SLP 40-66 primary spring which is 120-300lb rating, a polaris gold or black secondary spring (they are the same spring w/ same lb ratings, just different part numbers & color is all). And IF YOU CAN find one...and that is a big IF...Try to find a EPI Helix with the part number QA-2. It is a Quad Angle helix that does wonders on that sled, also I switched to slippery buttons because of longevity but I also used it with stock regular old cheap buttons and it worked fine. Don't bother with switching out weights, there isn't any advantage to that. That sled works best with the stock M5 weights. Call EPI to see if they have any left on the shelves, sometimes they find one laying around. I've been checking eBay for awhile now to find another one but no such luck there so EPI is your best bet. Also one thing I will say is I am not a fan of EPI's suggestion for the primary spring on the sled, I tried it but bleh, the 120-300 works better imho. They make a clutch kit for it with helix and their 2 springs suggestions but at 165 dollars you can do it cheaper and with better springs imho. I love EPI products but not for that engine and clutch combination.