Subaru sti running on e85, how to convert it back to premium?

Look through the Access Port and see if there is a map for premium gas. There has to be. No tuner in their right mind would just tune for E85 with the limited availability anywhere. All you have to do is reflash to the Pump gas map and you should be fine. If the car is from somewhere else and it's tuned for 92 or 93, you will be fine to drive it as long as you stay out of boost Then you will have to have the car re tuned for whatever octane you use where you live. As far as using the E85, that's up to you. For a slight sacrifice in mileage, it's a lot cheaper and rated at well over 100 octane so you can run much more boost and aggressive timing. In colder areas though, because of cold start issues, some gas stations change the mixture to contain more gasoline and that is dangerous if you are tuned for a specific mixture so make sure the station you use does not do hat if you decide to run it in the winter. Also switching from gas to E85 is simple. Run the tank low, fill with premium and switch to a gas map with the access port. Switching back to E85 is ta little trickier. You have to know exactly what the tuner did when it was tuned for E85. If you don't get the mixture right and have to much gas mixed with the E85, you an run into detontion prblems. I think your best bet is to find an Access port tuner in your area and talk to him. Cobb is very picky about who they sell their tuning software to so if a shop tunes with the AP, they are pretty reputable. That way you can have all your questions answered and be enjoying your car sooner.