6.4 hp
This interesting post was at challengertalk.com. Dealer claims the 6.4 is rated at 475 hp.
"My fiance and I took a walk around a sale event here in Southern Oregon and I had a chat with one of the sales/marketing guys from Lithia Chrysler Jeep Dodge in Medford.
He told me that they had started receiving info on the 2011's, and specifically I asked about the 6.4L HP rating. He told me that initial tests on test cars and power plants have indicated that the 6.4L is going to be rated at 475 HP and 470TQ. However, he also said something interesting in that he said this is based on the engine running at 65% capacity of power, that it has been tuned down to get maximum engine life (and warranty claims) down.
According to him and a Chrysler rep that was there from Auburn Hills, the first 6.4L SRT8's tested in April weren't detuned (and running at 90% capacity), and were putting out 505 HP. Chrysler's warranty and legal stepped in and determined that they could reduce potential claims by 30% if they tuned it down to 450. A compromise was met at 475.
He did say the SRT10 was briefly reconsidered two months ago, but it was not in true testing. He did not say anything confirmed about the 5.7L being underrated, but he just kind of smiled when I mentioned I put down 332 RWHP on the dyno on a stock motor and that something wasn't right. He did mention that "The 5.7L is a very surprising motor isn't it? We have that poor motor so tamed down".
Interior materials and color scheme is changing, specifically in gauge design, but the overall interior isn't changing. He did mention at least as it stands now most of the 2011 parts are interchangeable with 2009/10's."