IIRC, The stock computer only does so much, the Higher you go in boost,the more your figthing the OEM ecu, as its advancing you i belive to compensate for what it thinks is right for a NA. it doesnt know what your trying to do. Effectivly it doesnt do good things with your tune because its a chaning variable. Most go with Crane or MSD ignition to controll timing. Typical rule of thumb is 15psi on a s20g. some get away with more, some dont. If your wanting to go that high, a MS system might be a better fit for you.