The 4-speed '88-'91 Civic is the STD model. Should be a D15B1 engine instead of the DX D15B2. Different camshaft and ECU, and slight TBI difference. I've seen them with a close-coupled catalytic converter, but I've heard that all years might not have it. It has about 20 HP less than a DX.
First through fourth gears are the same as the CRX HF, but it has the DX final drive. So it'll rev slightly higher than a DX in top gear, but there will be slightly less friction with only four gears in the transmission.
STD:
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DX:
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