It adds 4 degrees of timing to the whole curve. Does not really change the curve, just advances the existing one. Gives the bike more low end grunt. If you are running high compression you will have to use higher octane fuel with it. But your bike will feel like it's fuel injected on the low end, real snappy, and you won't feel any difference on the top end. Neat little $20 trick. Woke my Raptor up big time.