Arctic Cat C-TEC2 800 With Dual Stage Injection Arctic Cat C-TEC2 800 With Dual Stage Injection
The successor to the mighty Suzuki 2-stroke 800 twin has arrived – Arctic Cat’s all-new C-TEC2 800 2-stroke twin with Dual Stage Injection. We’ve... Arctic Cat C-TEC2 800 With Dual Stage Injection

The successor to the mighty Suzuki 2-stroke 800 twin has arrived – Arctic Cat’s all-new C-TEC2 800 2-stroke twin with Dual Stage Injection. We’ve been told for years by our friends at Arctic Cat that the days of carbureted and throttle-body injected two-strokes was coming to an end. The EPA emissions regulations that started in 2006 have slowly been getting tighter. Here we are at the 2018 model year and we now realize all of the incredible benefits of the long wait.

By Kevin Beilke- SnowTech Central with Ryan HayesArctic Cat 2-Stroke Snowmobile Engine Group

Instead of taking the route of direct injection, Arctic Cat has stayed true to their core and continues with their own technology; Dual Stage Injection, first introduced for 2014 in the 600 DSI engine package. Arctic Cat is now flexing their muscle with their DSI technology, as DSI uses low pressure injectors and is less complex and less expensive than direct injection yet delivers many of the same benefits.

Arctic Cat C-TEC2 800

The C-TEC2 800 is the first “clean technology” 800 twin 2-stroke engine from Arctic Cat. The 8000-Series 799cc C-TEC2 with Dual-Stage Injection features batteryless EFI; electric oil pump; APV electronic exhaust valves; Exhaust Pipe Temperature System (EPTS); knock sensor; and engine reverse technology. It’s exceedingly robust, lightweight and allows Arctic Cat to meet Tier III EPA regulations for emissions.

This is the second 2-stroke snowmobile engine designed engineered and produced entirely by Arctic Cat and has been under development for eleven years, back to when the first (600) DSI engine started. “Every component of the C-TEC2 800 was designed and sourced by Arctic Cat,” said Donn Eide, Snowmobile Engine Design Manager at Arctic Cat. “(Like the 600), the 800 DSI uses the same clean-sheet design incorporating both new and existing technology pioneered by our team of engineers.”

Arctic Cat C-TEC2 800

The C-TEC2 800 will be assembled at the Arctic Cat engine facility in St. Cloud, Minnesota, using components sourced globally. This 61,000 square-foot facility continues to grow, and is now taking on assembly of an off-road engine for Textron from a plant outside of Berlin, Germany. They’ve been assembling Arctic Cat ATV engines since 2007, with the C-TEC2 600 being the first snowmobile engine to roll down the line in 2013 (for model year 2014 sleds).

Perhaps some clarification is in order. DSI dual stage injection is NOT direct injection (where fuel is only injected after all ports are closed) nor is it transfer port injection (like the Polaris CFI or Ski-Doo SDI where the fuel is injected into the transfer ports and clean air from the throttle bodies enters through the crankcase and rushes up through the transfer ports, carrying the fuel up into the combustion chamber). This is not a crankcase injection system either, as the injectors are mounted into the sides of the cylinders, allowing them to inject the fuel both on top of and inside of the pistons. Inside of? That’s what makes this so different.

Arctic Cat C-TEC2 800

Arctic Cat analyzed what kind of fuel injection systems could be utilized on a two-stroke snowmobile engine and they chose the route of using low-pressure, lower voltage injectors than what the Ski-Doo E-TEC direct injection engines use (which are high pressure injectors driven by higher voltage systems that admittedly add cost and complexity, but can execute the injection process much faster when the ports are closed so they are true direct injection and cleaner because of it). Since the Arctic Cat Dual Stage Injection system is lower voltage and low pressure injectors, they need more time at higher engine RPMs to get enough, or the required amount, of fuel into the engine.

Time is precious when injecting fuel. High-pressure E-TEC injectors have very little time to get all of the fuel into the cylinder once all of the ports are closed, that is why they have to be at such higher pressures to get enough fuel in there in such a short time. With Arctic Cat’s DSI system, since they are using low pressure injectors they needed more time. At lower engine speeds and power levels there is enough time to get the required amount of fuel in there by injecting right onto the top of the piston. But, as engine speed and power increases we run out of time to get enough fuel in there at low pressure. Hmm. What to do. Why not put a slot in the side of the piston right where the injector is, so as the piston dome comes up past the injector it just keeps right on feeding fuel? This sure gives us a lot more time to work with! Brilliant!

Arctic Cat C-TEC2 800

Arctic Cat C-TEC2 800

In the C-TEC2 engine the injectors are positioned on the rear cylinder walls and actually fire through the cylinders. Their location is very specific to the timing of the piston and its slot to be able to inject the fuel at the right times and in the right amounts. At lower engine speeds the injectors are firing the fuel down onto the top of the hot piston as it rises for great fuel atomization. As engine speeds increase the injectors stay on and fuel continues to be sprayed through the slot in the piston. This is where the term “Dual Stage Injection” comes from, in that fuel is entering the engine on top of the piston at low speeds and also through the piston slot at higher speeds.

