Some ways to improve the performance of a diesel engine include adding a high flow exhaust system, changing or upgrading the computer chips in the Electronic Control Module, upgrading fuel injectors, upgrading air intake systems and changing differential gear ratio. Each of these changes alone improves diesel engine performance.
Aftermarket exhaust systems all cause the engine to expel exhaust gases more efficiently and faster than with the factory system. Diesel engine ECM's, especially in diesel trucks, are set to keep engines below maximum power output to meet fuel efficiency and emissions standards. Aftermarket chips and programmers allow the engine to unlock more power. Changing differential gear ratio to a numerically higher ratio can help deliver more torque and give more power, especially with larger tires or while towing.