Wat can I do to get better gas milage in my 1989 chevrolet Corvette without droping horsepower or torque?

You don`t say what if anything you did to increase horsepower.if you have done a mod to the motor then there probably is nothing you can do as more horsepower requires more fuel to be burnt to run properly.if not then you can try changing the thermostat as if its not working properly it can have an effect on gas mileage also a bad coolant temp sensor can have the same effect.you may have to change your driving habits,no jackrabbit starts from a stop and not braking till the last second.constant revving of the engine anything you do that causes you to push on the gas pedal will result in more fuel being used.even driving above 60mph(100kil) will cause more fuel to be used.what about tune-up has it been awhile.

Make sure the engine is properly tuned. Check tire inflation. Accelerate slowly. Anticipate stops. Probably not what you wanted to hear when your driving a Corvette but there are no magic solutions.