Boss Cat 0 - 1970 Boss Cat I - 1971 Boss Cat II - 1972
Boss Cat III - 1973 Boss Cat trailers Arctic Cat extras
The other guys Home Contact
Site map Guestbook

The EXT story


By Glen Mallory

Journey with us now to those thrilling days of yesteryear. When alcohol and ether fumes meant pulse pounding modified snowmobile racing and technology was advancing faster than the national debt. The purpose of this series of articles is to pay homage to the most recognized race sleds of that era, along with the occasional oddity. Over the next few months Arctic Cat’s 1970-73 EXT program will be examined and discussed at length, with an emphasis on model identification for collectors. In time, other brands of sleds will get their turn under the microscope, in this column. But for now, we are going to turn up the rock and roll and pound ourselves black and purple in a trip back through time.

It’s good to be king. To be on top and master of all you survey. But staying up there can be dangerously hard work. Picture yourself in Arctic Enterprises shoes about oh, say fall 1969. You have sunk the entire company’s fortune in one model of sled over the past three years, the Panther, and it has paid off nicely. You have an I-500 win and many other major race victories in your pocket. Sure you experimented with offshoots of the same platform to placate your critics. The 68 Cougar was a Panther with bogie wheels meant to show just how superior your slide rail suspension really was. You took the losses on that model in stride since you wisely chose not to make too many of them. The 69 Puma prototype has showed some promise in using the best features of the Panther and getting rid of the weight of the two man sled. But the competition has new engines, and you dallied too long getting a patent on the slider, so others will build their own versions. Your critical advantage is about to be overrun.

Well, when the flies invade the farmhouse, reach for a fly swatter. The EXT program was initiated as a major attempt at keeping a leg up on the competition and keeping Arctic Cat in the winner’s circle. "Fly swatting" was exactly what Arctic Enterprises had in mind. Consider what the acronym "EXT" means: Exterminator. This nickname comes up time and again in old service bulletins and I remember it well from our family’s dealer days. The way Cat made sure the letters were graphically displayed as nastily as possible across the back snowflap on the sleds that carried the name from 70-73 just screamed B-B-B-Bad. The unmuffled tuned pipes on these sleds just served to emphasize the point: "This ain’t your grandpa’s P12K anymore."

At first, the name just meant a modification package similar in concept to Chevrolet’s famed Z-28 muscle car. Take a stock sled and stick bigger or more carburetors on it. Add in available expansion chambers and even trick items like all aluminum bulkheads, ported cylinders, free air conversions and racing clutches. Go jump on the lake and "beat thy neighbor."

The 1970 model hot sleds can be divided into two groups: The MOD sleds and the EXT sleds. A 1970 with a MOD designation means the engine modifications were carried out at the factory with little or no help from the engine manufacturer. This was a continuation of the work being carried out by Shorty Long and company for most of the Arctic racers from the beginning. An EXT designation means the engine mods were done by the engine manufacturer to Arctic Cat specifications. To further muddle up the issue of model ID is the fact that, racers being racers no matter what time it was, quite often MOD motors were stuck in trick chassis with EXT parts and visa versa. Consider these machines to be mostly hand built exotics and in relatively small quantities. Some were even prototypes of what would be sold for trail use the next season.


Consult Illustration 1, 1970 model line up chart:






292 H MOD





292 A EXT





295 J EXT






340 J EXT






340 S EXT





340 H MOD





340 H EXT





399 K MOD





399 K EXT





440 H MOD



211 R


634 H MOD





760 J MOD





793 H MOD






Both Panthers and Pumas got the MOD/EXT treatment for the 1970 model year. By far the Panther EXT’s are rarer than the Puma EXT’s as much more emphasis was poured into the little sled. Mountain racers and hill climbers got the lions share of the Panther MOD/EXT’s as the big sleds long track was an asset in deep snow. Some of these sleds had optional special cut down hoods made to take advantage of free air conversions. This would be a foreshadowing of what was to come for 1971. Almost all engines from all manufactures got the MOD/EXT treatment for the 1970 season as Arctic was trying to shake out the most horsepower and choose the best engine manufacturer as it’s sole supplier for coming years. Dealers were bitterly complaining over having to carry parts for Hirth, JLO, Kohler 2 stroke and 4 stroke, Sachs, Sachs-Wankel, and Kawasaki. Add into this Cat’s attempt at building a minibike for off-season sales and its no wonder some dealers refused to carry the minicycles. They just did not have room to carry the inventory!

