1999-2004 TRX 400EX Rev Box (BIG40-R01)The Big Gun Rev Box for the Honda TRX 400EX is a high performance electronic upgrade designed to unlock the full potential of your engine. As an affordable alternative to expensive OEM replacement CDI boxes, this unit is engineered to provide a more aggressive power delivery. By increasing the overall RPM limit and advancing the timing curve, the Big Gun Rev Box allows your engine to pull harder for longer, providing a noticeable boost in top end