My ET calculator says with your 550 hp in a 2400 lb car you should turn a 10.3 traction and launch permitting. I ran the 1/4 with the 355 that produced 386 hp. I haven't run the G-Tech yet on the new 427 but the calculator and G-Tech have always been very close. The calculator says a 9.7 with the 526 hp 427.