For 2019 Polaris is introducing the all-new 850 Patriot, the most powerful snowmobile engine ever built by Polaris. It was available exclusively on select SnowCheck models and built with pride in the USA. The 850 Patriot builds on the legendary 25-year heritage of Polaris Liberty engines and creates an all-new benchmark for durability, acceleration, and response.
An All-New Benchmark for Durability, Acceleration and Response
Right through the 2018 model year, the Polaris 600 & 800 twin engines could trace their linage back to the 1997 Liberty 700 introduced in the RMK and SKS models, quickly followed by the red, white and blue Indy XC 700. This new 850 is a departure from that architecture and is truly is an all-new motor, all the way from the crank to the ECU. This means that nearly every single part on the 850cc motor is new, except for maybe three of them – the spark plugs and a couple of the sensors. This is significant because it allowed Polaris to pursue design goals centered around performance and durability based on the latest technology rather than goals that required the use of existing (& less expensive) hardware and older technology.
“First and foremost, we have to build the most durable engine in the class,” states Polaris Snowmobiles Product Manager Marty Sampson. “Consumers were looking for the next big iteration in snowmobile engines,” adds Senior Development Engineer Dallas Blake. And while very few components are shared with the previous Liberty engines, the design element of quick throttle response carried into the new project, achieved through light weight, low inertia and a high power-to-weight ratio.
Back in 2013 Polaris was already working towards the development of a new 2-stroke snowmobile engine. The engineering team had complete freedom with the design of this new engine, a “clean sheet” approach. Design targets were to exceed their current (and just upgraded) Liberty 800 and included greater durability, stronger acceleration, improved responsiveness and maintain the agility that Polaris sleds were renowned for.
Polaris told us they prototyped several different bore and stroke combinations, to the point of hitting the snow with each version to test responsiveness and power delivery. In the end they believed using an 85mm bore with a longer stroke was the best combination and gave them the best balance of throttle response, torque and horsepower and a power delivery that was smooth and manageable. The operating RPM is also 8250, the same as the 800, helping to keep clutching efficiency high while making great power and torque.
Why 850cc? Is this in response to the Rotax 850 E-TEC? The development of a new engine like this takes several years and Polaris has been working on this project for more than four years, long before the introduction of the Rotax 850 E -TEC.
The gain in displacement comes from the new low-inertia crankshaft having a longer 74mm stroke, along with a larger clutch taper and high capacity bearings. The crank bearings are all bigger, with a double-row cylindrical “roller” PTO end bearing (instead of using a spherical bearing design). Non-integral crank pins are drilled out to help reduce the inertia.
The bore is the same as the Liberty 800, but these are all-new lightweight 85mm pistons featuring a single steel-ring with PVD coating (instead of a heavier iron ring). The piston features a 3mm thicker dome and is 8mm taller on the compression height to help keep the heat away from the wrist pin bearing. The piston claims 23% more contact area with the cylinder to provide better control of the piston in the cylinder – with less rocking in the bore, also allowing for improved heat transfer as well as stability within the cylinder. We also find larger pins and bearings on both the rod and crank ends, better suited to handle the extra power.
A new 6-bolt monoblock cylinder is mated to new cases and head. The cylinder has a new airflow pattern on both the intake and exhaust side with a new patent-pending exhaust port design. A new 3-stage exhaust valve system (similar to what the 800 uses) features integrated cooling with no external lines. The cooling system has also been redesigned using Computational Fluid Dynamics which means the flow is optimized to move slow enough to absorb the heat and transfer it to the heat exchangers, but fast enough to keep up with demanding conditions. Vents are now found on the mag cover for additional evacuation of hot air.
Polaris went with a one-piece head design with no cover. This delivers the best structural rigidity, featuring a new patent-pending combustion chamber to work with the new engine properties. Another cool feature is the new (patent-pending) thermostat design has been integrated into the coolant overflow bottle to reduce vibration and maximizes thermostat life. The system utilizes a coolant bypass for quicker warm-ups and is set to open at 100 degrees, keeping the big twin cool and making maximum power.
A new engine mounting system is used to attach the package into the AXYS chassis, which means you won’t be dropping an 850 into an existing 800 chassis. New VForce reeds have been designed specifically for the 850 and are matched to new 50mm throttle bodies, featuring a new petal formulation and inner cage seals for improved durability. A reliability improvement is found in a new contact-less Throttle Position Sensor (TPS) for reliable, consistent performance. The throttle bodies are permanently set which means no more recalibrations to keep your TPS settings accurate. There are even needle bearings on the throttle body shaft for added durability of the throttle assembly.
Engine management is controlled by a brand new, faster and far more powerful ECU, the brain box or computer that controls all electronic functions and operation. This more powerful ECU takes all of the information from the input sensors and decides how to vary the output controls for efficient and powerful yet durable operation. There are all the standard input sensors, but it is now fitted with additional inputs. The fuel system also gets new sensors via a fuel pressure sensor and a fuel temperature sensor and a second EGT probe has been added, mounted into the new fully-shielded exhaust silencer. By varying the fuel & oil delivery, ignition timing and power valve opening the new ECU maintains a tighter control over the engine’s operation to provide a smoother powerband, excellent torque and power with exceeding reliability. Cold seizures, over heating, detonation issues and under fueling are all but eliminated with the powerful programming and controls. The user experiences great power in all conditions, and is alerted if there is a performance or running issue that requires attention or intervention.
