the weakest link in the foxbody is the block. Depending on the year the pistons are different. 90-93 pistons are forged but the block will literally crack down the middle at around 500whp. some people push them to the limit and experience nothing others at 450hp have cracked. Dart or boss block replacement is a must if going above 500. the stock heads will hamper your gains with these and so will the upper and lower intake manifold.