BIG Power & Greater Agility
By Dustin Pancheri & Jerry Mathews – SnowTech Mountain
The speculation and rumors are finally put to bed; Polaris will offer a new 850cc two-stroke in their 2019 lineup and it will be available for every segment from short track to long. For the mountain guys the news couldn’t be more exciting. Elevation eats horsepower so the enticement of an 850 makes us feel like a hungry dog that can smell fresh meat. And now that we have spent some time on several different versions of the machine we can tell you that the meat tastes good and we want more.
2019 Polaris 850 Pro RMK 174″
The New 850
First off, this is a clean sheet, all-new motor from the crank to the ECU. This means that virtually every part on the 850cc motor is new. In fact, you can count the number of parts it shares with the 800-liberty motor on one hand. This is significant because it allowed Polaris to dictate design goals centered around performance and durability derived from the latest technology rather than goals that required the use of existing hardware which is likely old technology.
To start, the new crankshaft has a longer 74mm stroke and features a larger clutch taper with high capacity bearings. It is mated to new lightweight 85mm pistons and although they are the same bore as the 800 motor the new pistons are a single-ring PVD coated design with a 3mm thicker dome and are 8mm taller on the compression height. Polaris told us they experimented with several different bore and stroke combinations hitting the snow with each version to test responsiveness and power delivery. In the end this combination gave them the best combination of throttle response, torque and horsepower and a power delivery that was smooth and manageable.
A new 6-bolt monoblock cylinder was 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.
Polaris stayed with the one-piece head design as they feel it is the best for structural rigidity, but the shape is different and has a new patent-pending combustion chamber to work with the new engine properties. A new thermostat design is also patent-pending and has been integrated into the coolant bottle to reduce vibration and maximizes thermostat life. The system still utilizes a bypass and is set to open at 100 degrees.
A new engine mounting system is used to harness the entire package to the AXYS chassis which means you won’t be dropping an 850 into the 800 chassis. New VForce reeds designed specifically for the 850 are mated to new throttle bodies bring air in and utilize a new contact-less TPS for reliable, consistent performance. The throttle bodies are permanently set which means no more recalibrations to keep your TPS settings accurate.
Engine management is controlled by a new faster ECU which receives information from all the standard sensors but new also gets info from a few new sources. A second EGT probe has been added and can be found mounted into the new fully shielded exhaust Silencer. The Fuel system also gets new sensors via a fuel pressure sensor and a fuel temperature sensor. A new power boosting regulator helps with faster startups and better power supply at idle or lower RPM’s. All of this of course is to help the machine experience 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.
AXYS React
Polaris kept most of the AXYS chassis the same except for the new React front suspension. The new 36”-38” ski stance utilizes new geometry with forged aluminum A-arms and spindles. Suspension travel is the same, but the shocks now come with SLS shock springs which are 3 pounds lighter. Polaris claims that they are even lighter than some titanium springs.
It all culminates into a more powerful, easier to maneuver machine and for us we could feel the difference in the first 30 seconds of riding it. The machine is noticeably more powerful through the entire powerband. The surprising thing to us though is just how smooth the engine is and how controllable the power delivery is. The engine does not vibrate, and the throttle almost feels like it is attached to an electric motor. We never felt the exhaust valves open or close and we had to listen very close to the exhaust note to even hear them change.
Ride Impressions
The motor makes more torque down low and carries it through the mid, then continues to pull through to around 8200 RPM. The power transfer is smooth with no harsh engagement or “hit”. This really surprised us because let’s face it: in the past most long strokes motors were hard to handle, they vibrated and the power hit hard of the bottom but Polaris did an excellent job at delivering a smooth manageable power.
The suspension changes made the machine very quick to respond. This took a few minutes to get used to as we did over ride it a bit using too much body input to initiate some maneuvers. It does not require much energy to change direction which is good and will let the rider save energy. We had to re-train ourselves to move around less as it wasn’t necessary to swing a leg from one side to the other as much as the wider front end. The chassis is fairly stable with the narrower front end and sticks to a side hill just like the wider front end.
We rode it in several conditions over the 3 days and it stayed predictable in almost every condition. The narrow front end was surprisingly stable down the trail which we did not expect. Most narrow front suspensions sacrifice stability and get twitchy, but the new geometry kept the predictability that the AXYS has offered in the past. Some riders may choose to adjust the skis to the wider position if they like the feel of the wide front end but riders who spend much time cutting across steep slopes and through tight trees will probably like it narrow. From what we can tell ride quality is exactly the same as the previous AXYS machines which is decent, however we would take the piggyback shocks over the monotubes to get the extra adjustment.
The cockpit is unchanged from last year so if you like the riding position that the AXYS has offered in the past you will like the 2019. We prefer the mid height bars and feel like most riders will feel the same. The machine has virtually no storage and although the Snow Check versions will come with some bags we feel like this should be standard as every machine should come equipped with a place to keep safety equipment and a few spare items of clothing.
We prefer the 163” 2.6” series 6 track for most conditions as it is the most versatile when conditions change and also because we like how responsive the Quick Drive system is. The taller 3” lug does hook better in deeper snow conditions so those that spend most of their time in the bottomless fluff should consider the 3” with the chaincase.
Verdict
Polaris clearly did their homework with the new 850 engine and if the production version is anything like the pre-productions we have been riding consumers will be more than ecstatic. The torque and power of a big bore with the throttle response and rev of a small block really is the best of both worlds. The 850 will only be available as a Snow Check model which means you won’t get one if you don’t order it on Snow Check this spring which ends April 17th. Oh, and don’t forget about that 4-year warranty!
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