Turning on flex fuel
 

On a stock motor do you have to tune it or can you just add the kit and turn it on? And does it just work off the factory map tune?

There are several tables that need adjusting, so yes, you need a tune. Plenty of choices, even some guys here in the forum will be able to do it for you.

That said, you will not be able to use full E85 or anywhere near that on a supercharged motor with the stock LT4 fuel system. At the very least you should add a JMS voltage booster, and even then you'll be limited to E50-ish. Since I'm not a tuner, I can't give you accurate specifics; I'd consult a performance shop and make a plan.

Full E85 will require significant fueling changes and diminishing returns kick in strongly beyond E60-E65 anyway, you'd basically be spending a ton for the last few percent. My car has a built engine and can do up to E65, which is plenty and I'm okay with having to blend E85 and 93.