Hello; Mike here. I am building a 2nd cylinder head for my Gen 1 which I plan to swap out this winter. I am going to put titanium retainers, and heavy duty valve springs on the head. I was looking at the APE springs, and retainers. I noticed the stock springs are a single spring and the APE look like a dual spring. Is there any performance difference from a single to a dual? Does anybody know what the springs are from Carpenter, or Cycle Concepts? Any help would be appreciated. thanks. Mike.