almost everything affects a blowers boost output. the more efficient your heads are or if you have certain cams or longtube headers, etc. that will all lower your boost output with the same pulley combo (its making your motor more efficient). then when you make it colder your iats drop and the efficiency of the blower goes up and makes more boost. it goes both ways. its weird. and roots and twin screw blowers have bypass valves so the blower isnt boosting at idle or when ur cruising.