I don’t think there’s a valvetrain problem at 5400........ but I think it’s getting unhappy at about 6k.
So, no....... if that’s happening, it’s not affecting the peak output at 5400.
The motor in the Duster, which should be more air flow restricted with the stock intake, air filter, and exhaust manifolds, along with heads that don’t quite flow 255cfm..... makes peak power at 5700........ has only lost 12hp at 6600.
This motor loses about 50hp from 6000 to 6400.
