The single valve springs do not require a new seat or different seals where as the duals will.
A set of valve springs can be changed in a matter of 2 hours with the correct tools, and is the best insurance a car with upgraded cams can have.
The single springs have been tested higher but we suggest a max rev limit of 8500rpms.
If higher revs or prolonged periods of revving i.e. road race applications, we suggest going to our dual springs which is more stable at higher rpms and can be revved to 10500rpms.
The Single Spring kit includes: Single springs firstname.lastname@example.org with either Titanium or Chro-Molly Retainer.