After having removed the TB and intake from my LT1 for the first time i noticed the inside and the back of the TB blades are all black and it looks like they are covered with 'soot'.
Is this normal ??
Is this the result of EGR gasses ?

Thanks,

 

its normal, a combination of EGR and PCV gasses

 

Thanks for your prompt answer !

 

Completely normal. Im about 85% sure it comes from the combustion chamber through the intake valves just before they totaly close. I don't think I was paying close attention that day in class, lol. It's a good idea though to clean it off of the TB with some carb or TB cleaner and a rag.