To identify a 1970 MOD or EXT, you must either look for clues or find the model plate if it is still on the machine. The latter is obviously the easiest choice. Take a 1970 340 Hirth single powered MOD Puma for instance. Its model code is 340HM with "H" for Hirth and "M" for MOD. A 1970 292 Kawasaki Puma EXT would have the code 292AEXT. "A" meaning "Arctic", which is what Cat called their captive brand of Kawasaki engines from 1970-75.  Other engine codes seen to date are "K" for Kohler, "J" for JLO, "S" for Sachs. (Of course the engine code I am leaving out here is "W" for Wankel, but they never officially built any rotary powered racers so that does not apply here.) For the Panther sleds, the abbreviations are all the same. In some cases you may find a "P or even more seldom a "PU" on the Puma models.

If the model plate is gone, then things get tougher. Look for trick items like an aluminum bulkhead on the Puma chassis. These were used on most "MODS" as a way of cutting off about 16 pounds of dead weight. Some EXT’s may also have had them. Other tricks to look for are the small white EXT decals next to the cc decals on the hood used on the 1970 sleds. You can also look for oversize carbs or dual carbs on an engine that normally would only have one. Polished or oversized ports, altered hoods, free air conversions, factory tuned pipes are another tip. But also remember that all these same parts were also offered over the counter as replacement hop up parts. So just because it has hot parts on it does not guarantee that it is one of the sleds in question. For a premium example of a 1970 Puma MOD, visit the VSCA’s museum website at There is a beautifully restored 634 FA Hirth powered sled there. Also remember that real people stamped these model ID plates, and sometimes the numbers and letters got switched around in order. However, the basic rules mentioned here should still apply.





Prototype version, 1971. Notice how the EXT (Hirth) engine is mounted almost straight up and down.


For the 1971 model year, the MOD program was cut back to just a few models. The 340 Hirth Mod single soldiered on in both the Panther and Puma and so did the 634 Hirth Mod and a new modified 440 Kawasaki Fan cooled twin. Of definite collector interest are also the 292/340/399/440 fan cooled Z mod Kawasaki powered Pumas. These "super stock" sleds are so rare, that they are unknown to many Cat fans and this writer has never seen one up close. I have been able to figure out a few things about these engines from talking with lucky owners as well as extensive digging through moldy parts manuals. They made about 100 sleds each of the 292, 340, 399 engine sizes. The 440 FC Z’s production figures are less clear. Estimates range between 100 and 500 of these sleds and actual numbers may have been mixed in with the 440 Mod Puma production numbers. What is clear is that the engines were made with an extra impulse fitting for a dual carburetor setup, but often the second carburetor was not installed at the factory. Some may have had expansion chambers. Most probably had the stock can muffler. Internally they had porting and compression that were quite similar to a 71 EXT Free Air engine. This means that these engines respond very well to most common engine mods, and I know of two installations where they outperformed the free air engines they replaced. If an engine is found, it will have a designation like "T1A Z " then the engine displacement and the rest of the serial number. The number will be on the top right fan housing if the engine plate is missing. These engines look exactly like a mild trail T1A FC motor. Several of these engines have been found mixed in with stock T1A’s, so next time you’re at a swap meet and you see a bunch of old Kawasaki Arctic Cat engines for sale, take the time to read the serial number. You might get a surprise. A complete Puma would have the designation PU (cc size) AZ or PU (cc size) AZMOD or similar. With the flurry of success of the Free Air EXT program and the USSA’s growing minimum build requirements, this promising engine wound up on the back burner and was quickly forgotten.

