THD 89-93 Fuel Pin and Governor Spring

The Hungry Diesel fuel pin!

Made from 4140 and max hardened. This pin is properly cut, so to give maximum fueling, but not cut too deep to allow slide pin to slip past the O ring. The pin is also cut with a "flat" ramp design, as opposed to the common "progressive" ramps. This gives a much smoother fueling transition and avoids unwanted smoke.

3200 rpm governor spring is a great option and will give your truck a big boost in useable rpm power. 
3600 rpm is similar with more throttle response, more touchy feel to the throttle, but it’s not going to expand your power band much since it will be de-fueling and beyond air efficiency beyond 3000 rpm anyway. Your cummins wants you to shift and keep it in its max torque range. 60lb valve springs are recommended. 
4200 are very touchy with max throttle response and is there for a max performance application with supporting mods and goals.