The following listed classes, sometimes known as "Bore and Stroke Classes", are generally unrestricted. This means that for these "unrestricted" classes, there are only the restrictions detailed in the previous "General Technical Summary", piston displacement, hull requirements, driver age requirements, and any additional class restrictions listed below.

With the exception of World and National Championships and at record events, motors eligible for an unrestricted class may participate in races scheduled for a larger unrestricted class. This is called a "step-up". The "step-up" must register as a "step-up" on the entry form. The "step-up" will receive points for the race only if there are enough bona fide boats of the scheduled class in order to qualify for points.

Motors legal for APBA's Stock and Mod Categories are also legal in the PRO Category's unrestricted classes. When these motors are run in their comparable PRO class based upon their piston displacement, they are referred to as "cross-overs" meaning that they have crossed over from their comparable Stock or Mod class.

At non-championship and non-record events, certain older motors, which utilize deflector scavenging, are allowed to run in a smaller class than their displacement. These motors are called "deflector step-downs".

The following table shows many motors utilized in the Stock and Mod categories and the unrestricted PRO classes where they are allowed to run as a "Cross-over" and/or as a "Deflector Step-down".