ADR to main jet

I find Air Density Ratio % (ADR) confusing to me because I tune with Density Altitude (DA) I find it a lot easier to change the Main Jet one size for every hundred feet change in DA. Actually ADR has the same air density information but the way it is expressed is a little different. ADR assumes that your tuneup has the correct Air Fuel Ratio (AFR) in the motor and then expresses the changes in DA in a percentage of fuel change to keep that tuneup/AFR the same. So if the tuneup/AFR is right on at 1000 ft DA and it changes to 1200 FT DA then it tells you what percentage to change that fuel to make the tuneup/AFR correct at 1200 ft. I find it easier that if I am using a 80 main jet at 1000 ft and it goes up to 1200 ft then that is a 200 ft change so I now change the main jet to a 82. To use ADR then you are going to have to have a conversion chart or a calculator with you. ADR CANNOT be directly related to a main jet size without first converting it.

To convert ADR to DA the formula is DA = (-358.69*ADR)+35805
To convert DA to ADR the formula is ADR = (35805 - DA)/358.69


Hope I haven't confused you.

 

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