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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 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.


  1. Nice to see more information, but could you please asked what is different with the Next Gen Ctech 2 fuel system they have on the web ? What is different ? Injectors . Map points? It has been out on the site for over a month and have not heard anything more about it.

  2. What every single person wants to know, especially ppl laying down 20k on a sled to get this new motor is actual hp numbers? And how does it actually compare,real world results to the old 800 and more importantly the 850 competition. I have a 800 cat that is not even close to as fast as the guys I ride with 850s so I’d rather not go and lay down 20k on a sled I’ve never ridden and then find out that the doos and Polaris are still more powerful. Cat has no problem proudly calling the thundercat the fastest production sled, so my feeling is that if the 858 was the new most powerful and fastest sled in the 850 class we would be hearing that. And I haven’t heard anything even close to that on any ride reports as of yet! And no we dont ride dynos I know that, but as a die hard cat guy i know that in history speed and power alot of times is what we hang our hats on when polaris and doo guys are making fun of our cats. In the group’s I ride in I’m the ONLY one on a cat and get harrassed all the time so I personally love it when I leave everyone in the dust of my 22 thundercat. And I also hate it when they leave me in there dust when I’m on my 19 800 cross country.

    • How often do you ride wide open? I know of no place where you can do that all day, unless you just race on the lake. The problem is this winter has been a total disaster for most sledders. I did watch a podcast with the boys on snowest and they were talking to Dave McClure. He said they ran the Trail version of the 858 at 6000 feet and were getting 120 out of them.

      • Just because you can’t ride hard, or race your buddies, doesn’t mean others don’t. Lots of actual snowmobiliers do.
        No one buying an 858 will be happy if it’s not at least as fast as the compitition. Textron has had 7 or 8 years to build a sled faster than the 850s.
        The 858 really should be faster than the 9r, since it’s been out for a couple of years now.
        There has been one 2025 858 ran at dynotech, with 6 hours on it, it made 167 hp

        • And was not the production engine specs, because they will keep working on it till production. You are such an angry man. Relax! Was not talking to you.

    • well theres your first problem, i also have a 19 cross country and your not beating anything on that other then they’re asses out of the hole for 100-200 feet.

  3. Snowest did a seat of the pants review, you can see how that went. I agree with all the guys dropping 20k and wanting some real hp and speed numbers. Years of development should result in a holy crud that thing rips, weather it’s hp or clutching and I haven’t heard that anywhere

  4. I wish they could loose 5Lbs on that 20+Lbs of a suitcase, exhaust can ! They been using the same old can since 012 & maybe longer then that. It’s an amazing difference when I put my 3lbs Titanium can on my sleds. Even on my 600 Catalyst it made a big difference. Richard, do you have a Clutch kit in your 8000 ? That plus an aftermarket tune pipe. Really wake up the Ctec 8000. Good Luck on your 858 decision.

  5. Krom is right…And now the 9r is available on trail sleds. We all know ski doo with the billions of dollars they have will have there next best engine soon also. So cats best shot isnt even on par with the soon to be out going competitions 850s. I knew when ordering, before I was able to ride that my 04firecat 600 was 118 hp. 2010 800ho was 165, 09 suzuki turbo was 177. 2017 thundercat was over 180. When cat knows there leading a segment they have no issue with letting it be known. When they under perform in a segment they say things like 11% more power and torque. 858 sounds badass but my feeling at this point is cat misses the mark AGAIN. I’m still hoping they can shoe horn a 4 stroke turbo into catalyst. Or maybe they have the 2 stroke turbo ready soon that they have patented.

    • Watch the video on the re evaluation. As much if not more than the 9R. Difference is, you probably will get to ride the cat. Polaris? When do they get the P22 to not destroy the left side of the sled?

  6. I sure hope when the production motor comes out this fall, its everything they have been claiming. Cat is so far behind they can’t mess this one up.

    On another note, if anyone is at the factory, please knock on the door for the dirt division and see if anyone’s home? Gone fishing maybe?

    • When I did the demo ride March 2nd. The engineer said they have the High elevation stuff done . But Low Elevation wasn’t done do to no snow. Said he spent the week before testing on a lake in MN. Because they got a couple inches of snow . So they might not be 100% done when the 858 are at the dealership next Fall. Probably a ECU update next winter. You can only blame Mother Nature for that Side note , I’m still waiting for my SSI clutch for my 600 do to this crappy winter.

    • It’s pretty apparent the E-Z-Go morons have abandoned the dirt division. They were all full of bluster and bravado, blowing sunshine up our (dealers that is) *&^. They were going to take Polarass to the woodshed, blah, blah, blah. Then came the name change debacle. Stampede went thud, Havoc went double-THUD, and it went down in a blaze of glory. Bunch of shysters.

  7. I find it hard to believe cat gave snowest 3 completely uncalibrated terrible machines to ride and review. And then said sorry try these machines instead.

  8. I bought a 2010 snopro 500 new, and same thing picked it up and dealer told me they were waiting on a ecu reflash cailuse final calibration wasnt ready. Never came that season. So had a full riding season of terrible run quality and starting issues. Gotta love cat

    • What’s sucks on the 500 SnoPro. The race dept. probably had a cross country tune mid season. Your dealer maybe could have shipped your ECU to them. Hopefully they can do some 858 ditch testing this week. Parts of MN mite see 2’ of ❄️‼️

    • Arctic Cat EFI specialist Terry Anderson was a busy guy at the I-500, reflashing the ECUs on all the Sno Pro 500s. Terry reflashed my sled’s ECU, and the result is great: no more overly-rich bottom end during the initial take-off and slightly crisper mid-range. There will be a reflash for all Sno Pro 500 owners coming soon.

      As a side note, the 500 EFI engine is calibrated to run on 87 octane fuel. Don’t use higher-octane fuel than 87.

      that’s from January 2010…

        • “As a side note, the 500 EFI engine is calibrated to run on 87 octane fuel. Don’t use higher-octane fuel than 87.” … it’s also in the ARCTIC CAT race manual for the sled.

          There’s nothing wrong with 87 octane as long as you keep burning it. It’s long term storage of 87 that degrades fuel lines and components. Towards the end of the season (because we can get it) I start running 87 non-ethanol fuel and do my best to make sure the fuel system is full of it rather than ethanol blended 87.

          You just have to be smart and strategic, which is obviously challenging for some.

      • Buy the Speedwerx clutch kit and timing key. It requires 91, it wakes the little 500 right up. I had it in my daughter’s RR4000. Buddy ran it in his daughter’s 500 SnoPro.

  9. How dare they criticize my new sled i haven’t even rode yet!!!
    lol Its good they told the truth and even there cat diehard said there was an issue. Look how quick they where to fix the issue and redeem themselves. You know it will be as fast or faster than any 850. Have they ever not been? of course not. Surprised no one noticed them saying how great the plastic running boards where last year but this year they hated them? I’ve found it depends on temp and boot soul myself but odd there heavier than aluminum boards. I think when it goes turbo is when its really going to shine. more stroke, more time for boost to build.

  10. I noticed a significant difference in harmonics, and understand that was part of the design criteria. The other thing I noticed was a much more linear power output. In my opinion, as long as you’re flogging the 800 it’s fine, but if you try to modulate power it doesn’t like that. The 858 was perfectly happy at any speed – kind of like the Thundercat, which to me is one of the smoothest snowmobile powerplants ever created. I think they did a great job with the 858!

  11. Ok I’m over the hill and totally out of date y’all. But the bosses on the bottom of the case that look like cylinder carb mounts are fascinating my OCD. What bolts there?


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