Quote Originally Posted by frdyam400 View Post
how would a colder thermostat effect your mpgs that is doing nothing to your engine to make it put more fuel in the engine, its not going to effect your computer to set the fuel higher
When your computer sees that the coolant temp is cooler than normal it richens up the AFR (air fuel mixer). Just like it does on a cold start up...a colder engine needs more fuel. Thus giving you sh!tty mileage.

And I would have at least some headers before you think about dropping pulleys. A smaller pulley is going to suck a lot more air into your engine and you need a way to get it out as fast as it's going in.