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Tuning became more of a challenge in the late 1980's when Polaris introduced its top-of-the-line RXL 650 triple with electronic fuel injection.
Prior to that, the RXL had become a favorite of performance hungry sled modifiers. All an owner had to do was install a set of triple pipes and the RXL jumped up 20 hp. Sure, you had to install new clutch parts and richen the jetting to feed the extra 20 ponies more fuel, but changing these parts was easy.
Imagine then, the confusion when Polaris installed EFI on sledders' favorite hop-up machine.
Most tuners' big concern was how to adjust the EFI for more fuel flow when installing high-performance parts. There were plenty of engine masters with fuel injection experience available for consultation, but for a price. Finally, four separate aftermarket companies chipped in to get a solution from FMS (Fuel Management Systems), a small consulting company with experience in the outboard motor market.
EFI and fuel flowThere are several ways you can increase fuel flow with an EFI system. You can install an adjustable pressure regulator, and increase the supply pressure, or you can install higher flow injectors. You also can tap into one of the tuning signals, like the air temperature unit, and make the computer think it's seeing a much colder temperature.
The problem with all these methods is that they richen up the complete fuel curve from idle to top end, and when the total fuel flow is richened, the idle and mid-ranges become too rich.
The solution from FMS was a complete new software program that replaced the stock chip. EFI programs are located in the EFI chip, so aftermarket companies could now offer a new "power chip" that matched their modifications. All the pickups and the original hardware stayed the same, only the chip was changed.
Developing this chip to work with the mods took a lot of time. At Aaen Performance we ended up programming and testing more than 100 chips to perfect ours. We did mountain testing, plus cold-start tests at -30°F too. Clearly this was not something the average snowmobiler could do on a weekend.
My firm also tried to sell EFI racing systems, but this was a dismal failure since the process of tuning was way too complicated. Although our seasoned racers won with fuel injection systems, everyone else eventually preferred to change jets on a simple carburetor.
It did not make things any easier when the factories changed to EFI boxes where the chip was "baked" into the box and covered with silicone so you could not get at it. Worse yet, fuel pumps and pressure regulators were buried in the fuel tank, so changing the pressure with an adjustable pressure regulator also became difficult.
EFI disappears, but returnsPolaris dropped its EFI models in the 1990s, and for a while Arctic Cat was the only company offering fuel injection. Eventually, Cat also gave in and began offering its most popular models with carbs, in order to satisfy performance enthusiasts, who were among its most loyal buyers.
Suddenly it seemed that fuel injection was on its way out. But then demands for cleaner engines to meet emission standards brought electronic fuel injection back again. This time it was Ski-Doo that introduced its clever (SDI) semi-direct injection. SDI has two injectors spraying into the back transfer ports after fresh air has entered the cylinder.
So EFI or SDI appears to be the wave of the future, as EPA regulations will dictate their use on most snowmobiles. But there's good news for those of us who enjoy tweaking our sleds to boost power. Tuners are getting ready with a new line of products to reshape the fuel delivery curves.
EFI tunersSnowmobiles are not the only recreational vehicles to have a need for EFI "tuners." Cars, motorcycles and ATVs need them too as emissions requirements have invaded their territory.
Today there are several key players in that growing EFI market. For instance the "Power Commander" by Dyna Jet and the F.I. Controller from Dynatek are two sophisticated units available for motorcycles and ATVs, but these companies have not yet entered the snowmobile market. However, two that are building units for us sledders are Boondocker and Dobeck.
Boondocker developed its system to control the fuel flow to its nitrous oxide injection system. The Boondocker system uses input signals from the original EFI harness to operate a separate computer box that is plugged into the system. The software in the box can then add or subtract fuel to the signals from the original EFI box.
If you disconnect the Boondocker box, the EFI goes back to the original calibration. Each Boondocker box is supplied with base curves for the model it's intended for, and there are 4 distinct rpm ranges to choose from. On the box for the Arctic Cat F7, the ranges are 3,000, 5,000, 6,700 and 7,800 rpm. Each rpm range then has a value for low-, medium- and high-throttle position settings and a trim setting, where the clutch side cylinder can be enriched for running with twin pipes.
All the adjustments can be done simply on the system by moving values around with up and down buttons. In addition there is a whole different setup for the nitrous operation. No computer is needed to make the changes, you simply push buttons on the unit.
Mark Dobeck, founder of Dyna Jet and the same person who brought you "Jet Kits" and the Inertia Dynamometer, now brings you the "Electronic Jet Kit." He has spent a lot of effort developing a simple system that tunes like a carburetor. Dobeck offers a number of systems for motorcycles and ATV's, but has decided to work closely with performance companies in the snowmobile industry.
Dobeck offers several basic tuners that each company can tailor to its special products. These products can range from sophisticated turbos, superchargers and nitrous systems, to tuned pipes or simply fine tuning for stock machines.
A basic Dobeck box has a minus and a plus button, a mode button to change rpm ranges and additional modes for anything from turbos to nitrous. Boss Industries, Mountain Performance, Pure Logic and Hauck Performance are a few of the performance firms using Dobeck units. Getting into all the intricacies of turbos, superchargers and of nitrous oxide will wait for future stories, but we talked to Pat Hauck about the function of his basic box for a Yamaha Apex.
By hitting the mode button, different lights come on. The green light means you are in light-load mode, from idle to part throttle operation. A red light means you are in the main circuit, richening mid-range and top-end. With the yellow light on, you are adjusting acceleration response to remove any hesitation or flat spots.
With the unit mounted on your sled all you have to do is push buttons to enrich the different torque ranges.
How do you know when you are dialing in on the right combination? There are several procedures; the simplest is the oldest, just by running the machine and checking performance.
Hauck's box only allows you to richen the base curve; the negative button is only used to back off when you went too rich. Otherwise you stand the chance of leaning the curve out too much.
You can, of course, use exhaust gas temperature meters (EGT) or oxygen sensors. Hauck prefers using oxygen sensors to dial in his 4-strokes by keeping the mixture at 12.5.
On 2-strokes oxygen sensors can get oiled up and lose accuracy, depending on where on the pipe they are mounted. So an EGT gauge may be preferable.
Both Boondocker and aftermarket companies using Dobeck units can now offer a simple way to tune the EFI when adding performance parts. This should finally remove most questions tuners have about modifying fuel injection sleds.