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Mass Flow (AFM / MAF) vs Speed/Density (MAP)
The ECU can calculate the engine fuel requirements by two methods - mass flow (using the air flow meter) and speed/density (using the manifold pressure sensor). Each requires a different tuning method.
It it necessary to use a lambda meter (air/fuel gauge) to tune to fuel tables. Some engines utilize a wide-band oxygen sensor which is useful for tuning, otherwise most dynos are equipped with a lambda meter. It is best to tune so that the air/fuel plot is fairly flat.
For the Civic Si / Type R the internal oxygen sensor is of a semi-wideband type. While its range is good (10.7:1 - 20:1) we have found that it progressively reads richer as the exhaust gas temperatures increases. Therefore the wideband is useful for partial throttle and naturally aspirated engine tuning, but for forced induction we recommend the use of an after market wideband if you are tuning without a dyno.