http://www.enginelabs.com/engine-tech/fuel-systems/explaining-the-effects-of-weather-on-mechanical-fuel-injection/?emailpopup=1

Atmosphere and how it affects your engine tuning

Increase Horsepower and torque.

Custom tuned chips improve performance, gas milage, torque, and horsepower while improving throttle response, towing power and eliminating the factory REV and Speed Limiters holding you car or truck back,

Knowing the mechanics of your racing engine is the most important factor but knowing what’s going on in the atmosphere and how it affects your engine tuning is necessary to improve power and consistency.

atmosphere, sea level, moisture level, octane level in gas all have a major effect on how your engine runs not only at different tracks but every run.

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