Yamaha may have entered the four-stroke sweepstakes last, but the Japanese-based company has done it best with the all-new RX-1 high performance snowmobile. First and foremost, the RX-1 is a true snowmobile. It rides like a high performance sled. It handles like a high performance sled. The clutches deliver power like a snowmobile drive train. But it screams like a high revving, high powered super sport motorcycle.
A direct step from the R1 motorcycle, the Genesis Extreme snowmobile motor has a patented five-valve head design to maximize airflow across a very broad rev range. There are three intake valves to suck in fuel with dual exhaust ports to scavenge spent gases into a specially tuned exhaust system.
The four cylinder, 998cc four-stroke is mounted transversely in the chassis with the four 37mm constant velocity carbs facing forward and the exhaust routed out the back, under the seat and dumped into a big silencer can. Originally the exhaust was a freer flowing design, but Yamaha engineers decided that adding an "X" crossover pipe at midpoint in the system boosted low-end torque without sacrificing top-end performance. Simply stated, four straight head pipes flow into twin pipes with crossover and continue to the silencer and finally blast out of twin rear outlet pipes.
The base points for the new Genesis Extreme snowmobile engine include:
• Liquid cooling
• 30-degree rearward angle in the transverse mounting
• 998cc displacement from a bore/stroke of 74x58mm per cylinder
• Compression ratio of 11.8 to 1 on regular pump gas
• Forged aluminum pistons
• Remote-mounted dry sump with finned aluminum oil cooler and spin-on oil filter
• Standard four-stroke oil-based lubricants are used
• Rack-mounted Mikuni BSR 37mm, liquid-heated, side-draft CV carbs
• Digital CD with 3-D timing curve
• 425-watt magneto output
• Clutch engagement speed of 3500-3800 revs
• Peak engine speed of 10,200 rpm
• Standard key start
• RX-1 short track pricing from $8,849.
• RX-1 Mountain pricing from $9,149.
Specifically the new four-stroke is designed to rev high, maximize horsepower and out-perform its two-stroke SRX predecessor, which we have dynoed at 140-plus horsepower. The Yamaha motor's design parameters called for it to have more power than the competitions' 800cc big twins. To get the four-cylinder motor's power to the snow is the job of a revamped RX-1 clutch system. The new clutch weights give testimony to the torque available for this power plant.
The weights are big and bulky, not unlike the heads of a small ball peen hammer (kidding!). These are not subtle weights, which suggests that a total mechanical moron could probably clutch this baby and not screw things up too badly. The shift cam has a multi-angle ramp that ranges from 43 to 51 degrees.
Yamaha claims that its Genesis Extreme develops 65 percent more low end torque than the competition and can achieve up to 30 percent better fuel economy.
In fact, Yamaha is so confident of the RX-1's fuel efficiency that it cut the fuel tank size down to 10 US gallons versus the SRX 12 gallon size. According to Yamaha, the new four-stroker will have the same range as the two-stroke SRX. Plus, the change helps put the RX-1 within two percentage points of the SRX fully fueled weight.
The target weight for the RX-1 (equipped with electric start) was to be within five percent of the existing SRX. Yamaha claims that has been done!
To get there, the RX-1 uses construction techniques somewhat new to snowmobiling. The all-new Delta-box chassis features a combination of die-casting, extrusions and stampings that result in an exceptionally stiff, lightweight and durable base. The tunnel and footrests are rather conventional using stamped aluminum. Extruded aluminum carries chassis loads from the engine cradle mount through to the steering platform. The thin-wall die-casting highlights the front suspension area and the front and rear tunnel areas. The engine cradle is designed to allow the four-cylinder motor to be a stressed component of the chassis, adding to overall strength and weight reduction. Unlike conventional engine mounting, the RX-1 engine mounts in a motorcycle-like cradle that serves to reduce engine twisting, while enhancing clutch alignment and chassis stiffness.
The die cast front suspension component locates an entirely new unequal length double wishbone suspension that provides up to nine inches of travel. Large 40mm fade-resistant shocks control rebound with the unequal length arms designed to reduce bump steer and minimize scrub.
