Differences in CRX's:
88-89 CRX's don't have side impact beams in the doors, the 90-91 do.
All CRX's have rear drum brakes except the 90-91 Si's
90-91 have a round instrument gauge cover while the 88-89 one is more squarish
88-89 door moldings are taller and flatter, the 90-91 ones are shorter but stick out further and have a beveled edge to them.
90-91 rear lights have a 1/2 inch black edge all the way around them, the 88-89 do not.
90-91 have have fake air ducts molded into the bumper
88-89 have slightly different front and rear bumpers than the 90-91
90-91 bumper mounted turn signals are clear with amber inserts in them, the 88-89 lenses are just solid amber and shorter in length.
88-89 Corner mounted parking lights have their mounting screws visible while the 90-91 ones are attached by hiden screws.
91 and perhaps 90 headlights have a vent in them to help prevent moisture buildup.
90-91's are the heaviest, the 89 is lighter, and the 88 is the lightest. In each year the hf is the lighter model, then the DX and finally the Si weighs in at the most.
88 manual transmissions have an input shaft with 21 slpines
88 has a 21 spline input shaft, the 89-91's have a 20 spline shaft
90-91 clutch is 212mm, the 89 is 200mm and the 88 has either a 200 or 190mm, I can't remember which.
88 does not have a clutch safety switch. Which means it will start without having to press the clutch in.
88 Si models have 105hp, the 89-91's have 108hp due to different ecu settings and possibly a slightly different cam.
88's have pillar mounted seatbelts,90-91 have door mounted belts, 89 si's and dx's have door mounted belts, 89 hf's have pillar mounted belts.
Models with door mounted belts have a wider pillar at the end of the door to accomodate the belt mount, this also means that the glass is and inch or so shorter.
90-91's have a red seatbelt warning light built into the dome light.
Rear lower control arms changed between the 88 and 91 years and the rear shocks have different mounting points but I'm not sure what year the change took place.
88 has slightly different sized front shocks.
88 ecu has a different internal design than the 89-91 but the inputs and outputs are the same and ecu's can be swapped between years.
88-89's have the hazard light switch on the top of the steering column, 90-91's have it mounted on the dash.
88-89 Si seats have a white pinstrip, 90-91 Si seats have a red pinstrip.
88 has a pocket at the bottom of the drivers door
90-91 Si's and perhaps the 89 Si have a mesh pocket on the back of the seats.
88 cam indexing is the same for all the engines, 89-91 si's have indexing that is different from the other engines.
90-91 and possibly the 89 have larger reverse lights that are set further to the sides than the 88