I have a 78 with an L82 in it i run 94 oct in it however the engine pings on low rpm accelleration in the 1500 to 2000 range I have exhausted all the usual causes my carb is an elderbrock 650 performer my distributor is a mallory hei with adjustable vaccume advance both are brand new I can almost ellimanate the ping with the vaccume advance but it is still slightly there ,the curve springs are my next option has anyone had success with this if so what color springs did you use