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Snowmobile Fuel System: How to get the most out of your sled!

Upgrading your fuel system can result in more power and more protection. Run more boost with more fuel demand. Run cooler intake air temperatures. Fuel system upgrades make your machine more capable and more versatile.

The fueling system on a modern snowmobile has a few variations, but in most cases, the ECU is controlling fueling using one set of injectors (two sets on Ski-Doo). For this example, we'll discuss a Polaris AXYS 800 with a base-kit fueling system. Other kits may have some variations.

Agility for AXYS 800, until model-year 2021, comes with a base-kit fueling system, meaning this kit re-drives the OEM fuel injectors, only. Our electronics control this process. However, this system is limited by capacity. The OEM designs the injectors for a certain power-level (how much fuel can be used), with some percentage of additional capacity.

At higher elevations, a naturally-aspirated engine has less air, and therefore, consumes less fuel, and uses less of the injector. This is a portion of the reason why 'boost' works at elevation on the OEM fuel system in most circumstances. At low elevation, even very low boost conditions will likely require more fuel than the stock injectors can deliver.

Another feature of the stock injectors is that in response to the engine-environment, the ECU will call for fueling (and other) changes. In some cases, the ECU may sense pre-ignition or detonation, at which point the ECU will correct by adding more fuel (along with other feedback mechanisms). It is important to us that we allow the stock injectors to have available duty cycle to respond to these corrections, which helps prevent motor failure.

Our engineers recognize fuel-system-sizing as a critical part of turbo-kit design. We sell our kits with guidelines to help you prevent over-demand of the fueling system. BoonDocker kits that come with a base-kit fueling system are suggested to stay above 5,000 feet, and to not exceed 8.5 PSI of boost at 10,000 feet, or more accurately, 18.5 psi absolute pressure.

As you can see, it's possible and common to exceed the capacity of the OEM-designed fueling system (base-fueling). Exceeding the capacity of the fueling system is asking for trouble, and can lead to a broken motor.

In our upgraded fuel system (generally), we utilize an auxiliary set of injectors, located in the charge-air box (or on Ski-Doo, we use larger auxiliary injectors in the boost-port), to supply the extra fuel demanded. With this upgrade, our electronics control BOTH the auxiliary injectors AND the stock injectors. We create our tune(s) with available duty cycle on the stock injectors to respond to ECU needs.

An additional feature of the auxiliary injectors is that they spray cold fuel, directly through the throttle bodies, into the case. There has been observed a cooling effect of this manner of fuel delivery, which can also create more power and possibly more consistent runability.


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