Talk to a diesel mechanic in your area. One told me that for EPA regulations, and fuel consumption, the injectors are turned down (fuel pressure) about as low as they can go (lean fuel/air mixture) and still be safe for the engine. He said that the injectors can be turned up for quite a bit more power. Claims a 60 HP (factory rated) engine could be turned up to 80-85 HP at no expence in reliability, may be better for the engine because it's not running so lean. I would think you should be able to get 20-21 HP with no problems, based on that. I also know it is common for farmers in this area to turn up the injectors on larger tractors.