The 1971 EXT program gave birth to four distinct models of EXT. The most common being the regular Puma tunnel based 292,340,399,440 T1A-FA model, high compression, Free Air Kawasaki twins. This sled shared its track and suspension with the sports model Puma, which had a shortened version of the Panther’s 17-inch wide track and skid frame. A late introduction was the EXT Special model which had a tunnel extension grafted on the rear, an aluminum bulkhead, a more modern looking seat that did away with the plastic tool box and rear fascia found on the regular EXT and trail Puma, and a longer, narrower 15 inch wide track and a longer skid frame. (Several features from this sled would later find their way onto the new for 72 Cheetah trail sports model.) The longer narrower track was intended as a way to improve handling on the new ice oval race tracks that were to become the dominant form of racing in this era. The Special shared engines with the regular EXT. Both of these sleds feature tilted forward engine mounts as a way of lowering the center of gravity. Interestingly if you look at the early 1971 model advertisements and even at the 399 EXT pictured in the famous Cat epic "Legend", the engine is mounted straight up and down. These are obviously pre-production prototypes and this idea was a last minute change to the line. Both sleds came with a choice of exhaust systems. You could have the stock can muffler, the two into one expansion chamber or a set of two complete expansion chambers that exited just under your TOES! This made for warm feet on long rides or races. The twin pipes are the famous "crossover" pipes. So nicknamed because the left side exits under your right foot and visa-versa. No silencers were included as these were meant to be race sleds only. Most engines were breaker point ignition except for the 440cc version with CDI. All were single spark plug heads and either had dual Tillotson HR or Walbro WR carburetors, 7.5/1 compression ratio, and Salisbury "R" series competition drive clutches.

To identify a 71 EXT, look for the letters "AE" then engine size in the model plate. The Special can be identified by the letters "AES", and then the engine size on the model plate. Also if the plate is missing, the Special does not have the Puma style toolbox on the back and the seat resembles a more modern El-Tigre in style. Both had the flashy galvanized skis and chrome shocks on the front. Both had the chrome plated gas tank with lightning bolts on top.


1971 EXT SPECIAL 340.


The next two sleds in the EXT line are a study in contrasts. One is an oddball that has been forgotten and may very well have been either a special order sled or just a neat way of using leftover parts, the other is a legend that was so damn fast it helped get the 800cc class banned. The first is the 1971 399cc Panther EXT. They made 50 of them. That’s right. Near as I can tell it was the 399 FA EXT engine and hood combo slapped onto a Panther chassis. No one whom I asked has ever seen one of these sleds and the reasons why they built them are lost to time. So I am not going to linger on this one. On to the King Kat!

1971 399 Panther EXT




The King only reigned for one year, but what a year it was. With a chassis that shared parts with the EXT Special, and the big bore Panthers, and had many all it’s own. The King had a steel bulkhead and jackshaft drive to handle the power of the big cc motors. They also had an in between length version of the 17 inch track that would later appear in mass quantities on 72 Cheetahs. This track was longer than the stock Puma’s and shorter than the Panther’s.

The smallest King Kat was the 650 JLO triple version. They made about 112 of these, give or take a few. Featuring three big WD or HD model carbs and tuned pipes all around, this sled just sounds like thunder when it is fired up. The most popular King Kat made, at a whopping 174 copies, was the 793cc Hirth Honker triple. So dubbed for the bionic goose sound it made when all three big HD carbs were opened up on that 80hp triple. My father sold one of these to a local racer back in the fall of 70. The sled ran an honest 85-90 mph on good days. Back then, that was incredible. What was more incredible was the pain endured while trying to keep all three of those fussy big Tillotsons synchronized. These were the days when Mikuni VM carbs were still a dream to most sledders, and my father, to this day, does not regret the passing of the Tillotson era. Of course the sled that really sticks in the minds of Cat fans everywhere is the first true production four cylinder modern sled, The 798cc Kawasaki powered four cylinder model T2A800F Free Air Four Cylinder racer. This sled was laughingly rated at 85hp on pump gas. It was capable of much more. This sled was introduced with much fan fair to dealers as the very definition of "High Performance" with a whispered top speed, during pre production testing, of 103 mph. It had four 44mm Mikuni butterfly style carbs and four expansion chambers. Two pipes exited at the front and two exited at the side. When idling, this sled sounds like some sort of odd pro-rally racecar. They made about 124 of these and these are the sleds that are now selling for upwards of 7500 dollars restored. The sled had some serious problems. With that massive 35 pound 11R Salisbury drive clutch kicking in at high rpm on a crank with no counterbalance, crankshaft and even complete crankcase failures were more common than not.

