Here is a review from Pockets with some good detailed info.
"The other big news is a new Patriot 850 twin engine! This will be an option across the line, in all models which have the 800 now. But, IT WILL ONLY BE OFFERED DURING SNOWCHECK! This is an all new engine, not just an upgraded 800 Cleanfire HO. It only shares a few bolts with the 800 HO. Before I expand on that, there are also a few other improvements related to the engine, and from what I remember, some of them will be implemented across the line with other engine packages.
Polaris has changed the placement of the thermostat, removing it from the engine, and placing it in a newly designed coolant overflow tank. It is designed to maintain an engine operating temp of 100 degrees, for the best performance, and has a goal of consistent running temperatures. The engineers found that over time, the constant vibration of the engine would affect the thermostat, causing inconsistent opening/closing, as well as wear leading to failure. In riding the new 850 engine equipped models, I never saw over 125 degrees even in some icy low snow trail conditions.
The motor mounts have been completely redesigned because of a combination of customer feedback concerning vibration and performance inconsistency, and to ensure the power of the new 850 is properly transferred through the driveline. All 4 mounts resemble the old style large diameter puck mounts, with a central stud. The PTO side torque arm has been eliminated, and instead the rear motor mount is placed in such a way that it controls the rearward movement of the engine. The wide underside of the round mount and central stud, are inline with the rearward movement of the engine. The other 3 mounts are also mounted this way, with the stud and flat surface in line with the direction of engine movement under load. The aluminum bracket which the mount attaches to also has a raised portion, which encapsulates the rubber puck, so that it cannot expand to a larger diameter than designed under load. The vibration reduction with the new mount system was substantial. The ski tips didn’t dance at an idle, there was no feedback through the handlebars, seat and running boards. You could feel the difference while riding as well. This was compared to models which had the 800 HO engine and old mounting system. Vibration in the 600 engine equipped sleds was on par with the 850.
The entire wiring system under the hood has been simplified and rerouted for best serviceability. Instead of wiring being zip tied to contact points, there are specific tabs on the frame, and clips which attach to them. This will prevent improper routing after service, and the chance of a mistake being made on the assembly line. The relays and such are placed in a centralized “fuse box” for better protection and access.
One improvement the new 850 engine brings to the electrical system, is the change to one coil which will send power to a main distribution hub which the separate systems will draw from. Previously 3 coils in the stator generated power for the 3 main systems independently. Ignition, fuel system, and lighting/other electrical. (if I am remembering correctly!). Now, the electrical is comparable to an automotive system, which has the alternator generating power and sent to one point, then distributed to the various systems. This allows the voltage regulator to respond faster to load changes, makes the entire system simpler and more reliable, as well as provides more consistent power which the ECU and fuel injection system need to operate at top performance.
Now, what most everyone has been waiting for, a new more powerful engine from Polaris, the Patriot 850 twin! As far as raw numbers are concerned, we were not given them, but were told a 10% increase in power over the 800 HO, with a much wider powerband. The new engine is all new, sharing nothing with the 800 HO. If this concerns you the engine has been in development for 3 or more years (I apologize I forget the exact number). This includes dyno testing and thousands of miles of actual in chassis riding. Polaris will also be offering a special warranty program for sleds ordered with the engine, showing their confidence in it, and to put customers minds at ease about buying a first-year engine package. They also tested many different bore/stroke/rod length variations, not just in the engine room, but in chassis, before choosing this configuration. This engine gave the best in chassis feel, as far as power delivery, noise/vibration/harshness, overall performance over a wide range of conditions, handling and reliability. The engineers said it was easy to make good numbers on the dyno, but many combinations did not make for a nice driving sled. You must know that everyone who works at Polaris, are riders and enthusiasts. The engineers log thousands of miles during the development process.
Some key points of the engine are;
-increased crankshaft diameter and assembly process to increase strength and reliability
-different clutch taper
-greatly increased PTO crankshaft bearing load area (wider and diameter).
-new piston design with much longer skirt to decrease piston slap
-cylinder skirts extend into crankcase deeper to give more strength and piston support
- “Shrink wrap” cylinder head water jacket design to increase cooling efficiency
-coolant flow through the engine is optimized for maximum power output and consistency
-new combustion chamber design for reliability with varying fuel quality. The spark plug and the cylinder head around the plug is extended into the chamber.
-new v force reeds
-new Dell Orto throttle body, with holes drilled in the throttle blades for idle air bypass. You may now adjust the idle rpm if desired without affecting the TPS baseline setting.
-new magnetic/hall sensor type TPS, no adjustment required or possible. TPS is synched during initial assembly.
-exhaust sensor in the main pipe and in the muffler, which allows the ECU to better determine fuel and ignition requirements.
-new simpler VES system design, with cleaner, more consistent operation. Also, better overall power as a result of better cylinder pressure sealing.
There are many other points to the new engine, which I am missing. One key fact which proves the power this engine makes, is that Polaris also designed a new drive belt for it. The primary clutch has 6-gram heavier weights than the current 800HO yet has the same suggested full throttle rpm. If you attribute 2 grams of the weight increase to the harder belt, 4 more grams at the same rpm means a lot more power is being made. I was not able to confirm any other clutching calibration."