Arctic Cat C-TEC2 800

Arctic Cat tells us this approach was selected as the better balance between many factors, including weight, clean operation and fuel consumption, all with less complexity and cost. These are lower-cost low-pressure fuel injectors operating at 58 psi, powered by a standard low voltage electrical system. These features help keep the DSI system simpler and less expensive in comparison to the high-pressure high-voltage injectors found on E-TEC direct injection systems that require a beefier magneto to produce the higher voltages required by the “voice-coil-style” E-TEC injectors.

While we would expect The C-TEC2 to be higher in unburned hydrocarbons in comparison to the Ski-Doo E-TEC engines, we’re told it will be lower in CO emissions with “comparable fuel consumption and miles per gallon”. Arctic Cat also indicates this engine will be lighter, specifically a lighter magneto since they do not need to generate the higher voltages for high pressure injectors (20 volts DC vs. 55 volts DC).

Arctic Cat C-TEC2 800

Injecting fuel through the slot in the piston does many things. It gives us the time to get enough fuel injected at low pressure but it also has the great benefit of cooling. Fuel is a great coolant, and feeding fuel into the crankcase through the slotted piston cools the bottom and inside of the piston and it cools the entire crankcase. A cooler running engine typically last longer.

So, one might wonder what happens to the piston rings in the area of the injectors as the piston passes the injector. The injector doesn’t turn on and off as the rings pass by, it comes on and stays on at high speeds so it is injecting first on top of the piston and then through the slot as the piston rises. Won’t this wash the oil right off of the rings and ringland? Not a problem if there is some oil mixed with the fuel!

Some of the injection oil is mixed with the fuel in the injector rail before the fuel is injected. This is especially beneficial to lubricate the rings as the piston passes by the injector. Another benefit is the ability to better lubricate the piston pin bearings and rod bearings, something Arctic Cat engineers were quite proud of, claiming this to be an advantage of their design in being able to provide better lubrication.

Arctic Cat engineers had pistons on hand for us to examine that had 6000 and 9000 miles on them so we could see firsthand the lack of wear, and there was in fact very little wear on the moly coating. They seem quite confident that this system will provide far greater durability in terms of piston and ring wear than other injection systems, and believe the piston and crankcase cooling will be superior as well with this design, as evidenced with the durability of their C-TEC2 600 after four years of production.

Arctic Cat C-TEC2 800

We’re told this new engine will produce enough heat-soaked HP to be right there with the Polaris 800 and even run with the Ski-Doo 850, especially at higher elevations. SnowTech riders have already logged over 2,000 miles on the new 800 engine package and can validate the power as being smoother in delivery, almost sneaky in how linear it is, and easy to use to your advantage. Maybe not quite 160 HP, but pretty close. Once broke in it should be slightly stronger than a stock Suzuki 800, but it takes a while to loosen up as we had over 800 miles on our test unit before we saw full power. It is an exceptional performer at higher elevation, something we learned with the extended riding season that went into late April, May and June. Arctic Cat was able to spend extra time working on the calibration and set-up and told us it was working extremely well and that they were very pleased with the results.

This new engine does want to be running 91 octane non-oxygenated fuel. It is equipped with a knock sensor so it can adjust fuel delivery and ignition timing as needed for safe, knock-free operation as conditions and fuel quality varies. There are three ranges of measurement in the “Fuel Judging System” where, if detonation is detected, the system will first pull back the timing advance. If knock is still detected, it will then adjust with even less timing advance in addition to increasing fuel. If knock is still there, the system will go through a final round of less timing advance and increasing fuel before the fail-safe mechanism is finally activated to prevent engine damage and the system moves into limp mode.

Another feature that helps with the throttle response and power output would be the “W” shaped reed blocks. This design allows for less lift of each individual reed, thus reduced reed fatigue. These reeds are made of a glass-fiber material, different from what was used in the Suzuki two-stroke engines. We still find three-stage power valves, similar to what was found on the 800 engine, and there is an idle air control solenoid to better control engine idle speeds.

This new engine features an electronic fuel pump and an electronic oil pump for better metering and a lighter throttle pull. The electronic oil pump is located in the oil tank and does not require bleeding of trapped air. It delivers a ratio of about 125:1 at engine idle and goes into 3-dimensional mapping for the rest of the engine operation. Where a mechanical oil pump would be operating at ratios of 40/50:1, this new pump will be working with ratios of on average 60-65:1 for reduced oil consumption and emissions. And as stated earlier, some of the oil is mixed with the fuel in the fuel rail right before injection so this system does a better job at lubricating the piston pins and rod bearings, but was really critical to lubricate the piston rings due to the injector positioning. The rest of the oil goes into the throttle body airstream, and is one of the reasons we are being encouraged to use the C-TEC2 oil designed specifically for the DSI technology, as the ratios are going to be leaner and the lubrication requirements more stringent.