The torque produced by that four is quite capable of ripping the Panther derived drive cogs apart. Also like many big bore air-cooled multys, the center cylinders had a tendency during long races of cooking themselves. When these sleds were introduced, Kevlar drive belts did not exist. Thus drive belts were being fried after four lap heats! They handled like bulls in a china shop and with the power on they wanted to plow straight ahead, so accidents were common. The sad part is those accidents were now happening at speeds in the high 90’s, so people were starting to get seriously hurt. The ruling race body of the day, USSA, did not like this sled at all. At it’s first race they halted competition and demanded to know if Arctic Enterprises had built enough of the fours to qualify them as stock sleds. Arctic had built enough, just enough. But after the close of the 71 season the USSA announced that the 800 class was going to be phased out and not return for 1972. So in a way the big Cat was stillborn and never debugged enough to get all the power to the ground. A friend of my brothers picked one up used around 1973 and kept the sled for several years. He massaged the "outlaw " sled into a triple digit, grudge match, drag racer that was unbeaten for a long time. So the speed potential was definitely there. It was just the sleds finicky behavior that kept it from being realized. Frustrated by the fours potential to eat itself, many King Kat racers asked for and got 793 Hirth and 650 JLO replacement engines to continue the rest of the 70-71 season on. How many triple King Kats at shows today are really old four bangers in disguise? We’ll never know. But a check of the codes might help. The model codes are KK800A, for fours, KK800H for Hirth triple, KK650J for 650 triple JLO.

The stock EXT’s handled better than their Panther ancestors, but there was clearly room for improvement. The center of gravity needed to be lower, the ski stance wider, the two cylinder engines needed more power and better clutching to stay competitive for another year. For 1972, all these problems would be addressed in a sled that would later be changed into a name that would become synonymous with speed. See you again next issue.



The EXT story



In episode one on the Arctic EXT program, we covered the first two years in the development of the lithe little race sleds and the heavy weight hitters, the King Kats, for the big cc classes. Now it is summer 1971. The King Kat has been deposed through rules changes. "The King is dead. LONG LIVE THE KING!" The only trace of any 1972 model development on the King to ever see the light of day are a few part numbers for covers and accessories released to dealers for the April 1971 accessories catalog. However the track and suspension developed for the King will live on in more than 15,000 1972 model Cheetahs being produced for trail use. The 1972 Cheetah combines the underside of the King Kat with the front frame, hood, toolbox and tank of the Puma. The longer sport sled is built mainly to answer the complaints of taller riders about riding with your knees in your face, and the sometime squirrel like handling of the Puma chassis. A Cheetah SS model is briefly considered, but it is never built. Alas, the sled will not have the big inch motors. They are gone for good. Instead the Cheetah will stick to the tried and true T1A model Kawasaki fan cooled twins. Arctic’s pet brand of engines is now the only brand used in 90% of their production. The big Hirths and JLO’s die right along with the King and inventory weary dealers breath a sigh of relief everywhere. The only non Kawasaki engines used this year are a few 8hp Kohler four strokes and 10,000 303 Sachs Wankel engines stuffed into Panthers due to popular demand. Rental people love the Kohler thumpers slow speed and reliability and the farmers and backwoodsmen love the Rotaries ability to climb ridiculously steep hills. Further indicating that most of the fast square pan Cats are gone is the death of the MOD program. No MODS are built for the 1972 model year. So just where has AE been pouring all their money into for the coming race season?

