I'm not sure exactly what you mean by "without enchantments." But basically if you wear all 4 armor pieces, each armor piece adds a certain amount of hidden AR (armor rating), you hit a damage reduction cap of 80% at 567.
So basically you only need to improve your armor and take enough armor perks to hit that AR, with anything higher having no benefits. You don't need to enchant the armor you craft itself.
For more detail - http://www.uesp.net/wiki/Skyrim:Armor_Rating
Also improving armor adds a set amount of AR based on skills/perks, it is not a percentage based improvement. So if you have the same skill and perks, improving a scaled armor chest piece and a daedric chest piece add the same amount of AR. The base AR of the item doesn't matter in terms of how much AR is added from improvement. Your armor skill/perks though increases the end AR gap though.
Also ~83 AR is equal to 10% damage reduction.
Thanks. I wonder why they didn't make that more overt? Like, why the hidden AR.