1974 Rupp 3rd Dimension 1974 Rupp 3rd Dimension
Rupp Racers Take on SnoPro Ironwood Michigan, December 9th 1973 is a day that will live on in snowmobile racing folklore. This date is... 1974 Rupp 3rd Dimension

Rupp Racers Take on SnoPro

Ironwood Michigan, December 9th 1973 is a day that will live on in snowmobile racing folklore. This date is when a new breed of no holds barred racing snowmobiles from the best brains in the industry would be revealed. The race series was called SnoPro.

What was SnoPro? This was to be the pinnacle of snowmobile racing. Under the new guidelines, factory racers registered as professionals competed only against other registered professionals in three classes (340, 440, 650). Among the most exciting possibilities opened by the SnoPro class was with the machines themselves, where virtually unlimited modifications and experimentation was allowed. The only restrictions were pump gas only, no superchargers or turbo chargers and the physical size of the sleds. Weight was set at 250 lbs. minimum and 500 lbs. maximum. Overall length was set between 72”-120” and maximum sled width of 45”. The combined track width was set at 15”. There were no stipulations on machine configuration, engine placement, drive system, etc.

1974 Rupp 3rd Dimension

When the machinery was unveiled, race fans were not disappointed. The majority of the sleds looked conventional featuring new styling, liquid cooled engines, lots of magnesium and titanium and new suspension designs. The pro racers were like movie stars when they arrived in their new race leathers and matching helmets. The SnoPro concept was to allow the factory race team to compete against each other and allow the independent racers a chance to compete against themselves.

The rules for SnoPro had been established after the close of the 1973 season and work began on new race sleds that were to showcase a manufacturer’s engineering capability. The payback for the winner was to gain market. How big was the market? In 1973 alone, 450,000 sleds were sold globally. Winning on the track meant grabbing a bigger slice of that volume.

New Owners and New Direction for Rupp

While snowmobile sales were almost 4x the volume sold today there were thirty (30) manufacturers competing for market share.

Gene Bloom Rupp
Gene Bloom

Rupp was a veteran in the industry since 1963 but had recently gone through some rough times and had been sold to new owners in April 1973. Known for building performance sleds like the Nitro and Magnum models in the past, the new owner (Joseph Hrudka, owner of Mr. Gasket Company) was no stranger to performance and committed Rupp to compete in the SnoPro series with a low budget race team. That team consisted of Hall of Fame racer Gene Bloom and his brother in-law Tedd Pierce who was the mechanic/self trained engineer. These two would work day and night building three new race sleds from the ground up in three months to be ready for Ironwood. With the limited rules established, Gene Bloom was on a mission to improve upon his ‘73 Magnum race sled that he had limited success with. In his words,” I really expect this year to be better than last. We just didn’t have the time to prepare the factory Magnum properly.” Those words would come back to haunt Gene and Tedd as the late arrival of the new Kohler RS race engines resulted in less dyno time at R&D to figure out jetting and expansion chamber design.

With new ownership at the helm of Rupp, a new manager of styling (Denny Lutz) and manager of fiberglass (Dave Lutz) came on board and helped Gene and Tedd with new body styling that was lower, wider and more modern looking than the Magnum.

The concept was shown to Rupp management. I asked Tedd Pierce where the name “3rd Dimension” originated. “I wanted a name to stand out. I wanted to call it the 4th dimension. The 4th dimension according to Einstein is Time. This race sled was designed to minimize time going around a racetrack and make fast work of beating the competition. Management liked the idea of calling the new sled the “3rd Dimension” with the thought being that for 1975 a new race sled would be called the 4th Dimension. Tedd recalls, “The boss preferred 3rd Dimension so who were we to argue?”
The name was unique and the team ran with it.

Tedd Pierce Rupp
Tedd Pierce

How to Build a SnoPro Chassis on a Limited Budget

In looking at the majority of SnoPro race sleds from the ‘74 season the teams all were thinking the same – high power to weight ratio. Tedd and Gene chose to fabricate the chassis from magnesium, which is lighter and has a higher strength to weight ratio than aluminium. Anyone who has worked with this metal knows that this material is not easy to work with. The trick to bending and forming magnesium is to heat the material to over 500F to form it. The welding department at Rupp figured out a trick to heat just the area that was to be bent to form the tunnel and it worked. The new tunnel was made using the tooling for the ‘73 Magnum, but the new front bulkhead which used a triangulated front cross member to locate the spindles and improve rigidity when cornering at high speeds was unique on the new race sled.

Rupp 1974 3rd Dimension
Photo Credit: Ed Chestney

Tedd explained the new front end. “The front end was based on a modification for the Magnum that I had designed in the later part of ‘73. I had built in an offset on the left ski to get to increase ski stance. The new ’74 race chassis right hand spindle had 5 degrees more negative camber than the left spindle. When racing on an oval, the sled is always turning left. This means the right ski is always on the outside of a turn, so Tedd took a page from stock car design and increased the negative camber on the RH spindle. Increasing the negative camber on the outside ski improved the contact of the carbide with the track to improve cornering bite. The extended offset on the LH ski spindle from the chassis centreline reduced inside ski lift when Gene was leaning into the corner.

Rupp 3rd Dimension 1974

IFS was the Original Chassis Design

When I interviewed Tedd Pierce for this story he told me he had originally planned on an IFS front ski suspension for the 3rd Dimension (3D) race sled and was ready to build it. Unfortunately the new Rupp management team was funding the SnoPro project with the purpose of developing new sled designs and features for the following year production sleds (1975). The estimated cost for an IFS equipped sled would top $2000 putting it out of reach for most consumers to afford. Rupp management were struggling to get the company back on its feet and building more expensive and complex sleds was not a priority, so Tedd had to shelve his idea.

