The peak RPM on my 440 is steadily going lower and lower. When It was first built it would buzz to 6500 no prob. Now it it struggles to hit 5000. The combo is a .030 over 440 with a .509 cam, ported 906 heads,Eddy performer RPM with a 850DP. Ignition is a MP electronic distributor with a chrome box. timing is 37 degrees total. I use a Carter electric fuel pump that puts out 15 psi thats regulated to 7 psi. floats in the carb are dead on. I'm guessing valvesprings but what else could it be? Who makes the best valvesprings