Pull your ECU out... The ECU has a specific amount of wires from each side, lets say, the S14 ECU, upright, has 8/10/10/10 or 8/7/8/10, of course, thats dual layers... Sounds complicated? Well how about this. Look on your ECU, and count the number of wires coming out of each side, in each column, divided by a thick plastic (noticeable). Ok, now we got that, lets look at the chart of the engine years by ECU.
Chassis Year Engine Slots
S15 1999+ SR20DET 8/7/8/10
S14 1996-1998 SR20DET 8/7/8/10
S14 1993-1996 SR20DET 8/10/10/10
S14 1993-1998 SR20DE 8/7/8/10
RPS13 1996-1998 SR20DET 8/7/8/9
RPS13 1996-1998 SR20DE 8/7/8/9
RPS13 1991-1995 SR20DET 8/7/8/9
Ok, now you got the slots determined on your ECU, you can use this slot code to partially determine your engine model. Now its time to use the color code of your motor.
Chassis Year Engine Color
S15 1999+ SR20DET Black
S14 1996-1998 SR20DET Black
S14 1993-1996 SR20DET Black
S14 1993-1998 SR20DE Black
RPS13 1996-1998 SR20DET Black
RPS13 1996-1998 SR20DE Black
RPS13 1991-1995 SR20DET Red
Of course these are not the only determining factors, due to that some engines are equipped with VVTI, which are the newer motors, they will have the slant rear along with the frontal hump.
Chassis Year Engine Rear Slant
S15 1999+ SR20DET Yes
S14 1996-1998 SR20DET Yes
S14 1993-1996 SR20DET Yes/No
S14 1993-1998 SR20DE Yes
RPS13 1996-1998 SR20DET No
RPS13 1996-1998 SR20DE No
RPS13 1991-1995 SR20DET No
Chassis Year Engine Front Hump
S15 1999+ SR20DET Yes
S14 1996-1998 SR20DET Yes
S14 1993-1996 SR20DET Yes
S14 1993-1998 SR20DE Yes
RPS13 1996-1998 SR20DET No
RPS13 1996-1998 SR20DE No
RPS13 1991-1995 SR20DET No
Chassis Year Engine Gear
S15 1999+ SR20DET 6
S14 1996-1998 SR20DET 5
S14 1993-1996 SR20DET 5
S14 1993-1998 SR20DE 5
RPS13 1996-1998 SR20DET 5
RPS13 1996-1998 SR20DE 5
RPS13 1991-1995 SR20DET 5