Evolution Of An Arctic Cat – THE TWIN SPAR

Penned back in 2006 by John Sandberg “Evolution of an Arctic Cat” dives into the behind-the-scenes story of how Arctic Cat engineers developed the Twin Spar F Series, and Jaguar. It was a time of big changes in Thief River Falls, moving on from the Firecat and pushing hard for more comfort, adjustability, and cleaner-running sleds. Sandberg’s story gives a cool look at how the team brought ideas like the Twin Spar chassis, Infinite Rider Positioning, and the Z1 4-stroke engine to life, all key pieces that helped shape the next generation of Arctic Cat snowmobiles.

The first production 2003 Firecats hadn’t even shipped to dealerships when Arctic Cat engineers turned their attention to what would eventually become the new Jaguar and F Series. It was the fall of 2002, and the winds of change were starting to blow in Thief River Falls.

            “We’d just released the first Firecats,” says Roger Skime, Vice President of Engineering. “We knew they were going to be lightweight, high-horsepower machines that would be tough to beat across the lake. But we also knew we needed something different five years down the road.”

            That “something different” would be shaped by customers who wanted more comforts and adjustability with their sleds, the engineers’ natural creativity and emissions requirements from the Environmental Protection Agency (EPA).

A product planning committee, made up of representatives from Engineering, Marketing, Sales, Manufacturing and Parts/Accessories, gave the green light to a  project sled called “F3” that would incorporate every division of engineering to develop what they believed would be the most comfortable snowmobile to date.

Chassis: Rigid Requirements

From the outset, Arctic Cat leadership established important goals for the new chassis. It had to place the rider forward, but with simplified adjustability to the traditional position. To deliver the best possible handling, the chassis would be more rigid than anything produced to date. And it had to accommodate two entirely different laydown engines.

            The first step was to determine the ergonomic platform using a Firecat chassis that was chopped and reconfigured to allow variations in handlebar, steering post, seat and foot positions.

            “We wanted the rider’s feet further forward, because it’s important to keep a 90-degree knee bend to maximize comfort and to reduce fatigue,” says Kevin Thompson, the project engineer and the person who managed much of the project. “We wanted a chassis that any rider could pilot for 200 miles without getting fatigued.”

            By the spring of 2003 and after several iterations, the crew had confirmed the desired foot, butt and hand positions—contact points that would remain consistent in all chassis development. They’d also “tipped down” the front bulkhead, which helped achieve flat, ZR-like cornering characteristics and increased ground clearance at the front of the rear suspension.

            While the first generation chassis was being finalized, Senior Industrial Designer Nathan Blomker was producing dozens of “blue sky” styling sketches of F3. Beginning with drawing number 1, he included three elements that would eventually achieve production status: adjustable handlebars, seat and windshield.    

            “In the past Styling didn’t get involved until the chassis, engine and airbox locations and shapes were known,” says Blomker. “With F3, styling was integral in the design of these individual components, particularly the chassis’ twin spars.”

            Several factors pushed the team toward the Twin Spar design. One was rigidity. With ever-increasing demands that riders were placing on chassis performance, coupled with increased power-output and suspension capability, all future chassis designs needed to be stiffer. Twin spars also allowed lower placement of an engine and, from a style perspective, complemented the visual lines Blomker was trying to achieve.

            Charged with developing a twin spar chassis that incorporated the ergonomic package and certain styling components were two Computer Aided Design (CAD) engineering aces, Ken Fredrickson and Paul Malmanger. Their first attempt had exposed spars that were visible outside of the hood components.

Once the Arctic Cat product planning team agreed on styling drawings, people like Nathan Blomker went to work on foam models for further styling evaluation. Here Blomker does more shaping to the life-sized model.

“We had a working prototype of the first twin spar chassis on the snow during the winter of 2003-04,” says Fredrickson. “It was interesting, with unique air intake and exposed spars, but it was heavy and expensive to produce.”

            They responded by moving the spars inside the hood.

            “Once we moved them inside, we immediately hit the rigidity requirements we’d initially established,” says Malmanger.

            A fabricated version of this second generation twin spar chassis proved exceedingly rigid when evaluated using computer-aided Finite Element Analysis (FEA) testing and during stress tests in the NVH Lab. These tests were confirmed when the chassis was placed on a unique, hydraulically actuated “twist rig” that cycled thousands of exaggerated motions for days on end. Small hot spots—locations where the stresses might manifest in the form of stress fractures —were reengineered and fixed.

