To maintain a high level of competition, the Sanctioning Body (IHBA) has classification system that organizes the boats into tightly matched categories. There are two basic categories: ET classes based on elapsed time and Pro classes based on structural differences. Drivers can choose either category and use this to their advantage.
Speed is not the determining factor in the ET classes – the only thing that counts is the time (seconds) needed to complete the quarter mile course. Drivers can clock slower times in their specific ET classes, but face disqualification if they go faster. There are no structural restrictions in the ET classes, which allow a wide variety of boats to compete. Driver skill and mechanical modifications producing acceleration are crucial in this category of classes.
The Pro classes depend on structure, including the variables: engine structure, fuel type and hull structure. Engine structure depends on physical size and method of introducing fuel. Engines can be normally aspirated by a carburetor or fuel injection system (Pro Gas) or supercharged (Blown). The supercharged engine uses a blower to force air into the engine, resulting in increased compression per cylinder. In the Pro classes, engines can not exceed 500 cubic inches and must burn a gasoline fuel. In Blown classes, engines can not exceed 565 cubic inches and can burn either methanol (alcohol), nitromethane (Top Fuel), or a combination of the two (Blown Fuel Jet).
The third variable in the Pro classification is the hull type, including hydroplanes, flat bottoms, or jets. By this definition, a gas burning boat with a carburetor or fuel injection system and a hydroplane hull is a Pro Gas Hydro (PGH). A methanol burning boat with a blower and a flat bottom hull is a Blown Alcohol Flat (BAH).
- Top Fuel Hydro (TFH)
- Top Alcohol Hydro (TAH)
- Top Fuel Jet (TFJ)
- Top Alcohol Flat (TAF)
- Pro Modified (PM) 7:00 Breakout
- Pro Comp Eliminator (PCE)
- Pro Gas Hydro (PGH)
- Pro Eliminator (PE) 8.00-8.99
- Top Eliminator (TE) 9.00-9.99
- Modified Elim (ME) 10.00-10.99
- Stock Eliminator (SE) 11.00-12.00
- River Racer I (RRI) 12.00-12.99
- River Racer II (RRII) 13.00 plus
- PWC I (Ages 10-14)
- PWC II (Ages 15 & Up)
Drivers usually choose a classification at the beginning of each season and stay with their choice for the racing year. A driver rarely changes classifications because of the point system. Points are based on performance, compiled over the length of the season. Changing classes would almost surely deny a driver the chance to take points honors in a particular class, for the season.