The introduction of the new DSI 800 engine is exciting not only for Arctic Cat fans but for the industry as a whole. This simpler approach should help to keep costs in check, while meeting Tier III EPA emissions requirements. We have yet to see the exact emissions numbers but would logically expect it to be higher in unburned hydrocarbon output than an E-TEC, but who buys a snowmobile based on EPA numbers? We buy a sled for the power, reliability and performance it offers, hoping it will do so with good fuel economy and run smoothly without emptying the oil tank. Despite recent advancements in four-stroke snowmobiles, the good old two-stroke is alive and well, lighter and more responsive. It might not last as long as a four-stroke but the power to weight ratio is an undeniable advantage, as it always has been.

Sidebar:

INSIDE ARCTIC CAT’S DSI
(DUAL STAGE INJECTION)

Arctic Cat has been using a version of the C-TEC2 motor in the 6000 series machines the past four model years. We are familiar with the technology Arctic Cat is using here, but the new 8000 series motor benefits from what Cat has learned and incorporated a few improvements.

The motor is still a lay-down style engine like the previous Suzuki version with the exhaust and intake positioned on the “front” side, or top of the motor, with the injectors and fuel rail on the back side. Bore and stroke remain at 85mm x 70mm but that is where most similarities end with our beloved Suzuki 800. Unlike the previous 4 spark plug design, a new head utilizes the more conventional single plug per cylinder system and the combustion chamber shape is completely new. A new exhaust valve system has some resemblance to the previous version utilizing a traditional guillotine style main exhaust port but Cat is now controlling the boost ports as well with rotary style cutaway valves that are mechanically connected to the main valve and open simultaneously. The ECU utilizes one of several maps to place the valves in one of the 3 available positions to create a seamless transition and smooth power delivery. So seamless and smooth that it is almost electric-like.

Intake air is fed through larger 50mm throttle bodies connected to “w” style (think V-force style) reed cages. Fuel is no longer injected into the throttle bodies but rather a semi-direct intake port injection system located on the opposite side of the cylinder (single injector per cylinder). Oil is also injected into the fuel rail allowing oil and fuel to be injected into the top end simultaneously. We are not aware of any other manufacturer injecting oil into the fuel rail, so this is a unique feature to Arctic Cat.

Although other manufacturers have used semi-direct injection, none have used what Arctic Cat calls Dual-Stage Injection (DSI). Here is how it is unique: The piston has a slot cut into the skirt directly in front of the intake transfer port which allows the injector to deliver the fuel/oil mixture at any point in the stroke.

The two stages are as follows:
1) The ECU can control the injectors to deliver the fuel/oil mixture based off piston location. If the mixture is delivered when the piston is below the injector, the result is cleaner emission through the lower cruising throttle positions than compared to the previous throttle body injection system.

2) When the injectors are allowed to deliver fuel/oil through a longer part of the piston travel, the mixture of fuel and oil will also spray to the underside of the piston and will be directed at all of the moving top end parts. This will make for better lubrication and cooling which can also make for improved power.

Arctic Cat C-TEC2 800

An electronic oil pump mounted to the bottom of the oil reservoir replaces the previous mechanical unit that was mounted to the crank case and gear driven off the crankshaft. The ECU controls the new oil pump and uses several inputs such as throttle position and RPM to determine how much oil the injection system needs to deliver. Not only is oil injected into the fuel rail, it is also injected into the bottom end to help lubricate the crankshaft. Arctic Cat claims a 30% reduction in oil consumption below 7000 RPM. Less oil consumption is always a welcome improvement. The previous Suzuki 800 is known for being very reliable and Arctic Cat claims the new lubrication system improves on what was already a good system.

A new ECU with a quicker processor was required to help support the added functions of the motor and injection system. The number of flywheel pickups was increased to help feed more accurate crank position information to the ECU.

Arctic Cat matched the new motor to a new tuned pipe and stainless steel Y-pipe while utilizing the same stainless steel silencer as the 2016 machine. Optimum engine RPM for best performance is 8200-8250 RPM with peak engine horsepower landing slightly higher than its Suzuki predecessor. The real gain is in the midrange (5,000 to 6,000 rpm) where power is increased as much as 8 horsepower and torque was increased by 18%. Bottom end torque (below 5,000 rpm) is much better with a claimed 36% increase over the previous motor, and this is what most riders will immediately feel off the line.

This new engine does have an electronic break-in program, where peak RPM is limited to 6,500 rpm during the first 20 minutes of running time. Fuel delivery is 4% richer, but the oil pump is cranked up to a 10:1 ratio for initial break-in. Owners might want to run their new engines through a couple of heat-cycle warm-ups, letting the sled warm up and cool down a couple of times to burn through this 20-minute limiter period before you actually ride it. Otherwise, if you pull off into deep snow during the first 20 minutes you won’t be able to power out of it as you will still be limping at 6,500 rpm.

For the next 5+ hours (6-hour total break-in period) the engine will not be RPM limited, however the fuel delivery will be richer by 2% and the oil pump will also be running rich at a 30:1 ratio. During this time we suggest you carry extra oil, as we burned through quite an amount during high-mile rides in this period. You might not have enough oil to make it home, we didn’t, but we were running it 250+ miles that day.

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