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11.2.4 High Altitudes Performance Decreased

Q: When I travel to high altitudes, my performace decreases.

This is likely due to the effect that high altitude has on air density.

At sea level, 100% throttle is equivalent to ~100 kPa map. As the altitude increases, the kPa at max throttle decreases (Colorado Springs is ~80kPa at 100% throttle). We suspect that Harley has invested some engineering time in somewhat automatically compensating for these barometric changes, but it is wise to inform your tuner beforehand that you may have major altitude changes in your travels. Large altitude changes tend to exacerbate any minor fuel issues, especially on vehicles with aftermarket performance parts. Depending on the Application Version, they may be able to preemptively alleviate the impact.

Some areas to pay attention to:

  • Don't ignore the low or high MAP idle positions. Travelling motorcycles may someday experience conditions that put it in these ranges.
  • If you are in a high altitude area, you may not see MAP much above 80. Anticipate the travelers needs by predicting and adjusting the values above your max MAP too.
  • The most important VE calibrations for this issue are the extremes: Low TPS & low RPM or high TPS & low RPM. Spend a little more time to get these areas just right. If the motorcycle is equipped with oxygen sensors, the closed loop system should alleviate most symptoms in the cruising range.
  • Read up on the impact that air density and temperature changes have on engine performance. Knowing how something works can often lead to developing your own excellent solutions.