THE 1971.5 292 TURF TIGER


The sled that is a sort of 1971 _ model is the Turf Tiger. An obvious amalgamation of parts thrown together to put Cat in the winner circle in grass drags. It has a 1971 EXT hood, tank, pan, and bars. It used 1972 style monoleaf narrow skis, with no shock mount, that were often replaced with wheeled skis that resemble roller blades. The most striking thing about it is the wheeled suspension. That’s right! Other than the Kitty Kat and the 68 Cougar, and the ultra rare para rail style 72 polytrack Panther, this makes it the only other black Cat with a version of bogies. Obviously to make it run faster on grass. Along with the wheeled rear end is a poly track, which would be no surprise to any die hard grass racer. The seats were long and thin. Most serious grass racers replaced them with 72 Kitty Kat seats as a way of cutting weight. I would not be surprised if the tank was ditched along the way as well, as you really did not need four gallons of gas for a 1/8 mile run. The engines in these were 71 EXT FA twins in 292,340 and 440 cc displacements. They featured dual Walbro WD carbs and dual crossover pipes like the full race 71 EXT’s. These sleds were never meant to see snow, or turn well for that matter. That’s why you will seldom see one with shocks on the skis. More unwanted dead weight. Other creature comforts, like foot rests and a headlight, were not installed at the factory as well. As you might expect, they did not make very many of this specialized dragster and estimates run from 50 to a little over 100 of each engine size being made. The sled was often heavily customized and engines were changed over to more modern versions as owners raced the machine through the mid 70’s. So finding a nice original one is like finding the Holy Grail. Most people do not realize that these are rarer than the much-hyped King Kats, and the little sleds often get confused for a 71 EXT, when the hulk of one is found. One way to tell the difference is look for the letters "TT" in the model code, vs. "AE" or "AES" for 71 EXT. The sleds were built during the summer of 1971, so some may call it a 71 model and the parts manual I have lists it as a 71, and they were no doubt raced that summer and fall. But my production figures list the sled under 1972. That’s why I like to call it a 71 _, since it was a sled that was being built just as the 1972 EXT development was hitting the production stage.

1972 EXT 440 TRIPLE.


The importance of the 1972 EXT in the history of Arctic Cat can not be over stressed.

This seminal model was to give birth to a whole new line of sleds for Cat and one of the longest running basic chassis in Arctic history. The first with the "V" shaped fiberglass pan. The long "laser style" pink stripes that were put on 73-75 Panthers and Cheetahs. The monoleaf front springs and the long and narrow 15 inch, cleated track, are also features that would show up again and again throughout Cats of the 70’s. This chassis can be traced right up from 1972 to 1981 through the early El-Tigres right into the 1975 Lynx and the 1975-1981 Jag. Sure, they made changes here and there, but the basic frame stayed awfully close to the 1972 model dimensions. The 1975 Lynx being the most radical variation in body work, with the pan being all aluminum. This chassis was light and a born handler. If you had to compare it to a car, I’d compare it to a Mazda Miata. You can fling this chassis into corners at speed, use your weight to balance it, and come out right side up. This was not a sled for riders who just like to sit still and drive. This was a R A C E sled with almost nothing in common with the previous Panther mutations. Of course, the trail sleds that descended from it usually had milder motors.

Speaking of engines, with the death of the King Kat came the opportunity to stick an 85+ horsepower 650cc triple in the EXT to fill a need to race in the remaining big bore class. There was also a 440 triple to be had, and rumors persist that some sleds were built with 400cc triples, as well. My production figures only give data on 650 and 440 triples, but I have a parts manual that gives the parts numbers for the 400 triple, as well as an old price sheet for complete engines. So were any built? All I can say is definitely maybe. The engines were modular in design. So you could take a 440 triple and make it a 650 just by slapping the 650 jugs on, or you could replace the entire engine rather easily. The downside to racing a 400 triple would be that some race associations of the day would have made you run in the mod classes or put you up in the 440 class, where you would most likely suffer a major butt kicking. So the demand for 400 trips must have not been strong enough to rate a historical note. 400 Triple numbers in the chart below are based on best guesses.






































Less than 25?














The racing twins were made in 250,290,340,399, and 440 sizes. Of interest and confusion is the fact that many three cylinder and two cylinder parts will interchange for this model year. The 440 triple is really three 290 jugs and the 650 triple is really three 440 twin jugs.

