As I recall, the valve springs are really weak on these heads and should be replaced before seeing any decent rpm (eg., 6000). That info comes from Super Ford from about 7 years back. Since then, I don't know if World Products started using better valve springs. Maybe someone else can chime in (?).
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Russ L
'91 LX
Procharger, 3 row intercooler, extrude honed Cobra intake, Mac full Length Headers, 30# inj., 73mm C&L, 75mm tb, E303 cam, 289 rods, ported E7 heads, MSD, T-Rex w/255 lph Walbro, 5 lug conversion, Cobra R wheels, 3.27 gears and Moser Axles.
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