hello everyone i got a 97 civic lx 4 door iv now modified too a SI with 4 doors. i was still recieving 550 km too a tank of gas. i just put on a single exit magnaflow exhaust 2.25inch with a 4inch outlet. now my gas has gone too maybe 350-400km a full tank... its now winter since i installed it a week ago, went from +2 too -10 i dont know if thats affecting my car? any suggestions guys i can have more information with questions.

 

In my experience the winter/cold weather months I always get at least 2-4 MPG (miles per gallon) less, I believe it's not only due to warming the car up for allot longer but I've heard gas companies use a lesser expensive "winter" blend fuel which I think is just cheaper overall and doesn't competely burn as effeciently so you get even worse mileage per tank.
Anyone else have theories or want to sort of confirm my observations?

 

okay so believing its cold and the exhaust together iv lost 6-8 mpg?