The 6.4 is a stroked 6.1,the 5.7 could be stroked but the bore is alot smaller so it wouldn't make it to 6.4. The info I've seen on the 6.4 have the MSRP at $15,900,I'm sure the price will come down, and be more competitive with GM's LS7 which is $12,900.The HP rating advertised at 505hp,I've seen dyno #'s above 560hp