Arctic Cat issues
Here's a quick overview of some of my thoughts on the Arctic Cats, and tuning in general:
Twin pipes have sometimes been difficult to tune, or at least to get to run consistently (esp. with porting) due to several issues.
First of all, since these pipes generally increase the rpms where max torque is produced, the fuel curve needs to be shifted accordingly. This means the stock fueling curve is likely to be on the rich side in the mid rpms (hence the negative numbers suggested for some pipes at 6700 HI), and too lean at higher rpms, which can be adjusted for using the control box.
An important factor to be aware of is how the stock fueling behaves when the exhaust valves open. To meet emissions and to allow good fuel efficiency, the engine is programmed to run lean before the ex. valves open. Then, to produce more power safely, the engine runs rich just after the valves open. To complicate matters worse, the valve opening is delayed at higher elevations (around 8500ft and above), which can suddenly cause the engine to run too lean if you are already removing fuel in the mid-range. Some people just run richer at lower elevations so their tuning is safe for higher elevations. Another solution is to use the map feature and to load different maps depending on the elevation.
I think the best solution for this issue is to use a method I devised to bring the ex. valve position signal into the control box using the TPS input, then using the Nitrous activation features, create an RPM window where fuel (N2O fuel) is added when engine is above a fixed rpm (5500rpm) and stays on as rpms increase until the exhaust valve opens, which causes the TPS signal to drop and shuts off this extra fuel in order to cover this lean spot. This way, you don’t have to guess the rpms when the ex. valve opens and tuning is much more consistent. (this is a little difficult to understand at first, somewhere I think there are instructions that explain this).
One other issue to be aware of is on the 05 and the 06 M7’s (esp. at higher elevations) there is sometimes a lean bog that develops around 5000 rpms (just as throttle is opening after clutch engagement). Some people have changed clutching to get around this, but it can simply be fixed by adding 2-3 numbers at the 5000 LO and MD settings.
In general, the 05 Arctic Cat factory programming is on the rich side (fuel can be safely removed on a stock sled), the 06 is a little leaner (mostly on the top end), and the 07/08 programming is generally leaner due to emissions requirements so sometimes performance can be gained by adding fuel on a stock sled.. Using EGTs and an Air/Fuel gauge can greatly help in getting tuning spot-on. I highly recommend using the nitrous button which can be configured to capture/freeze the Stats screen during riding –push it when you encounter a rough spot you’re trying to tune in order to later stop and see exact rpms and engine load conditions. There is also an LED that can be plugged into the Nitrous harness – the box can program the LED to turn whenever engine load is in MD, or during ACEL, or during Nitrous activation.