"One of the many impressive characteristics of the new RX-1," states AmSnow editor, Jerry Bassett, "was the new front end. Arctic Cat has used A-arms forever to create outstanding handling. Now Yamaha has zeroed in on a precision handling design that let me nail the turns with minimal 'push' during our introductory test ride. I really liked the Viper for handling, but the RX-1 sticks to the turns even better."
To enable engineers to drop the four-cylinder engine as low as possible in the chassis, the new steering system was routed around it. A similar approach has been used in Yamaha's snocross racer. Bearings at key pivot points and double steering pivots are used on the wishbone setup.
On our ride of prototype RX-1s at Yamaha's new Wisconsin test facility, it was discovered that the steering system suffered from an incorrect bushing tolerance which resulting in heavy steering effort and a slowness in response that we have been assured will not be the result in production models.
A new deeper keel ski is used on the RX-1. It's a lightweight plastic design with an aggressive dual-angle keel design that is said to maximize effectiveness in the widest variety of snow conditions. The narrow design is claimed to minimize drag to maximize top speed. The reduced ski wall thickness saves weight.
At the rear is a ProAction SXV long travel suspension setup with high-pressure gas shocks, exclusive needle bearings and multi-spring rates. As with the front suspension, the center shock is also a fade-resistant 40mm design. You'll find Yamaha continues its adjustable control rods and quick-adjust full rate adjuster.
There is a lighter weight chaincase and brake with more ventilation to handle the necessity of hauling in this performance machine. The new handle-mounted grip and thumb warmers raise/lower temperature in finite degrees by simply thumbing a toggle button and watching the LCD display on the digital speedometer screen. Yes, the digital speedo returns. We can attest to the fact that it reads out in triple digits.
I had the sled up to 124 miles hour on a closed one-mile course. My AmSnow compatriot made a run of 126 mph. We have heard reports of 130-plus from the prototypes and we believe them. With the shoreline fast approaching we AmSnow test riders opted for easing back the throttle.
Interesting enough, this four-stroke Genesis Extreme provides an interesting twist on high performance riding - engine braking! With a Viper or SRX, you could let off the throttle and continue rolling at a good rate of speed as the engine would go to idle and the clutches would effectively freewheel. Not so with the RX-1. Let off the throttle at your normal "let off" points and the drive train provides braking just like a gearshift car or motorcycle. This will take some getting used to.
What is this sled like to ride?
Impressively different. Like we said at the beginning, this sled feels, acts, rides and handles like a snowmobile. First and foremost Yamaha has created a snowmobile.
Secondarily this sled has an incredibly smooth, yet impressively powerful engine that just happens to be a four-stroke. The sled drives like a two-stroke on steroids. This 998cc power plant has attitude from the moment you twist the key and fire it up all the way up to top speed - wherever that may be! In a quarter mile we were consistently in triple digits very, very quickly. Cruising at 80-plus mph we could push the butterfly carbs to wide open and feel the sled charge ahead. At 100 mph the prototype test sleds had plenty of performance left. Heck at 124 mph the digits were just starting to come up slowly. There is a herd of power under the narrow razor nosed hood.
While ride time and miles were limited, the ProAction suspension system seemed to be as promised. We have liked the Viper setup and the new RX-1 rear unit seems to be able to soak up moguls well. We'll see when more snows come our way. As mentioned before, the front end sticks extremely well.
Nothing really. But I wouldn't mind a titch thinner diameter bar with a little extra length and more to hold on to like Cat's ZR SnoPro bar extension. I couldn't tell about the steering because it wasn't set properly on either proto ridden. I did detect a bit of body roll, but again, this might not have been so much in evidence if the steering were set up right and I could have countersteered more quickly. So, we'll reserve judgment on that.
Ergonomically the sled is great. The thumb and grip warmers are great, as good as any others. The windscreen worked great. It looks too small, but it really keeps the wind off your hands like Cat and Polaris without being bulky.
And, finally, …that motor. Oh, my. It is a dream. S-m-o-o-t-h! Powerful and screams like a mildly detuned race bike. Hmm, maybe that's what it is!
All I know is that it was quite obvious that Yamaha has given this four-stroke thing some serious thought. If emissions standards tighten up after 2006, look for electronic fuel injection. Heck, the second generation R1 motorcycle has it now. Yep, Yamaha has taken this four-stroke thing seriously. And, fortunately for us, they created a wonderful new snowmobile in the process!