The outside jugs of a triple will replace the jugs on a twin. The center jug and head on a triple is specially made to fit there. The fins are cut down on the sides so it may go between the outside cylinders. The oddball/rumored/might have built/ 400 triple shares only it’s crankcase and related items with the other triples. The entire top end is unique. On all engines, dual/triple carbs and pipes were standard and only basic snuffers are included as silencers. The stock original carb was the Walbro WR-1 butterfly and the stock clutch was the Arctic round shaft racing clutch. This grand daddy of Arctic drive clutches was fairly successful in the 1972 racing season. Later versions on 1973 model trail sleds would cost the company dearly in recalls and premature failures and lead to the development of the classic Hex shaft drive. Racers who raced the 72’s into the 73 and later seasons often converted over to the Hex and Mikuni VM carbs, through a factory sponsored update program. Only the 440 twin and all the triples had CDI ignition stock. All the rest were point. That same update program also came out with a kit to adapt the 74 "C" series El-Tigre engine CDI unit to the single plug EXT twins, so you may find one of the smaller sleds with CDI today. Hydraulic disc brakes were rapidly phased in during production of the sled.

1972 EXT 440 Triple powerplant.


In conclusion, the 1972 EXT was probably the most important Cat ever built. It propelled the entire industry into a new era of long low and lean sleds that handled far better than their slab sided predecessors. The sled overcame a controversial USSA ruling against it and became the dominant force in stock oval racing from 1972-74 through updates and it’s El-Tigre descendants.

For 1973, a whole new line of engines would be introduced that would become another chapter in the "Legend." See you next issue for the conclusion of the "EXT" story.


The EXT story



1973 Models and 1974 Rumors.


After an incredible 1972, racing season that saw Arctic Cat EXT’s dominate most of the stock classes, 1973 was a year of changes at Arctic Enterprises. Some were good, some bad. The good news was that Arctic would respond to the complaints of EXT racers and make the 73’s lighter through the use of aluminum bulkheads throughout the EXT line, as well as making the body of a thinner gauge of aluminum. The entire sled would be a little shorter, lower, and wider. Aluminum bulkheads had been used on some 72 EXT’s, but now all would have the 16-pound lighter front parts. To keep the thinner tunnel from wrinkling like a beer can, extra ribs were stamped into the tub during forming.

Meanwhile, the 1972 style EXT soldiered on slightly detuned, under a new name, "El-Tigre". This was to be the race sled for the trail and to be the beginning of a name that would enjoy a run almost as long as the Panther.

Of course the big news for both of the high performance sleds was under the hood. The pure race EXT was to come in 340 and 440 twins and a 650 Triple. The fast but slightly heavier baby triples of the 1972 model year were discontinued. For the 250 and 295 cc classes, you had a choice of either racing the 250/290 El-Tigre or racing your 72 EXT with updated engine parts and tips passed on through the "EXT NEWSLETTER." You also could race the new Formula II 295 all alloy "Ugly Sled." More on that later. But the real story was the twin plug, free air, and Mikuni carbed engines used in the new EXT’s, FII, and the bigger 400 and 440 Tigers that year. These are coded "T7". (The "T8" 650 triple is basically a "T7" 440 twin with an extra cylinder grafted on.) The EXT/FII engines all had one Carb and tuned pipe for each cylinder, standard. The detuned El-Tigre featured the fat "pulse charger" 2 into 1 silenced exhaust.

For the first time, CDI ignition was installed on all engines. The output of these engines was very good for the time and is still impressive even today. We are talking open-air cooled motors here. No H20 pumps or any fans to keep it all cool or to suck away power. When was the last time you heard of a 440cc air-cooled mill putting out 70+ hp stock? The 340 was only ten horses behind. The 650 triple was rated in the owner’s manual at 100+ hp. If you grafted on the midseason update kit you were talking well over that. I have heard of these engines putting out 130hp when tuned on a knife’s edge.

