These MHS / PAC RPM Series Valve Springs are designed for use with 4.6L / 5.4L 4V B, C, 03/04 Cobra / Mach 1 and Navigator Cylinder Heads. They are supplied with your choice of 4130 Chrome Moly or 6AL-4V Titanium Retainers with a +.050" Design to raise the Installed Height from the typical 1.430" to 1.480". These Valve Springs are manufactured for us by PAC Racing Springs right here in the USA. Suggested for all 4V applications running aftermarket camshafts up to .500" lift and up to 25lbs of Boost.
There really is no need to go any higher than .480" Lift on Non GT500 Style 4V Cylinder Heads. Although these springs are more than capable of handling .500" Lift at a 1.480" Install Height, there really is no reason for it and .480" lift is our suggestion for these springs.
We also encourage everyone running aftermarket 4V cams and valve springs to upgrade to the Accufab Secondary Timing Chains as the OEM Secondary chains were just not designed for much more spring pressure than stock.
