Can you port a sealed car subwoofer enclosure?

You can't exactly port a sealed box because its not designed for that purpose when it was built. A sealed box is for tight and accurate bass, not boomy deep bass! Your car subwoofer has to be recommend by your manufacturer, if its ok to place it in a ported box. If its recommended, its better to build your own custom subwoofer box and port it and do the maths correctly. Porting a car subwoofer enclosure is not just cutting a hole with a jigsaw and fitting a port in the hole, no it doesn't work like that. A port has to be correctly cut to the right length, in order to function properly and sound perfect.