A vafc will only improve the vehicle if the factory ecu's tune is preventing the vehicle from making all the power that it can.
A vafc will only make an improvment if it is used to tune the vehicle using a dyno and wideband oxygen sensor.
The difference between the vafc I and vafc II is simply features, check out apexi-usa.com
There are much better solutions for an s2000 such as aem ems or hondata's 2006 s2000 ecu reflash.
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