Do I do something wrong or don't the tempering bonus for dragon weapons work.
Finally gotten smitting to 100 and made some dragon weapons, however after tempering they did less damage than my elven ones.
Tempered them in one session so I it's not that I'm not wearing smiting gear.

Enchanted gear to boost smithing, and/or potions can buff you for better tempering.
Smithing perks also come into play here as well.

I know, I took the light armor path alll the way up to dragon smithing, so I have the perk both for elven and dragon, the dragon bow do 70 damage and the elven 93. so it looks a lot like I do not get the tempering bonus.

Most of the weapons seem to be dragonbone (heavy) as opposed to dragonscale (light).
This may be the reason if they stuck to the pattern used in armor.

Should not matter who way you came from as only the perk itself gives the tempering bonus.
Will try to check in the editor then home.
Fells a bit like I vasted an perk.

That's strange. My drahonbone all were way stronger.

Maybe you popped a stronger potion when smithing the Elven?

Found it, the mod Legendary smithing updgrades is not dawnguards compatible http://skyrim.nexusmods.com/mods/1690