INSIDER TECH – UNLOCKING THE POWER & TORQUE OF THE NEW 858
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There’s little question the new 858 is easily the most talked about engine in the industry for model year 2025. Arctic Cat’s new big bore was first confirmed to members of the media way back during Hay Days 2022. Then last year, the engine size, early details, and a first look were revealed when the Cat crew showcased the new 858 along with the G8 Display at Hay Days 2023. Finally, this winter, the complete package became reality, and the 858 mounted low in the Catalyst platform hit the snow pack for early demo opportunities, and we all clamored for a first-ride experience.
By now, most of you have read and watched plenty of first-ride reports from demo ride participants, members of the media, and here on AI. The overall consensus is the new 858 hits all the marks … more torque where we want it … and more horsepower that we crave, putting it squarely in the big-bore hunt. What’s more , the new 858 overall engine package is lighter and compliments the low center of gravity and centralized mass design of the Catalyst platform for what I feel is the most responsive and fun to ride sled on snow.
While in West Yellowstone earlier this month, I had a chance to get some one-on-one time with Cat engineers and gain some further insight into the 858 – here’s what I learned.
LAY IT DOWN – As with any new engineering project, the 858 started with a very specific set of goals the team wanted (or should we say) needed to meet before the new engine could make its way to the snow. They included the obvious, such as meeting defined cost, power, durability, and reliability targets. But there were other more specific targets, some of which are unique to Arctic Cat, that needed to be achieved. One was the need for a laydown engine design. It’s no secret to Arctic Cat faithful, that the laydown engine design has been a hallmark trait for the brand dating back to the formidable Firecat legacy. A laydown design allows for a more compact and centralized mass configuration within the chassis. While it creates other challenges, such as having to design both an air-intake and exhaust system in front of the engine, Arctic Cat believes in the value and benefits of this architecture, thus the 858 had to incorporate the advantageous laydown design.INTEGRATED CASE – The new 858 was also engineered to optimize the engine mounting system by integrating those mounts into the case. This allows the 858 to be mounted as low and as close to the rider as possible in the Catalyst platform resulting in improved handling and responsiveness and in turn a very lightweight and nimble feel. This integrated mounting design also reduces parts which reduces weight and increases durability.794 VS 959 – When comparing the new 858 to the “old” 800 there are two primary areas where we can see a very defined difference. Obviously the new 858 has more displacement, but it’s how it arrives at that new found number that is of interest. Both the old 800 and the new 858 serve up an identical 85mm bore with the new 858 having a longer stroke (75.6mm versus 70mm). There’s a multitude of benefits with this “stroker” route, (one of them relates to the new exhaust valve design we’ll talk about in a bit), but overall this architecture delivers increased efficiency and a “right sized” engine for the Catalyst platform. What’s more, the stroker design produces an engine that is 3 lbs lighter than the “old” 800 while producing 11% more horsepower and 11% more torque. More than just a longer stroke, the new 858 touts a new crankcase, new exhaust valve system, new air intake system, and a new exhaust system.CRANKCASE DETAILS – To accommodate the longer stroke, the 858 crankcase had to be enlarged. Since Cat engineers were already retooling the case, they also looked for ways to improve flow, reduce weight, and further enhance chassis integration with engine mounts becoming part of the case. One such change is how the reed cage has been moved closer to the engine to deliver a quicker, crisper response. In addition, engineers also incorporated durability and reliability improvements into the design such as improved crankcase sealing.OLD 800 VALVE SYSTEMOLD VS NEW EXHAUST VALVES – One of the biggest design changes to the new 858 are the exhaust valves. Gone is the old 3-valve design (TOP IMAGE) which had 30-individual parts per cylinder, and in its place is an all-new single valve system (BOTTOM IMAGE) that uses half has many parts and offers significantly improved performance. For those who may have cleaned or torn-down the older 800 design, you’ll remember the system used a flat-slide main valve and rotary side valves (for the auxiliary ports). The new design uses a single valve operated by a servo motor that opens and closes the valve (the old design relied on a spring to close the valve). The more streamlined design and the manner in which the valve operates eliminates several sliding and high-friction contact points resulting in much smoother actuation. While all this is a much welcomed improvement, it’s the geometry and range the new valve delivers that is the real game changer. The new system allows for 250% greater port height change, with an auxiliary port height increase that’s 33% taller. This means the new 858 can produce greatly increased low end torque and efficiency AND more top-end power.BEST OF BOTH WORLDS – To dumb down the benefits of an exhaust valve, think of it as providing two different engine designs in one. If you want an engine with gobs of low end torque and increased efficiency, you want a lower and smaller exhaust port. Conversely, if you wanted an engine that produced all-out RPM and top-end power, you would want a larger, and higher exhaust port. A variable valve delivers both…and the more you can vary the height and size of the port, the better your engine can deliver the best of both ends of the spectrum. That’s the new 858. The above image shows how much height and size difference there is in the two exhaust valve designs. The red is the valve and also represents the “area” of variable port height. As you can see, the new design allows for dramatically more height change. NEW INTAKE SYSTEM – Arctic Cat engineers used every opportunity they could to further improve the overall package of the 858 Catalyst. An all-new, simplified intake system reduces parts, reduces weight, delivers a tighter seal throughout the air-flow pathway, and reduces sound levels. Mountain riders will also appreciate a secondary under-hood inlet that eliminates the chances of “capping off” when riding in deep powder.NEW EXHAUST SYSTEM – Of course a new engine requires a newly tuned exhaust system. Once again, Cat engineers used the opportunity to further improve the entire design. The new 858 exhaust reduces weight and features more durable mounts.
