Hey guys, I'm noticing recently that my gas mileage is slowly going down the drain w/ my vortech 3.12 pulley setup. Before I would average 270 miles per gallon. Yesterday I filled up at 211 miles when the light came on (about 13.5 mpg). I'm fairly certain I haven't changed my driving habits. AFR's look relatively normal compared to before. I cleaned the air filter my last oil change around 1k miles ago. What are some possible reasons why my mileage could be like this? I know I recently retightened my belt..... could overtightening it have caused this? What else could cause a drop in mileage?

 

Tighter belt=more parasitic loss maybe? I dunno, not a supercharger guy.

Have you checked your plugs?

 

Replaced my plugs about 6-7k miles ago w/ one step colder. Oh yea, forgot to mention i've had the SC for about 10k miles.