Find us on Facebook Follow us on Twitter Check out our YouTube Channel

Polaris 850 Patriot dyno data!

DynoTech test on the new Polaris 850
Polaris 850 Patriot
Finally—the Polaris snowmobile powertrain engineering team got a “clean sheet of paper” by top management to bring its flagship big two-stroke twin into the modern age. And with that, Polaris shipped a zero-mile production Assault 850 Patriot to DynoTech Research in Batavia, N.Y. for our third-party independent engine dyno evaluation.

■ Carte blanche
Here is the successful result of five years of work by the engineering team, including Dallas Blake and Darren Hedlund who came to DTR for the break-in and dyno evaluation of our first production Axys 850, and to help us understand the all-new engine.

What’s really “new” on the 850 Patriot engine? Just about everything: Longer stroke, but still lightweight porkchop-counterweighted crankshaft (lighter weight = quicker throttle response), new crankcase, cylinder, pistons, head, larger 50mm throttle bodies; and a larger diameter tuned pipe and higher flowing, but lighter weight muffler, now fitted with a temperature probe. Muffler temperature is monitored for riders who might risk melting plastic when burrowing through powder at WOT for long periods of time. At that point, the engine will go into “protect-the-plastic” mode and cool things down perhaps with added fuel and lowered exhaust valves. The exhaust valves and servo are all new. Tighter valve clearances allow for even lower fuel consumption while cruising.
Polaris 850 Patriot
Patriot's HP is very close to that of the E-TEC 850, the only difference is the RPM where peak HP occurs. For the Polaris faithful, great progress has been made!
■ Better temperature control
Looking at the engine components that Dallas and Darren had displayed on the desk in the DTR control room, the most obvious difference compared to the previous Polaris twins is the now-diminutive coolant passages in the crankcase, cylinder block and heads. Shrinkwrapped! The large capacity, lazy flowing coolant passages in the early cylinders and heads are gone—replaced by modern, low-volume, extremely narrow coolant passages that promote higher velocity, more turbulent coolant flow that does a much better job of scouring heat from the cylinder bores and combustion chamber surfaces. Both the 850’s head and cylinder have 1/3 the coolant capacity of the 800s! Google a photo of a modern NASCAR engine block. Gone are the flat V8 block sides, replaced by shrinkwrap-appearing outer castings that mirror the four round cylinder bores closely on each side of the V. On the 850 Patriot, improved cylinder and head cooling can result in reduced likelihood of detonation and will help cool pistons and exhaust valves better than before. Add to that, a new lower temp thermostat begins opening at 92F then is wide open at 100F. Good!

■ The good news
The new single ring pistons still require heavy loading break-in to create optimal sealing and maximum horsepower. On this zero-hour engine, we picked up 5 to 6HP over 35 to 40 dyno sweep tests on Polaris VES synthetic injector oil.

The dyno session was done on a warm, humid day. Water in the air saps horsepower by displacing oxygen, and the ECU doesn’t compensate for it. After the engine break-in was complete, we fed 30F refrigerated dry air to the engine intake, and put four gallons of 30F (chilled in the 1,000 cubic foot refrigeration room) 91.4 R+M/2 octane pump gas with 3.8 percent ethanol in the tank. The ECU was taken out of break-in and left in max performance non-ethanol mode, which probably should be referred to as a “high octane mode” since due to its cooling effect and added O2, ethanol added to premium fuel is a good thing when it comes to making HP. Probably the only time to switch to “ethanol mode” is when you can only buy low octane ethanol fuel and experience detonation.
Want to leave a comment?
Only registered members of are allowed to leave comments. Registration is FREE and only takes a couple minutes.

Login or Register now.
Sign up for our free newsletter
By signing up you may also receive reader surveys and occasional special offers. We do not sell, rent or trade our email lists. View our Privacy Policy.