I was worried this might happen. As you can see from the pictures, only two of the speaker's mounting holes line up with the adapter. I've tried every position possible and even considered drilling additional holes, but the diameter of the adapter's hole is just too big to even add one more screw on the bottom half.

My question is if the speakers should be fine without having screws on the bottom half? Will the door panel hold the speaker in place to prevent it from "flapping" against the adapter?

Thanks!

If your speaker isn't properly secured, it will work, but it will rattle like a lot and sound just awful. That's one of the problem with those cheap speaker adapters, fitment usually leave a lot to be desired. If you want a nice permanent solution, I make custom speaker adapters for most Nissans with 6.5" speakers, but I have yet to make an S13 adapter. Here's the ones I made for my car:




They are made of PVC so they won't warp or crack. I've considered making sets for S13s, but I wasn't sure if there is much of a market left for them. Shoot me a PM if you're interested in having a set made. Good luck!