Fuel is delivered into the transfer ports, making this a semi-direct injection, or transfer port injection, system. Air rushing up into the cylinders from the crankcase carries the atomized fuel as it is injected. Using this kind of injection design does several things – it allows the use of lower pressure (and lower cost) injectors, as we have many more degrees of crankshaft rotation to inject the fuel compared to a direct-injection system. Maybe not as clean as a full DI system, but the SDI system is still quite clean and meets all EPA regulations, and really does extremely well in terms of efficiency and fuel consumption.
A new power boosting regulator, introduced last season on the Polaris Titan models, helps with faster startups and better power supply at idle or lower RPM’s. All of this is aimed at helping the machine deliver better running consistency and performance. The power is transferred through a new drive belt that has been designed specifically for the demands of the 850 powerplant – so your old Polaris drive belts for the 800 will not fit.
How much power does this new engine produce? Polaris representatives would not quote a specific number, but simply smiled and stated that it would be “The most powerful 2-stroke engine in the industry” and that it would be “enough” to do what was expected of it. We were also told it would provide the industry’s best power-to-weight ratio, coming in 9% higher than any other (in short track sleds) and 7% better in mountain sleds, and that the rotational inertia was 13% lower than the competition – meaning it would rev up faster and reach full power quicker. Early dyno testing indicates power levels of 168-169 HP, making this a strong package indeed.
In our own test rides and side by side comparisons with the competition we have to agree and confirm these statements, at least when using the pre-production engines we had access to. It should be making 165 HP (or more) based on these parameters, but we want to wait for actual production engines before making any solid proclamations. It is a smoother power delivery, being more linear than what we’ve come to love from the Liberty 800 that has a strong midrange hit. The 850 is deceptively smoother, but very strong and very fast. Those worrying about a first-year engine have been assured of the durability by Polaris providing a four-year warranty, a bold statement as to their confidence in this new engine package. We would be shocked if this isn’t the very best engine Polaris has ever produced, as it should be the most reliable and durable, as well as most powerful.
Specs and Additional Details on the 2019 Polaris 850 Patriot Engine:
All-new, “clean-sheet” design builds on 25 years of Polaris Liberty engine heritage
Unmatched durability proven through extensive testing in labs and on-snow
Guaranteed quality: standard 4-year warranty at no extra charge
In trail sleds: ferocious acceleration
In deep snow sleds: instantaneous lift
Low inertia and quickest revving
Light and flickable feel in all riding conditions
Industry-leading power-to-weight ratio
Unmatched throttle response
Designed for Power and Durability
Increased power but retained responsiveness while ensuring world-class durability.
Real-world performance based on 25 years of Liberty engine experience
Bore and stroke selected for lowest inertia and best real-world performance
Less inertia = Best throttle response and industry-leading handling
New Piston is optimized for reliability and durability.
+8mm compression height
+3mm thicker dome
More contact area with cylinder bore to maximize heat transfer
PVD-coated steel single-ring design
High-capacity wrist pin
New Lightweight Crankshaft
New “Clean-Sheet Design” crankshaft is strong and stiff while maintaining low inertia.
Larger clutch taper for durability and serviceability
High capacity bearing and pin design
Separate crankpins feature high grade steel (Case Carburized SNCM 420H)
New Cylinder & Cylinder Head
Cylinder and cylinder head designs optimized for cooling effectiveness.
Advanced Cooling System based on Computational Fluid Dynamics, which results in high velocity coolant flow around cylinder bore, combustion chamber, and exhaust valve
A 6-bolt cylinder structure was optimized through Finite Element Analysis and features a patent-pending exhaust port design featuring high-flow intake and exhaust ports for top engine performance and complete combustion
One-piece head design allows for structural rigidity, engineered coolant flow, and optimized weight
Patent-pending combustion chamber design allows for complete combustion and ultimate performance through entire operating range
New Water Bottle with Integrated Thermostat
Water bottle integrated thermostat maximizes durability and cooling efficiency
Patent-pending simplified, integrated thermostat design minimizes vibration and maximizes thermostat life
Self-bleeding cooling system
100 degree T-stat
Integrated by-pass for fast warm-up
New Engine Mounting
New engine mounting system seamlessly integrates into AXYS chassis.
Minimizes vibration transmitted to rider
Provides more consistent center distance to maximize belt life
New Throttle Body & Throttle Position Sensor
New, lightweight throttle body features a lightweight, simple, durable design.
Features a contact-less TPS for reliable, consistent performance
Permanent set – No adjustment required
Peak Electrical Efficiency
Power-boosting regulator for quicker starting; delivers maximum electrical power at Idle/Low RPM
Electrical ECU with faster processor, exhaust valve control integration, and greater input/output
New 3-Stage E-VES-II Exhaust Valve System
Features a simplified coplanar valve with fewer parts and an EV base that is lightweight, die-cast magnesium
Improved fit and sealing to the piston and exhaust ports to control exhaust flow and optimize performance
Optimized water jacket and valve cooling
Integrated cooling with no external lines
Premium, Integrated Design & Components
New exhaust system – pipe and resonator – improves flow and sound quality; EGT in full heat-shielded resonator improves calibration control
New wire harness routing for reliability and serviceability
New fuel system temp and pressure sensor is an industry-exclusive, patent-pending design that optimizes piston durability, increases control of variability in fueling, improves starting in all conditions, improves diagnostic functionality for easier serviceability, and enhances engine protection modes in the case of low fuel pressure
New, drive belt designed specifically for the 850 Patriot is optimized for durability and longevity
New VForce reeds designed specifically for the 850 Patriot feature carbon fiber petals for ultimate performance, and industry-exclusive secondary seal on the inner cage for maximum durability