What about larger exhaust pipe? If you change from the stock 1.5" pipe to 1.75" pipe will it make more power? NO, the pipe won't make any horsepower. But if your engine needs to breathe, the pipe size can be holding it back

Consider that 1.5" pipe made 83 bhp with the Datsun A12 GX twin-carb engine. If you go up to 1.75" pipe, it will be sufficient for an engine making 108 bhp (engine dyno hp)

So yes, for a mildly-worked A12, 1.75" pipe is overkill. But for a more aggressively worked engine, 1.75 is a worthy upgrade. What about 2" pipe? If your A12 makes more that 108 hp, get back to us with your advice on how you achieved that on a budget!