As you may have guessed, the "12 Valve" refers to the number of valves the head has. Later (mid-year 1998) these engines received numerous updates and the new slang for these engines was "24 Valve". Yes, again that is because there were four valves per cylinder for a total of 24.
The 12 valve Cummins originally hit the light duty truck market 1989 with 160 horsepower and 400 ft lbs of torque. The engine used a Bosch VE rotary injection pump to feed the pop off injectors. Four years later (in 1994) the second generation of the 12 valve was introduced. This engine was rated at 160 horsepower and 400 ft lbs of torque for an automatic and 175 horsepower and 425 ft lbs of torque for a manual. These engines saw a new inline piston driven pump. The new piston driven pump (commonly called a p-pump) was still a Bosch pump model P7100. This p-pump has become one of the most popular injection pumps to be modified in the aftermarket. It was too long before people realized that by simply adjusting a screw and moving a plate, they could "turn up the pump" and increase the power of their engines.
By 1998, just before the 12 valve engines were replaced with the 24 valves, the factory was rating the automatic at 180 horsepower and 420 ft lbs of torque. While the manual transmission trucks were rated at 215 horsepower and 440 ft lbs of torque. But as we have seen over the years, this was not even a scratch on the surface to what these engines could do.
So, when we started to write this article, it wasn't hard to find some of the biggest and baddest names in the 12 valve marketplace. We were a little surprised that even though this engine hasn't been produced in over 10 years, it still remains a very popular engine to modify.