We waited a long time for this new engine from Cat and the most tempting part was it had an excellent model preceding it, the 600 CTEC-2. Naturally, we were expecting greatness from it.
The key element to keep in mind with this engine is the difference in the way it lubricates its bottom end compared to the squeaky-clean Ski-Doo E-TEC.
Ski-Doo’s Direct Injection technology on both the former 800 and 600 allowed no fuel or oil mix into the crankcase (although the new 850 actually does have a pinpoint oiling system) and lubricates the sealed bearings down there with a special permanent grease.
In the Arctic Cat DSI, which stands for Dual Stage Injection, the injectors are located on the cylinder (not in the transfer port) and inject oil and gas mix onto the top of the piston as it’s moving to bottom dead center.
When the piston is at top dead center again the injectors spray oil and gas mixture into the crankcase through the slot machined into the side of the piston. Thus DSI allows gasoline to cool the bottom end and oil to lube it at the same time.
This makes for great reliability but it’s harder to get super-clean EPA results with any 2-stroke allowing fuel into the bottom end.
Good results are accomplished on the DSI with very precise fuel and oil monitoring from an electronic oil pump and tight EFI calibration.
Since fuel and oil are being injected into the crankcase and not just randomly scavenged like on the old 800, amounts can be regulated to a very lean condition without damaging the crank or rod bearings.
The cylinder walls and piston rings are carefully lubed the same way by the mixture being transferred onto the top of the piston.
Cat has been able to maintain excellent durability with this design and because of its precise fuel metering, is both EPA clean and offers a much more responsive tip-in at the throttle.
The net result is more torque at low speeds and comparable top end at the end of the lake.