The camshaft is the biggest killer of power in the 3.9, 5.2, and 5.9 Magnum engines. (Click here for more information)
The number 2 power killer is the intake manifold. The OEM intakes and cams are designed for unloaded trucks and that drive in stop & go city traffic or on the highway with no load – go figure!
Anyway, the most bang for the buck change is to upgrade your camshaft (HUG SER9703ALN-14V6 for the 3.9, HUG SER9703ALN-14 for the 5.2, HUG SER0814ALN-14 for the 5.9) with the proper valve spring and retainer kit (HUG1197 for V6, HUG 1199 for V8).
Owners of 5.2 V8s have seen chassis dyno increases of 23 hp and 35 lb/ft torque at only 2000 rpm and maximum gains at peak of 25 hp and 40 lb/ft torque. Owners of 5.9 Magnums have seen 31 hp increase at 4700 and a whopping 48 lb/ft torque at 3500 rpm – they have trouble keeping their foot out of it. Even if you are pulling a load, you should notice an increase in mileage. No other modifications will make this much change for this little money.
Our Fi Airgap (HUG 5409) intake manifold will eliminate the troublesome plenum gasket failure as there is no gasket to fail. The Fi Airgap will allow more airflow above 3000 rpm which allows the cam to do its job better above 3000rpm. The injector angle is changed and the airgap intake runs 30° cooler than the OEM keg style intake, these changes help improve both power and mileage. The Fi Airgap and a tuner will show about a 50 hp + 60 tq improvement.