Spin will generally lead to more MPH, plus air conditions can also account for the increased MPH as well. Never found a street butt dyno to be very accurate, or sound of the car to equate to more power, just sayin. Video is ALWAYS your best friend. Look for a track rental and get in on it, your lack of a legal cage wont matter then. Usually one or two track rentals at Famosa in the spring. Yep will cost you more to get in but you will be free to try some stuff t make it work..