They can only help due to making the motor more efficient. Especially if you have SCT and get get a new tune written for them. I get better gas mileage in my truck with all the mods I have done than I ever did before. I average about 17mpg on the highway and about 14mpg mixed. The best i ever got stock was 18mpg and that was only one tank going downhill from Flagstaff, AZ into New Mexico. I normally averaged about 15mpg stock on the highway and about 12-13 mixed.