            A critical requirement set forth in the original product plan was that it be easily and quickly adjustable to a wide range of rider sizes and riding styles, including easy trail cruising and stand-up-pounding through bumps.

It would take 12 attempts via CAD design before design engineer Jesse Olson and others settled on what would eventually be called the Infinite Rider Positioning System (IRP).Using the support rail that angled back from the top of the steering support to the middle of the tunnel.

The crew developed the necessary structure that allowed the seat to move forward more than three inches, while moving it vertical more than two inches without using any tools.

Complementing the change in seat position was an equally creative adjustable handlebar. Using a cam-lever mounted on the handlebar riser block that essentially loosened the handlebars and riser, Olson designed an 11-position system that offered 3.3/2.1 inches forward/vertical movement. Just as important, it also allowed 85 degrees of handlebar rotation, which meant no compromise of awkward handlebar angles or brake or throttle lever positions when the handlebars were adjusted forward or back.

Other new features to help Arctic Cat consumers ride better, faster and longer highlighted important advances in technology. For the first time in company history the modular chassis would be assembled using self-piercing rivets and alignment locations, which are far stronger and more durable than regular rivets and less likely to warp like welded components. A rack steering system and front suspension geometry were optimized for greater steering movement than the Firecat, which produced a tighter turning radius. And a unique, two-sided rear heat exchanger actually captured and held snow to deliver cooling.

Dedicated 4-Stroke Engine

Knowing that snowmobilers were divided in their opinion of 2-stroke versus 4-stroke engine design, the product planning committee was very clear with another directive: riders would have the choice. That requirement would set into motion a series of challenges that would test the creativity and imagination of both chassis engineers and the engine department.

            Development had already commenced on what would become the Z1 4-stroke engine even before project F3 began.

            “We knew we would face strict emissions requirements back in 2001, but we didn’t know what they were at the time,” says Chris Wright, Manager of Exhaust Emissions Compliance. “We initiated the Z1 project under the assumption that it would have to be very, very clean.”

            Headed by Engine Group leader Brad Maus, a crew of engineers determined that the new 4-stroke engine had to be a narrow parallel twin-cylinder with EFI. It had to produce 120 horsepower at 8,500 rpm. Very little, if any, engine braking would be tolerated. And most importantly, it had to be an engine specifically built for a snowmobile.

            “We didn’t want a GSX-R 1000 4-cylinder engine converted for a snowmobile application,” says Maus. “Besides the substantial cost of buying and then converting a motor like that, a parallel twin can be placed in the chassis with a lower center of gravity, and they are narrow.”

            Suzuki Motor Corp. assembled their 4-stroke engine specialists and produced a two-dimensional CAD model of a stand-up, parallel twin. Arctic Cat used the drawings to construct a foam model of the engine to test for fitment inside a chassis. Not long after the first models were constructed, Arctic Cat gave another parameter for the evolving engine: it had to be a laydown design.

            Suzuki went back to work and, several months later, delivered two first generation working prototypes, one that had a 180-degree firing order and the other with 360-degree firing. Both engines were mounted in then-prototype M Series chassis for engineers to evaluate throttle response, acceleration, vibration and general feel. The consensus of the group was that the 360-degree firing order was superior, offering incredibly smooth power.

            Race legend and Drive Calibration Engineer Larry Coltom and others soon had a clutching package that captured the strong power characteristics. The power pulses of the Z1 engine were so strong that the crew began developing a more robust four-post drive clutch.

As development progressed on the power characteristics, engineers made important gains to minimize engine braking with a device they were calling Idle Speed Control (ISC). Utilizing the computing power of the engine’s ECU, engineers linked information on engine RPM and throttle position to open the butterfly valves in the dual throttle bodies during deceleration, all but eliminating unwanted engine braking.

            With its many acoustic tools and jury listening room, Arctic Cat’s state-of-the-art NVH (Noise, Vibration and Harshness) Lab was used to help shape the engine’s sound quality, as well as helping to design an engine mounting system that would meet an increased durability requirement, with reduced vibration.

2-Stroke, No Smoke

While the 4-stroke team continued development of the Z1 engine, an experienced crew of engine specialists pushed the boundaries of 2-stroke engine development on a big twin —a project that began in the spring of 2002.

“We knew we wanted a big twin that was clean, although the EPA hadn’t yet set a target,” says Greg Spaulding, Engine Group Leader.

Building a high-horsepower twin wasn’t a problem, as the crew had just put the wraps on the 140-hp 700 twin in the F7 Firecat. But building a clean, high-hp engine was something altogether different.

