Chizzle: Are you sure about the 390HP in a 5.7L. All the documentation I see is 375HP 410 Tq for the 6 speed which I have.The newer (2010-up) 5.7s are rated at 390, and you are correct most 2009-up 5.7s put down a baseline of around 335hp on a dynojet.
Keep this in mind: dyno testing is more about measuring the effect of changes made rather than putting down the largest number, a dynocom, mustang, or dynojet will all put out different numbers for the same setup.
Now the RAM trucks show the 5.7L as 390HP. Is that where you got that number. Appreciate if you can lead me to an article or link that describes the Challenger 5.7L with 390HP. The motors for the RAM truck and the Challenger are supposedly different.
As we have wrote about the Dyno data leaves me to believe it is under ratted and close to 390. But all the brochures and data say 375HP. Hope you can show me something because that would be cool.