I've done it with 87 octane. The car runs ok on regular unleaded. Don't jump on the throttle. If you really calculate it you do loose 1-2 mile per gallon over premium. You do the math. Check your gas milage with premium & midgrade. I settle for midgrade with premium ever few fill ups. I put my car through mid to heavy accelleration .

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T