My friend and I were going over this. We think it is completely obvious that Power Attack is not considered "normal weapon damage" as required under Critical Hit in the PHB 3.5 p140. At level 1, it doesn’t make much of a difference, but we went ahead and ran some numbers for level 1 and level 5. They are included below. Just as a reminder, Power Attack doubles the damage on non-light weapons that are wielded with two hands. Also, remember two-handed weapons are strength-and-a-half. As you will see below, our consensuses is that Weapon Specialization is included as “normal weapon damage” because, at a minimum, it always included when you use this weapon. Once you become SO GOOD you consider this as normal. With that being said, you’ll see below, that we think that Power Attack is not “normal weapon damage” because it can be toggled in many ways. It isn’t your normal attack. It’s like an “attack option” that you choose to use sometimes. Anyway, here are the numbers...
Critical: Method 1
This method includes the power attack in the multiplication for critical hit.
Level 1 Human Fighter w/ 18 Strength
Weapon: Scythe (2d4 x4)
Feats: Weapon Focus (Scythe), Improved Critical, Power Attack
Power Attacking at -1 to hit, +2 to damage:
+1 BAB +4 STR +1 WF -1 PA = +5 TH
2d4 +6 STR +2 PA = 2d4+8 DMG
(2d4+8)x4 DMG = 8d4+32 DMG
(Minimum: 40 DMG, Average: 48 DMG, Maximum: 64 DMG)
Level 5 Human Fighter w/ 19 Strength
Weapon: Scythe (2d4 x4)
Feats: Weapon Focus (Scythe), Improved Critical, Power Attack, Cleave, Combat Expertise, Weapon Specialization (Scythe)
Power Attacking at -5 to hit, +10 to damage:
+5 BAB +4 STR +1 WF -5 PA = +5 TH
2d4 +2 WS +6 STR +10 PA = 2d4+18 DMG
(2d4+18)x4 DMG = 8d4+72 DMG
(Minimum: 80 DMG, Average: 88 DMG, Maximum: 104 DMG)
Critical: Method 2
This method excludes the power attack in the multiplication for critical hit.
Level 1 Human Fighter w/ 18 Strength
Weapon: Scythe (2d4 x4)
Feats: Weapon Focus (Scythe), Improved Critical, Power Attack
Power Attacking at -1 to hit, +2 to damage:
+1 BAB +4 STR +1 WF -1 PA = +5 TH
2d4 +6 STR + 2 PA = 2d4+8 DMG
((2d4+6)x4)+2 DMG = 8d4+26 DMG
(Minimum: 34 DMG, Average: 42 DMG, Maximum: 58 DMG)
Level 5 Human Fighter w/ 19 Strength
Weapon: Scythe (2d4 x4)
Feats: Weapon Focus (Scythe), Improved Critical, Power Attack, Cleave, Combat Expertise, Weapon Specialization (Scythe)
Power Attacking at -5 to hit, +10 to damage:
+5 BAB +4 STR +1 WF -5 PA = +5 TH
2d4 +2 WS +6 STR +10 PA = 2d4+18 DMG
((2d4+8)x4)+10 DMG = 8d4+42 DMG
(Minimum: 50 DMG, Average: 58 DMG, Maximum: 74 DMG)