Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---


Understanding AFR

Forum Posts



Tech Articles

Discussion and questions related to the course Understanding AFR

= Resolved threads


Can you tell me about Altitude with regard to AFR Compensation? My goal is to optimize an OE NA engine’s ability to traverse the 6500ft (1980 meter) elevation change I encounter while traveling. The annual extreme ambient temperature range is -30 to 120F (-35 to 49C).

Thank you

I think you will want to run the same AFR targets regardless of altitude. Your ECU does need to be tuned with barometric compensation to account for the altitude. Baro Compensation is very easy. Just think "half-the air, half the fuel", so 50kPa = 50% fuel, and 100 kPa = 100% fuel.

If your car is normally aspirated, and you are tuning at lower altitudes, try full dyno pulls, and 70 -90% throttle as those will be typical of a full-throttle blast up a hill at higher elevations. Also you make sure your fuel map is "following the trend" for lower MAP values than you currently see cruising, as that is what the engine will see at higher elevations.

You 'should' be able to run a baramic and an ambient temperature sender with your ECU.

If so, you can enter this correction for it, if it doesn't have an option to do it automatically - https://www.mide.com/air-pressure-at-altitude-calculator

For temperature, again if it isn't able to do it automatically, you should be able to find a suitable conversion chart on-line.

Your fuelling will be approximately proportional to the change in density, however it's varying.