|Outboard racing under the auspices of the American Power Boat Association (APBA) falls under four different categories.
The Stock Outboard category is essentially spec racing. Engines must be left for the most part as they come from the manufacturer. The only changes allowed are in the interest of safety or to make the engines more suitable for racing. For example, the lower unit has only one gear – forward – and it’s always engaged. And the motors can use pump gas only. Minor technical changes to engines are permitted only after a thorough review by APBA’s Stock Outboard Racing Commission. There are also limits on boat dimensions and total racing weight as shown in this rule book. The idea is to make racing a contest of driving skill. Minimum age for drivers is 14 in A Stock Hydroplane and Runabout, 15 in 20SS Hydroplane, 18 in D Stock Hydroplane and Runabout, and 16 in all other classes.
Modified Outboards are similar to stock in that they use pump gas and there are some limitations to engine modifications, but not many. Mod racers spend a lot of time at the milling machine and use more exotic exhaust systems. They can also be very loud. Class specifications and age limits can be found here.
Professional Racing Outboard (PRO) refers not to the pay of drivers, but to the fact that the PRO category takes modified to a whole ‘nother level. Any methanol burning piston-based motor can be used within the cubic centimeter limits of the particular class (there are two exceptions, KPRO and OSY 400, which are considered entry-level classes to some extent and closely resemble A and C Stock Hydro respectively).
Outboard Performance Craft (OPC) has come a long way since its beginnings as the “Outboard Pleasure Craft” class. This category of racing features some of the biggest, most powerful outboard engines in Powerboat Racing. OPC engines can range from off-the-shelf production engines to heavily modified, high tech engines built for world record speed. Today’s most high tech OPC race boats can start from a dead engine start, go 0 to 100mph in 6 seconds and turn 180 degrees with forces of up to 5 G’s. These tunnel boats are the fastest turning vehicle in the world!