The CRX DX had a dpfi 90hp engine...it also had longer gears but still a 5 speed manual.

The CRX Si came with mpfi (about 15 more hp) but the powerband was much flatter compared to the DX so it make much more power for a longer time. The Si also had much shorter gearing making it accelerate very well (in addition to its smaller diameter wheels).

Also, 90-91 CRX Si's also came with rear discs (where all DX's had drums)

You can make a DX very quick...mine is built for H5 / ITC specs...it has a chipped ecu, competition head, retains DPFI and it has the Si gearing in the dx transmission (had to keep stock transmission case)...I also have rear drums but they do a good job as the car is not too heavy (about 2050lbs with me in it)