When the team arrived at Ironwood, they could not believe their eyes when they saw the Villeneuve Alouette twin tracker. Here was IFS on a sled, which is what Tedd had wanted to do with the 3D Rupp racer. The Alouette was built to win races with outside the box thinking. Tedd had wanted to do the same but had his ideas shut down. The reader is left to imagine what would have happened on the racetrack that year and if the long-term future of Rupp would have been more secure had it had allowed Tedd to build his IFS racer.

Kohler Power replaces Tohatsu for 74,

The ‘73 Magnum 440 used a Tohatsu motor with Tillotson HD carbs. Gene Bloom had that motor figured out and it ran so good that he competed in the 650 class with it. In 1974 the company had switched to Kohler of Canada two strokes on its production sleds and consequently Kohler RS free air motors with Mikuni carbs would power the new 3D racer. The race engines arrived in early September and from there they had to figure out how to mount them, build pipes, learn how Mikuni VM carbs worked as well as establishing base line jetting. If that was not enough, clutching calibration was also on the list.

Tedd and Gene faced a daunting task, and with the help of Jim Grieg from R & D, began working day and night, literally. When the sleds hit the racetrack, fans all dream about being a factory race driver. The reality, according to Tedd Pierce, was they were literally walking zombies leading up to Ironwood.

Rupp 3rd Dimension 1974
Photo Credit: Ed Chestney

Tedd recalled, “We got to the point that we worked for 36 hours and slept for 6 hours and then worked for 36 and slept for 6 hours. This cycle continued for weeks till we were in a good place.”

An example of the preparation was designing the expansion chambers for the engines. “Kohler sent us the basic dimensions for the pipes for each motor. We took their data plus applied our experience with building pipes and we came up with the dimensions needed.”

Today most tuned exhaust pipes are hydro formed or stamped. Tedd Pierce was not so lucky. His pipes were works of art made by making the sections out of octagon sections and then cutting them to fit into the chassis.

“We quickly discovered using aluminum was not a great idea as the heat dissipation prevented the pipes from maintaining temperature. This threw out all of our pipe calculations, which are based on optimal exhaust temperatures, which is crucial to return unburnt fuel back into the exhaust port before it closes. The engines were soon found out to be down on power. On the flip side when we fired the sleds up at Ironwood for the first time and took hot laps around the track the pipes made a very distinctive sound. That sound generated a lot of attention to us as everyone thought we had something top secret under the hood. Once the first race was held that myth was blown out of the water as the sled had trouble getting out of its own way!”

“Kohler and Mikuni technicians worked with us all season and eventually Lyle Forsgren, who had left Rupp to move to Mercury, supplied us with some Sno Twister pipes which improved performance.”

Old Meets New – Rupp Rails

Racing into the first corner the slide suspension utilized a set of leaf springs in the front end, which controlled weight transfer onto the skis. The “Rupp Rails” slide suspension first appeared on the ‘72 Nitro. Lyle Forsgren used a series of wedges to adjust the spring tension on the front of the track. The rear of the suspension used torsion springs and a single shock mounted off center to the left hand side of the sled. The rails were machined with a series of holes to reduce unsprung weight with magnesium brackets to locate the rear idler wheels. This all contributed to a super light track suspension. The team used rubber tracks or Kalamazoo 15” x 120” titanium cleated track.

Tunnel Mounted Engine

The 3D still had the motor sitting in the center of chassis on top of the tunnel. Rupp was the last OEM to use this chassis configuration. The engine location in the center of the chassis made it easier for Gene Bloom to throw the sled sideways into the corners. The 40” ski stance combined with the fuel tank now tucked on the left hand side over the left ski off set the weight distribution over the inside ski. This was without a doubt the most exotic tunnel mounted engine chassis ever built. Looking back with the limited time the race team had to build three race sleds and the late delivery of the new Kohler Race engines the team could not have built a new forward mounted engine chassis in time for the race season start. The team went with a design they knew and improved it by using exotic materials to construct it.

Looking Back 45 years ago

45 years have passed since the Rupp 3D with Gene Bloom piloting the sled and Tedd Pierce doing the wrenching carried the Rupp name into battle. Carrying the Rupp name and reputation on their backs against the might of the mega factory teams of Polaris, Arctic Cat and Yamaha was a daunting task. The Rupp 3D may not have lit the snowmobile world on fire as they had dreamed it would, but it did succeed on other levels. First they kept the Rupp brand name alive for thousands of Rupp Riders. Second they continued to believe in themselves and the machine they had created.

Gene Bloom had his best showing in Bangor Maine in the 340 classes claiming 4th place. The team continued to compete all winter until the money ran out. All of the teams in SnoPro continued to support Rupp by holding fundraisers at each race to keep the SnoPro show going. The Rupp 3D chassis had its heritage in the early 60’s with the tunnel mounted engine and 1974 would be its last hurrah. Gene Bloom rode the sled throttle to the bar down the straights and throwing it sideways around corners on the verge of wrecking. It sure is more fun that just sitting and turning the skis. Heck, snowmobiling was about fun and Rupp’s slogan said it all – Live it Up Rupp!

By Hal Armstrong – SnowTech Canada

Photo credits: Jim Beilke (SnowTech Magazine)

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Snowmobile Racing's Early Years

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