Details of the Arctic Cat 858 Engine | Mountain Sledder
October 5th, 2023

Details of the Arctic Cat 858 Engine

Arctic Cat recently revealed the news mountain riders have been waiting on since the first announcement of its next-generation snowmobile platform Catalyst: the details of a big bore engine developed alongside the chassis to compete with the modern 840+ cc engines of its competitors.

The new era for Arctic Cat will be powered by a 858 cubic centimeter displacement two-stroke engine, developed in-house by Arctic Cat engineering.

Arctic Cat 858 Two-Stroke Engine

Arctic Cat says the 858 engine was developed in parallel with the Catalyst platform from the beginning for seamless integration in to the new chassis. However, it just wasn’t quite ready to go when it was time to reveal the new platform. Hence why the 600 cc engine was the only powerplant made available for the first year of the Catalyst platform in model year 2024, and any talk of a bigger engine was hush hush.

However, Arctic Cat has announced that starting in model year 2025 (available in Spring 2024), the 858 engine will be available, which will make the new platform mountain models especially that much more appealing to hardcore backcountry and mountain riders.

Arctic Cat 858 Engine

So what is the new 858 engine?
So far, we’ve seen no official evidence of Arctic Cat referring to the new 858 engine as a C-TEC2 variant, but we can assume that at least some, if not a significant amount, of the architecture will be carried over from the reliable and strong C-TEC2 800, 794 cc two-stroke engine. That makes a comparison in order.

Arctic Cat 858 Engine _-2

858 Engine Horsepower Speculation (and How It Compares to C-TEC2 800)

The OEMs are reluctant to go on the record with horsepower numbers. The reasons for this are well-documented and understandable—every dyno reports a different number and besides that, it mostly amounts to a pissing match anyway.

As such, Arctic Cat historically has simply referred to the legacy C-TEC2 800 in the “160-horsepower class”.

Ask riders though (we’re looking at you, Cat guys), and many will solemnly declare that the C-TEC2 800 pulls as strong as Polaris’ 850 Patriot (actually 840 cc) and BRP’s Rotax 850 E-TEC (849 cc). We’ll neither confirm nor deny any allegations, but if true, that claim would put the C-TEC2 800 into the 165 horsepower range.

Sticking to the plan, Arctic Cat has currently also made no specific number horsepower claim for its new 858 engine. But, the OEM is willing to reveal an 11% increase in output over the C-TEC2 800, despite just an 8% increase in displacement. And when you further consider the new engine reportedly weighs 4% less than the C-TEC2 800 it supersedes, that 11% horsepower increase is starting to sound very appealing indeed.

Arctic Cat 858 Engine

Wild assumptions summarized: if you believe riders who put the C-TEC2 800 on par with the output of the newer and higher displacement naturally-aspirated engines from BRP and Polaris, then some basic assumptions lead us to imagine that potentially the new 858 from Arctic Cat could produce as much as 183 horsepower. That’s a pretty positive outlook. Now slap it in a lighter and more nimble chassis, and you’ve got something to be excited about.

On top of that, let’s not overlook the parallel (and yes, related) 11% torque increase.

How was this achieved? Well, as they say, there is no replacement for displacement. The 858 engine reportedly uses a longer stroke to increase displacement over the C-TEC2 800.

C-TEC2 800 Bore x Stroke (mm): 85 x 70 mm
858 Bore x Stroke (mm): 85 x 75.6 mm

This reduced ratio of bore to stroke dials back the oversquare nature of the engine, which in theory should produce more torque at the lower range of the rev spectrum. More torque equals more horsepower, under the bold assumption that all other things remain equal.

That’s all an oversimplification of course, but from a rider’s perspective, the suggestion of a little more grunt down on the low end is enticing.

858 Power Characteristic

Carrying on that train of thought, we’d argue that the responsiveness and power characteristic of an engine in a mountain sled are much more important considerations than simply small differences in peak horsepower.

As an example: have you ever ridden a similarly spec’d RMK 9R next to a Patriot Boost in tight trees? We have. There’s a pretty huge difference in riding experience there, and it has much more to do with responsiveness than the difference in horsepower.

But many engine characteristic like responsiveness are harder to quantify, and have more to do with feel.

Until we ride it, we won’t be able to answer questions such as: How quickly does the engine accelerate at various engine speeds and throttle positions? How smooth is it? How does it respond when you’re chopping on and off the throttle? What happens when you pin it from a standstill? How well does the clutching work to get that power to snow in a linear fashion?

858 Exhaust Valve System

In the meantime, Arctic Cat has revealed some interesting details about the new engine design for us to chew on, including a description of a new exhaust valve design.

Arctic Cat says the new patented exhaust valve system is the latest, most advanced in the industry. It uses an ECM controlled push pull actuator that provides what the company describes as complete control over the opening and closing of the exhaust valve. The valve maintains a tight clearance with the piston at all positions.

Arctic Cat explains that the geometry of the new exhaust valve system allows for 250% greater port height change for increased low end torque and efficiency.

As part of this, the auxiliary port height can grow 33% taller.

Sounds cool, right? The practical result they say is a linear torque curve and cleaner emissions.

Laydown Engine and Intake System

Arctic Cat’s laydown engine design means the intake and exhaust systems are on the same side of the 858 engine. This provides the advantage of a lower and more centralized mass by moving the low density (air filled) intake system in front of and on top of the engine, rather than behind. It’s one of the key design principles behind the mass centralization theme of the Catalyst platform that’s been discussed at length.

The intake system has been designed to maximize airflow, including carefully placed exterior intake ports that make use of Frogzskin pre-intake filters.
For the really deep days when those exterior intakes can potentially become buried in snow, Arctic Cat has designed in multiple secondary under-hood intakes ports to prevent any possible constrictions of the air supply to the engine.
Remember the days when you had to reach over the hood to clear snow from the vents to stop your sled from bogging in over-the-hood pow? Hopefully that experience will exist now only in our memories.

Arctic Cat 858 Engine _-3

858 Engine

Here are some other 858 engine details revealed by Arctic Cat.


  • Enlarged to accommodate the longer stroke
  • Reed cage moved 12 mm closer to the engine
  • Increased ACG venting
  • Improved sealing features added
  • Engine mounts are integrated into the crankcase
  • New design for improved flow, weight reduction and integration with the chassis


Exhaust System

  • 858 exhaust system tuned specifically for new engine and platform
  • Reduced weight
  • Durable mounting

Intake System

  • The intake system has been simplified
  • Reduce number of parts and fewer joints (less to seal)
  • Reduced weight
  • Sound level reduction
  • Under hood inlets as secondary supply

Arctic Cat 858 Engine Summary

So it seems there is quite a lot of interesting and innovative design that has gone into the development of the new 858 engine from Arctic Cat.

Naturally, out of all the information revealed by Arctic Cat, the pieces that will stick are the number of cc and the promise of 11% more horsepower. We’re simple creatures, aren’t we?
Ultimately riders will judge the 858 engine by its performance on snow, not by the bullet points of a PowerPoint presentation. But we won’t experience that for some time. A lucky few will ride the engine and sled this winter, and fingers crossed some Mountain Sledder staff are amongst those.

However, it’s pretty safe to assume in the meantime that this engine hold plenty of promise once it’s housed in the Catalyst platform and running WOT through three feet of fresh.

We can’t wait.


– MS