Using a single 8" free air is likely going to be disappointing to just about everyone. Free air works very well, but you need plenty of displacement to get the output that most people feel is adequate. Even though the opening may only be sized for an 8", you can run a 10" or 12" to give you some more output. You do not need the opening to be as large as the cone.

 

Just looking to have some low frequencies filled in. Not really spl. I had a 12" in the trunk before but the amount of space it took up was too much.

 

Gijoe is right, slap a piece of ply over the hole and mount as large a sub as will fit up to double the area. You want a sub with higher qts say .7 and lower Fs like closer to 20hz though a 10 or 12 will be higher say 30. Power is typically half a boxed rating so a 300w sub is generally good for 150w IB. You can model the sub to see the FR it will make, use sealed and the volume of your trunk. For example cheap pyle subs often have high qts and low fs and work well IB within the power they can handle. If you have a factory amp pay attention to the ohms of the driver they use. Output will usually be less than a box but the FR will dig lower. You can use a SS filter to raise power input but of course you lose bottom to whatever your SS is at, but you can come close to sealed outputs that way. It will run out of xmax at its limits that is why you need a SS or to limit power....depending on how capable the sub is. You put a monster xmax sub in there even if it tunes badly and you need to EQ it, it will have much more output than a small xmax sub.

 

SS filter to raise power input. I have been seeing this a lot what is this. I am looking at putting a 10" image dynamics ID10 in to the 8" stock hole in my Charger. I know I need a line converter to use the factory Wiring to connect to the amp. but what is this SS Filter. I was thinking about going with the 8 but everyone so far is against that because of the size just wont get there.

 

Or what about this

PIONEER TS-SW2502S4 10-Inch or
https://www.amazon.com/dp/B0054REBYK/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=2SY4DLLU99WDN&coliid=I3FPJQLWV83RPF

ID10D2 V.4 - Image Dynamics 10" 300W RMS 600W Max Dual 2-Ohm V.4 Subwoofer
https://www.amazon.com/dp/B00LI8BWWI/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=2SY4DLLU99WDN&coliid=IETQGA88YVOZP

Pioneer GM-D8601 Class D Mono Amplifier
https://www.amazon.com/dp/B00CFX58YI/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=2SY4DLLU99WDN&coliid=I2DJOWJUY8BGMS

Any feedback is welome

 

I have a sonata, what year is yours? I tried the 8 thing in the deck, and its not very good at all. If its a 2011 up to i think 2014 i have a JL stealthbox that is a pefect spacesaver enclosure for the car for cheap if youre interested. The 8" will disappoint you.

 

Mine is a 08 charger RT but I am going to cut it out to fit one of the 10's above. But now I found out I can not get just a LOC converter I Need a CAN BUS adapter so my subs will go over Volume 22

 

Sorry, my post was meant for the OP

 

My local shop, for awhile, was in reverse about using RE audios entry level 8. They were surprised by the actual output. Granted it wasn't SPL levels.