The crew started with certain parameters. The engine would be 1000cc with the goal of at least 160 hp. Batteryless-EFI was a given, as was the low-center-of-gravity “laydown” architecture.

“This was the first motor we’d developed entirely for EFI,” says Spaulding. “For emissions reasons we opted for a long-stroke, low-rpm design.”

The crew leaned heavily on the Exhaust Pipe Temperature Sensor (EPTS) technology they had developed years earlier for the Sno Pro 440 race sled. Linking pipe temperature with ignition timing, fuel quality, exhaust valve position, throttle position, air temperature and density, a highly sophisticated engine management system helped ensure the most efficient combustion at any given moment of use.

Other gains in clean emissions came from twin sparkplugs on the cylinder head, which promoted more efficient combustion (especially at lower rpm) by starting ignition over a larger area. Likewise, development on the APV exhaust valves system produced multiple valve positions (compared to the open/closed position of previous systems), which also improved the engine’s efficiency.

Hundreds of dyno runs in the company’s emissions lab cataloged the effects of combustion chamber development.

“By the time we’d developed the motor for pre-production calibration, we’d made more than 3,000 dyno runs in three years,” says Dan Johnson, Drive Systems Group Leader.

The impressive development yielded better-than-hoped-for results. The new 1000cc engine produced 162 hp, and 117 ft.-lbs. of torque at 7400 rpm and an exceedingly wide powerband that made clutching extra easy. Other features added usability, such as a large diameter recoil and auto-decompression (actuated by the APV valve location so there is no loss of peak hp) for easy hand starting. An internal bypass in the cooling system promoted quick engine warm up, and a D-shaped throttle body cam provided progressive throttle lever effort. Better still, the emissions numbers were better than the crew had hoped for.

Evaluating the Results

Computers accelerated the most intense testing and evaluation effort in company history, but as a company of passionate, dedicated riders the final proof was how the chassis worked in the real world, using what still may be the most important yardstick: seat-of-the-pants riding.

During the winter of 2004-05, several groups comprised of field test riders and engineers logged thousands of miles on 35 prototype sleds. From Michigan to Minnesota, Manitoba to West Yellowstone, crews evaluated, tweaked and calibrated these heavily disguised prototypes, ratcheting up the refinement while setting the stage for the largest single new model unveiling in company history.

“At this point, the entire project was coming together and with results that pleased everyone involved,” says Lynn Berberich, Coordinator Controller, and the guy who was responsible for tracking the project’s schedule. “Both the Z1 and 2-stroke engines were hitting the performance and durability goals. The adjustable seat, handlebar and windshield combination was worth the considerable effort that went into designing them. The electronic ACT Diamond Drive push-button reverse was proving bulletproof. Wind protection was excellent, rider position was exactly as we’d specified and ride quality as good as we’d hoped.”

The marketing plan for the new sleds called for a limited production run of the Z1-powered sled —which was given the official name “Jaguar” —in the winter of 2005-06. Through the summer of 2005 the Styling department created multiple graphic options for Jaguar and a platter of 2-stroke F Series sleds ranging from 500 to 1000cc. There were subtle variations between the Jaguar and F Series sleds, namely the rear seat storage and the windshield, but both versions were otherwise identical.

By November 2005, robotic production equipment like the self-piercing rivet machines were being assembled and located at the main plant in Thief River Falls. Another batch of 40 Z1-powered sleds were hand-assembled using mostly final production components. Many of these sleds would be mocked up with multiple graphics and used during the company’s brochure photo shoot in Wyoming, while the remaining machines saw continued durability testing and ride calibration.

By early 2006 an 800-unit production run of Jaguar Z1s were produced and shipped to Arctic Cat dealers. Though labeled as 2007 models, these machines were ridden by dealers and snowmobilers in the final weeks of the 2006 riding season. During a one-week period in West Yellowstone, dealers and riders logged a total of 80,000 miles on the preproduction Jaguars. The consensus among those who rode it was that Arctic Cat had hit an out-of-the-park homerun. The new machines were more comfortable, had more power and simple adjustability. Handling was better than any previous model in company history, as was fit-and-finish.

Four months later the first full-production F Series sleds began rolling off the assembly line in the form of the F6, followed six weeks later by the Jaguar and F1000, with the F8 slated for production in October. Four years in the making, the newest Arctic Cat snowmobiles fulfilled the promise of every design goal while satisfying the imagination of riders who want the latest in technology and comfort.