1997 Subaru legacy rs, increasing efficiency?

Change all your fluids to lighter ones help(if you dont live in a hot area with high temps). This will help get some efficiency out of it, also get a more efficient air-filter, K&N or similar. They are expensive at first, but can be cleaned and used over and over. Change your plugs, but DO NOT use anything other than OEM replacements, which should be NGK Plugs. Subarus do not like Bosch, or any other plugs for that matter. Changing your fuel filters and cleaning your injectors should help as well. Also make sure your tires are properly inflated. And pull anything thats heavy and you dont use out of your car!

These are all pretty general tips for increasing efficiency that can be used on any car really. Subys can just be picky about some things.

Performance mods generally cost you MPG. The #1 thing you can do to increase efficiency is lift your right foot. If you press less on the gas pedel, you will use less gas (shocking I know). You could also reflash to lower your boost, but this is just using the computer ECU to do the same thing you could do with your foot. Tape a block of wood to the bottom of your gas pedel if you have trouble controling yourself.

Also, lighten your car as much as possible (remove the junk from the trunk), inflate your tires properly, and get a tuneup.

good way to start is with a good performance exhaust and a better air filter like a K&N high performance air filter. also a better spark plug will help something like a bosch platinum which is a very nice spark plug.