating was not available to us like today.” The new ATX sleds were constantly being touched up to keep them looking sharp. Chrome skis and shocks were all the rage in the early 70’s and Polaris added that touch to the ATX racers. The chrome looked great for about a year and then started to rust once the chrome started to pit. Chrome skis were used again on the ‘73 TX and after that on a few Indy 600 SP models in the 80’s.
Photo: Tom Hammond
The new ATX was built in just two models; the ATX 335 to compete in Stock C (296-345cc) with its twin cylinder 335cc Polaris star engine and the TX 500 LTD with a 502cc triple (the first production triple). The 335 used the Polaratone two-into-one exhaust. Polaris was the first OEM to use Mikuni VM carburetors with fixed jets. This prevented the average consumer from tampering with the carbs and burning down engines, which was common with Tillotson carbs of the day where you could lean out the high-speed jet while screaming across the lake. Bob Przekwas worked and raced for Polaris for decades and tells us about the Mikuni carbs; “Originally we had them mounted solid to the intakes and found issues with engine vibration causing the engine to lean out. After some work on the dynos with Jerry Shank we discovered that a rubber adapter between the cylinder and the Mikuni isolated the carburetors from engine vibration. This was the cure for fuel foaming in the float bowl.” Polaris had all their production machines using Mikuni VM carbs, long before they became the industry standard.
The 335 cc twin also came standard with CDI ignition for improved combustion and starts. The piston port twin was not a world-beater when it came to HP (estimated at 32-35 hp). Polaris did have a trick they used to maximize power back in the day. The 335cc motor was equipped with twin 26mm Mikuni carbs. The smaller diameter carb venturi increased air velocity to better atomize the fuel as it entered the intake ports to maximize power and improve throttle response.
Aluminium Clutch – The Secret Weapon
The new aluminium clutch was called the Torque-O-Matic. Yes, the P-85 has roots going back to a Polaris patent (3,605,511) dated October 24, 1969. The new clutch design featured flyweights mounted to the moveable sheave working against rollers mounted to the spider. The spider transferred the engine torque through the moveable sheave via the buttons running in the spider tower. Designed over 50 years ago the flyweight clutch design is still in production. Today it is well understood but back in 1972 there were only a handful of people that understood the interaction between the weight mass, profiles and spring rate to optimize the clutch performance. People in the know had a distinct advantage on the racetrack. The new primary was mated with the old school steel torque sensing secondary mounted on a new cast aluminum chain case. The design of the new primary allowed it to respond much faster to the load on the secondary allowing for better back shifting and maintaining the engine in its power band.
The chaincase from the ‘71 racer had been retrofitted from a band brake to a hydraulic disc brake. The new 72 chaincase was now designed for an integrated hydraulic caliper and rotor. The handlebar mounted brake lever with integrated master cylinder was an in-house Polaris design used for decades before switching to Hayes brake systems used on today’s sleds.
Suspension/Track – The Power Slide
Polaris was now into their 4th season with their Power Slide track suspension heading into 1972. Polaris engineering and racing had already determined that a separate front torque arm and rear scissor arm offered more options to improve ride and handling. To reduce unsprung weight, Polaris used fiberglass rails to support the hyfax. The Polaris design had a separate front torque arm with torsion springs for support. The rear arm used two hydraulic shocks and twin torsion springs that could be adjusted to set their pretension much like today’s suspensions.
Ed Monsrud talks about the Power Slide design; “We started working with the front torque arm position to determine its effect on ski pressure. We did not have a limiter strap like on today’s sleds so we drilled holes in the tunnel to change the position. The fiberglass rail was also easy to work with and we would drill new holes to position the arm to increase spring tension. The two-position rear torsion spring allowed for quick changes to improve weight transfer. The Power Slide was crude by today’s standards but it worked and we won the Winnipeg to St. Paul back to back using it.” Polaris (like Arctic) ran a 15” wide steel cleated track but the ATX had an extra 5” of track on the snow compared to the EXT.
The Race Season – It’s Time!
For years the season opener was in International Falls, MN on the first weekend in December. The new EXTs were absent as the USSA had banned the sleds from stock racing. The new ATX only managed a 3rd place in Stock C.
After the USSA and Arctic agreed on the EXT controversy, the 250 Cats would dominate Stock A and Stock B all season long with points championships in all three divisions (East, Midwest and Western). In Stock C, the Polaris ATX had a stellar season with competition from the 250 EXT as well as some very fast Rupp Nitro machines. Polaris won season point championships in USSA East and West divisions. Stock D would see the EXT 400 pick up the USSA Central and Western points championship.
It should also be recognized that Dorothy Mercer (driving for the Polaris factory team) rode a modified version of the ATX to a 3rd place finish in the 1972 Winnipeg to St. Paul I-500 cross country race. This still ranks as the best finish by a woman in the history of the race.
The Race to Dealer Showrooms
The ‘72 EXT and ATX were all sellouts and everyone that missed out in 1972 couldn’t wait until the ‘73 versions came out. Arctic Cat introduced a more trail friendly version called the El-Tigre. It was available in four engine options from 250 to 440cc and featured a two-into-one exhaust for quieter operation, factory installed headlight, taillight and brake light. The same chassis would be used on the El-Tigre in 1974 and then would see duty on the popular Jag from 1975 until 1981.
The ATX did not have as long a production run as the EXT chassis. Polaris expanded the TX series in 1973 with a restyled hood, seat and dash. The TX was available in four engine options from 295 cc to a 432cc twin free air as well as the TX 500 LTD triple. The power slide suspension was replaced by new stamped steel, single shock on the rear arm suspension called the “Equiliberator”. It never was seen as an improvement over the Power Slide. On the race track the ‘73 TX was not as competitive as the ‘72 versions. The competition had caught up fast to the ATX 335 and Polaris really did not build a competitive stock racing sled until the 1978 RX-L 340. Where Polaris did do well is with the features that originated from the ‘72 ATX; aluminum flyweight clutch, hydraulic disc brakes, Mikuni carbs, CDI ignition and track suspensions that evolved from the original Power Slide.
Looking back to the winter of ‘72 I have very fond memories of traveling across Manitoba, northwestern Ontario and northern Minnesota with my dad racing our ‘72 ATX. We raced against the EXT’s, Nitro’s and TnT F/A that winter living the dream. We won some races and we lost some. The EXT was a dominant sled on the oval and the record books prove it. The ATX worked well on the racetrack, breaking trail or riding ditch lines. It was a great all around sled.
Author Hal Armstrong on his 1972 Polaris ATX that he and his father raced in 1972.
Racing is still the ultimate test bed to improve the sleds we ride. It was true 50 years ago and still is today. “Every time we race, you win!”
SnowTech thanks the following for their contributions to this article – Roger Skime, Ed Monsrud, Bob Przekwas, Jim Bernat, Arlyn Saage, Ray Monsrud, Dennis Paquet, Tom Hammond.