The only thing that I can think of is to simplify your explosion and don't use a lot of entities. Around April or so, I ran an experiment. I had over 600 entities shown on the screen at once which had a tiny skin size and only 4 polies. The frame rate was 18 fps. The best thing to do is just cut down on the number of entities. For something like your explosion, you could do that in just one entity, although it might be rather difficult.

My worst-case scenario. Think 38 ms is bad for the screen refresh time? Try 171 ms. This is with level geometry (blocks) only in my old project that I've almost abandoned. 171 is crazy! I can kick that up even higher too and it's easy to do.

Edit: come to think of it, I should check to see if the high entity count/low frame rate issue is due to a massive screen refresh time. I'll run that experiment again using the small skin, low-poly object.