There not exspensive to get good power from , set of forged pistons and a nice head and cam and some 45s will see 140-160 bhp depending on head and cam , ive just gone over board , steel components dont give more power there just stronger. bigger capacity will give you a little more power , cheaper than a standard 2.0 zetec on 45s as i said above with conversion cost with similar if not more power , unless you go for the st170 engine if iam correct
But 180-190+ will hurt my wallet nick you any closer to getting back "that" engine for "that" car