ok i recently did a new build in my suburban with 4 OA 18's. the box is perfectly sized at 21^3ft i believe and the port is tuned at 32 hz. im having to problems here tho. the first is that because of my battery bank i have in front of the box, the box itself had to be scooted very close to the tailgate. as in the face of the box is like 2 inches from the tailgate at best. to counter this we "recessed" the port in on the face of the box in a flare of sorts so its more or less 8-10" off the tailgate giving it some breathing room. now the port itself is 703^3in. to me this almost seems to small for the 4 18s but when i have it playing you can stick your hand in the box and hardly if at all feel a breeze but pull it out and into the port and its a hurricane which leads me to believe we have perfect airflow in the box itself. yet i still feel like its being "cut off" and not unleashed to full potential. i should be able to do some nasty hair tricks with 4 18s rights? i mean i can do one now but id hardly call it a hair trick. granted the whole systems running off of a single brz 2400 right now (saving for a DD M4a) i still feel like it should do more. perhaps my expectations are to high but ill leave that for better minds to decipher.
for what its worth, i took the truck to a competition and put it on the meter with a mojo 4k at 1 ohm (12v system). at the time, my back liftgate window was busted out and covered with plastic and duct tape instead. it still did a 145 at 38hz. idk if that helps or not but my mind is racing here.
Big thanks in advance guys!