Please read the stickys at the top of this forum Beginner’s Forum - Nissan 240SX Forums for mods to increase HP. Short list is intake/header/exhaust/s13 cams/timing advance without getting serious.
Bigger injectors and o2 sensors will NOT give you any HP what so ever. a bad front o2 affects hp, and MPGs, and overall engine operation. a new one will restore some hp lost, but you wont gain above stock.
OEM injectors are good to ~210-220whp IIRC. No need to upgrade unless you are turbo.
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