Mac,
You'll only be racing with people in the same class as yourself, i.e. age and engine.
MiniMax (11-16 yrs) is the lowest powered class of the Rotax family, and uses a very restricted 125cc 2-stroke TAG engine. All Rotax engines are sealed and have a log-book showing the service history.
By taking the restrictor out of a MiniMax it is converted to a Junior Max (age 13-16 yrs). It is one of the most powerful junior classes, with top speed about 70 mph.
I've copied this info from the
www.abkc.org.uk website which has more info about starting karting. Some of the pages over there don't display properly, which is why I copied the relevant info.
Dan