Of course all that power came at a price: Reliability. To today's uninitiated riders, tuning a high performance free air motor is a lot like trying to build a wild cat caliber-hunting rifle. Tune it right and you can kill a grizzly with one shot. Tune it wrong and you have a pretty hand grenade. This explains why, if you took the time to fill out the EXT owners questionnaire in the owners manual and send it in to the factory, you got a free set of jugs in the parts kit that Arctic sent along to every registered racer. They fully expected you to blow a cylinder or two in a season of "heated" competition. That was part of the learning curve and all part of the cost of building race sleds. Remember that "cost thing", we will come back to it later, too.

1973 El-Tigre owners did not get all the freebies that EXT owners did. It was a trail sled after all and was meant to be more reliable. As such the key differences between a 73 El-Tigre and its predecessor, the 72 EXT, are that the Tiger has only one pipe and it is heavily silenced, and the engines tend to be in an overall milder state of tune. The smaller Tigers came with a CDI converted version of the 72 EXT single plug engine called the "B" series. Of course, to improve the sleds performance, all that was usually required was some creative Tiger/EXT parts exchanging. This worked both ways, I might add. By now, most 1972 EXT’s still running had been switched over to Mikunis from the lesser Walbro WR carbs, thanks to Cat’s extensive support program. The 73 El-Tigre also has a few other minor tweaks that one would expect in converting a racing design over to a trail sled, all to make it more "domesticated."

In the clutching department, Cat’s experimental round shaft racing clutch, first tried on the 72 EXT, was adopted across the board. Almost all 1973 Cats came with some version of this clutch. The exceptions are the Puma and Lynx. This decision would come back to haunt Cat for the next two model years and put the company deep into the red. The clutch that was proven an innovation on racers would not hold up under the heat and stress of an enclosed hood and typical trail rider spotty maintenance. A massive fix and update program was launched as Cat first tried to fix the roundy’s flaws, then later replaced it with the improved Hex shaft clutch. What this means for today’s collector is that finding one of these sleds with the original clutch on it is a real challenge and a big plus in the machines value at resale, if you intend to display it. If you really just want to race it in the vintage events, then you are far better off with a rebuilt hex shaft as parts are STILL out there for the thousands of these clutches used since 1974.

The Formula II was created out of a quest for absolute lightweight. No tie rods were used. They have a unique system of aircraft cable steering. Magnesium was used extensively throughout the sled, including the skis. The tunnel was a basic 73 EXT tunnel altered for even more weight loss. The engine was a unique 295cc twin plugged, carbed, and piped Free Air Kawasaki, that put out an estimated 50 hp. Not bad when the average 300cc trail twin was still 20 hp.

This is not to say that other EXT engines did not find their way into the FII chassis. Since the crankcase was the same on all the twins, a 440cc FII was just a top end swap away. Of course someone had to go one better and stuff the 650 T8 Triple in a few. These are a real rare find today and although not truly factory production, they still hold their value rather well. As for the body, or the lack thereof, the sleds came with a shrink wrap style fiberglass front-end cover. It was in two pieces and just covered the necessary bits to protect the driver. The engine was almost entirely exposed ala’ the 1971 EXT or Sno-Jet Thunderjet. Cooler motors mean more speed. The seat was small and thin, but white leopard skinned. Front shocks were not common, as they added a few pounds. Some may have been adapted to the sleds later, in a search for better handling. Since they were loosely based on the EXT, they could use any of the four alternative racing tracks developed for that sled. The competition manual from 1973 describes these. Some were involute drive, some were the older style cleat drive and all featured some combination of cleats and or rubber logo grips.

Of course, you could also go "deep pockets" and convert over to titanium cleats.

A smart racer would have several tracks prestudded according to the factory guide to get the best grip and get ahead of changing track and weather conditions. This way you could do a quick track swap rather than stand there for hours guessing the stud pattern that was the best. As for the number of FII’s produced, there seems to be some contention about that. A good friend of mine has chassis number 174, and he has talked with the owner of chassis number 175. So I’ll stand behind the "200" estimate shown below.












EXT 340




EXT 440




EXT 650










T1B290RS (?)














* El-Tigre models included for comparison purposes.

? There is some debate as to whether the 290 model was produced for 73. This is what I have researched so far.

