Camshaft advance +/-

[sext7366]

What is an acceptable amount of timing advance for a cam...I have heard that some run there cam 4 degrees off, but what are the repercussions to doing this, because I have narrowed it down to two cams but happened to notice that if the cam is run 0 degrees to -8 the power goes up until the -9 mark. running a neg 4 may not be dangerous but I would think a -8 could be. I know it helps low end to advance it and top end to retard it, but how much is too much...and will this affect the idle in a similar way more low end=better idle, and more top end=lopier idle?