What is the max for each stat before you start getting into the minor powers or major? Where in the book do you find each?
I'm going to answer the question for the edition I own: Heroes Unlimited, Revised 2nd Edition.
On page 15-16, the rules list different limits for different attributes:
- Mental Endurance, IQ, Mental Affinity, and Physical Beauty max out at 30 for mortals.
- Physical Strength has a limit of 40 for normal humans ("including aliens and mutant animals" - R.A.W.)
- Physical Prowess has a maximum of 50 for all characters, mundane or supernatural.
- Physical Endurance and Speed have no limits.
A very important clarification: this is how high the attributes can be created and be considered mundane. Nothing in the rules says that the attributes must be lowered to mundane levels before adding superpowers.
To answer how high you can get in chargen without invoking minor and major powers:
- The core 8 attributes all have the potential of a base value of 30 - a high initial roll and making both exploding rolls.
- Taking all 7 physical skills that improve attributes (Acrobatics, Athletics, Body Building & Weight Lifting, Boxing, Gymnastics, Running, and Wrestling) and maxing out the roll for each increase your bases to: IQ 30, ME 30, MA 30, PS 40, PP 32, PE 35, PB 30, Spd 52, +84 SDC.
But why stop there? Several power categories are explicitly defined as being mundane. We could see what they give us...
- Physical Training's Endurance and Strength focus would raise the aforementioned limits to PE 43, PB 34, Spd 58, add 36 Hit Points, and add 150 SDC, given maximum rolls, and apply the Supernatural quality to their strength.
- Physical Training's Agility and Speed focus would raise the limits to PP 36, PB 34, Spd 80, add 18 hit points, and add 70 SDC, given maximum rolls.
- All Hardware classes are explicitly mundane, but add no attributes besides 30 or 35 extra SDC.
- Special Training's Ancient Master focus would raise the limits to MA 38, add 36 hit points, and add up to 216 SDC. (They are limited to five physical skills due to their unique combat bonuses, but they can also choose one super power that represents decades of training - due to the phrasing of the question, I am ignoring these bonuses.)
- Special Training's Secret Operative would raise the limits to MA 36, PS 46, PP 36, PE 41, and add 12 HP and 100 SDC.
- Special Training's Stage Magician would raise the limits to MA 36, PP 38, PB 34 PB, and add 30 SDC.
- Special Training's Super Sleuth would raise the limits to IQ 31, ME 36, and MA 34, as well as adding 40 SDC. (The Super Sleuth focus for Special Training seems to be the only way R.A.W. to increase intelligence without supernatural powers, and even then, it's only one point.)
Note that this is only counting the core rulebook. Many of the mundane classes suggest options from Ninjas & Superspies, which can go even higher and yet still count as 'mundane'.