I would consider this sled to be like the 72 400cc triple EXT: Probably made, but in numbers too small to justify much notoriety or surviving details. They may very well have been a pilot build for the 1974 model year.


In the end, the proof is in the race results. For the 1973 EXT overall, it was a pretty good season and Cat got it’s fair share of race victories. On the trail and cross country circuit, the El-Tigre showed well and often ran right alongside the updated leftover 72 EXT’s. For the Formula II, Cat again clashed heads with the USSA sanctioning body, which responded to the lithe sleds potential by creating a minimum weight limit that made the sled fall in line with the rest of the racers. USSA also began making more noises about raising the minimum build requirements for future "special" race sleds as a way of leveling the playing field. Teeth were gnashed in Thief River Falls, but things at the home front soon put the arguments on the back burner. Dealers were chanting some new, nasty words to distributors and the factory: Words like Carryover; Recall; Defect; Low-snow-level.

In the rush to totally overhaul the entire Cat lineup and bring it into the mid 70’s, perhaps some things had been overlooked. Market predictions were saying the company could afford to make 100,000 sleds a year at least until 1975. There was no end in sight for the demand. The truth was that around 1973 the bottom was dropping out of the market and sled makers were dying like flies in winter. They dumped loads of excess product on the market and then sold it for a penny a pound. Add into this the clutch, carburation troubles and the original engineering cost of the first Cats to meet the new for 1973 Sound Regulations and the cost of an expensive racer support program, and you have a company swimming in a sea of sharks. One more bite and it’s all over.

The bite came with the Arab oil embargo. This turned racing upside down and snowmobiling in general was taking a real grilling over being a waste of fuel.



1973 EXT 650.


All development on the 74 EXT’s stopped dead. The name would pass into history and not be used again ever on a true racing Cat. The F-II project torch would be carried on by a few of the factory tuners for the 74 season, as a side hobby. The sleds were raced by these people more to prove the point that the original concept was sound, than to sell sleds. They actually won at least two major races in the 295 and 340 classes with massaged 73 Formula II’s in 74. As for the 73 EXT, it soldered on for the 74 season, courtesy of an update program, but often minus its aluminum front end. Seems the trick front bulkhead ski "axle" or front cross member had a nasty habit of breaking in two with age, ski spreaders and abuse. At this very vulnerable point in Cat’s life, they could not afford a liability suit, so the sleds were recalled and owners were pressured to adapt the steel El-Tigre bulkhead to the racers. With the USSA setting minimum weight for all classes at a level that negated the reason behind the parts, it was not worth replacement costs.

So the reality of the 1974 season was a shortened race schedule and recycled 1973 race machinery for several classes. The 74 El-Tigre 295 and 400 were the two bright spots in the cross-country and pure stock racer classes though. These sleds came through with some "borrowed EXT blood" in them and brightened up an otherwise dull year. In a way, this was a peek at things to come for 1975 with race sleds heavily based on less expensive production machinery. But what might have been had not both the embargo happened and Cat got into red ink? What if the Formula II had not been regulated out? What might the 1974 EXT’s been like? Over the years, the rumor mill has spread folk tales of EXT chassis with Sno-Pro style, water cooled Kawasaki engines and unique front and rear suspensions being considered for 1974. In truth, to figure out what the 74 EXT’s might have been like just take a look at the 1975 Z. Imagine it shorter and lighter, more open hooded, same width, or wider, maybe with magnesium skis and skid frame. The engines would still be the familiar T7 FA’s. Cat had a bias against water cooling for "stock" sleds in the early 70s. They disliked the extra weight and complexity. Besides, the 1975 Z was a very competitive sled using just an improved version of the old EXT motor. So I think the 74 EXT’s would have been part 75Z, part FII, and all out Cat. But go to a vintage show soon and enjoy these leopard-skinned racers for what they still are: Loud, wild, fast, and not your Dads P12K.

For more detailed information, you can contact me at

Copyright 4/15/99, by Glen S. Mallory

RD1 Box 1585, Osceola, PA 16942.


Web design by Stephen Knox