I saw somewhere that running an EFI car without a Cat will decrease the MPG

Is this true?

 

 

 

Gannon

different cars could likely see different results. for the ER27 (same motor as EA82 except 2 more cylinder) i saw no decrease in mileage without a cat, with a cat and with a high flow converter, i've had all different combinations. i saw a 2 - 3 mile per gallon increase in highway mileage when i replaced the stock muffler with a dynomax straight through muffler. i drive 30,000 - 40,000 miles per year highway miles. around town driving may not have the same results.