i think its the differance between exhaust stroke and intake stroke,you dont want the valves set for one when they should be doing the other.or some thing along those lines


oh what a feeling:
#1 86 xtra cab 22R,EB 261 cam ,Hooker header,2" ex with cherry bomb, Aussie powered
#2 86 sr5 4x4 efi parts truck
#3 87 2wd parts truck
84 supra yard art