l have a 2005 Subaru Legacy GT (turbo). The owners manual says that 91 or higher octane gas is recommended... but it doesnt say its required. l was wondering if l could use 87 octane (middle grade); would that hurt my engine/ turbo because of the increased engine ping?

You should never use lower octane gas. Use the one recommended even though it is a bit more expensive. Using lower octane gas will diminish the performance of your car and will cause your car to use up more gas which means more money. In the long run, it is cheaper to use the recommended octane.

.yes lower grade gas will hurt the engine,,, turbos are hard on the engine...if you dont want it trade it for a regular 4 cylinder

you can BUT ur car wont run the same. its a performance car so it would need the higher octane fuel....if it was my car l wouldn't.

The only difference between the octanes is its ability to resist ignition or detonation (whatever u want to call it). Your higher compression vehicles usually run 91, 93 or higher octane, & any supercharged/tubrocharged cars & trucks will require the same.

Your turbo is creating higher pressure in the combustion chamber than a non turbo engine. So by using a lower grade octane, u run the risk of having ur fuel mixture ignite too early in the combustion process which can damage ur engine internals (worst case).

It sucks, but it is just the way it is . stick with the premium.

The car will run on lower grade gas. Actually if u do not push the car too hard, it will run just fine. If u do give it too much gas on a hot day, the ECU will pull timing at the first sign of detonation to not damage the engine. You may have to take it back to the dealer to reset the ECU though. But look, what do u have to gain by using 89 instead of 91? $1 to $1.20 a fill up? if u do damage to the motor, the dealer may test the gas to make sure u r using the recommended grade & deny u any warranty. l just think it is worth the extra dollar a tank to keep the car happy.

Yes.
But if you take the turbocharger out of the car, then you can use regular. But you would also lose at least 50HP.

You could try it but it will effect your fuel economy. You could always use regular and put in an octane booster. Since it is a turbo use synthetic oil in the engine.