Most car's experience a slight drop in performance when the a/c is engaged. It's not unusual. With the a/c on the motor is driving an extra accessory, the a/c compressor. The more things the engine has to drive, the less power it has left to send to the wheels.
The power loss in smaller cubic inch engines is *generally* more noticable. SVT's have a relatively small V-6 (153 cid).
