Do you know what they are wired too? I'm assuming you have them down to 1 or 2 ohms. Just want to make sure they aren't wired to like 8 or 16 ohms.
Anyway, a ported enclosure gives you the ability to really change the frequency response that they'll reproduce.
Take a loot at this plot below;
Your current setup is probably very close to the purple line (sealed plot)
The green line is an example of a low-extending flat response (vented plot)
The yellow line is an example of a peaking response (vented plot)
You can see that you have a lot of control over the sound of a sub woofer when using a vented enclosure.
So to answer your question, yes, a ported enclosure can yield you a "louder" sound.