A dyno is a tuning tool, not a penis yardstick. Comparisons on a different dyno, different day / weather is meaningless. Moreover, chassis dynos can be fudged to read whatever you want them to. It's a very common practice for speed shops to have a "happy" dyno to make their work look better. ET and trap speeds will tell you what's actually happening in the real world. For an unmodified SS, 225 at the wheels probably isn't too far from the truth when you factor in drivetrain losses.