My 385 hp 408 pushes the dak to 12.2s at around 109. The motor runs great til about 5700 rpms then it loses power and starts to pop(I'm told that you can't hear the pop from outside the truck.) it has a 750 holly. At first I thought it was a fuel supply problem but I put a gauge on it and it never drops below 5 lbs. I emailed blue print engines and they said "don't rev it that far" but it seems to me there is something wrong making it do this and is probably slowing the truck. It had a dyna mod hei that I replaced with an msd 6 al and the problem continues. Oh this is a second had motor and the guy I bought it from said when it was new it pulled to 6000 rpms even tho it was faster when shifted at 5600. I'm thinking carb or valve springs and ideas? Ps it ran 12.40 when it was in his 71 dart.