Info by Changez
For people wanting to upgrade from the standard single valve spring and also want increased seat pressure, CrowCams offer double valve springs for the E15ET engine.
The part number from CrowCams is 4220. The standard e15et shims are all this is needed and spring retainer cap will hold the double spring perfectly. The double springs have been tested and measured 20 pounds more seat pressure than the standard springs did.
For further information on these springs, Visit CrowCams’ website here.
Anyone that may know of other springs that can be used for such a modification please let me know.