Does anyone know if it will actually taste chocolate and how much cocoa to add? Oh please I need help

I'm not trying to be offensive...but why would you want to take a yellow cake mix and make it chocolate instead of buying a chocolate cake mix?

No offense!! That's all I have right now and am stuck with a last minute cake and not enough flour to make it from scratch like I would normally.

I've done this with a white mix and it turned out fine. Can't remember exactly, but start with about 1 cup of cocoa powder and then adjust to taste. You may need to adjust the liquid to compensate for the cocoa.

You need to add cocoa and water. I believe its 20% cocoa and 17% water. No water will mean a dry cake as cocoa drys out the moisture in a cake.

Hope that helps.

Best mix chocolate cake I've ever had:

Blue Ribbon Moist and Fudgey Chocolate Cake
Ingredients

* CAKE

1 package (18.25 ounces) plain yellow cake mix
1 1/3 cups water
1 cup chocolate syrup I use Hersheys Dark in the squeezable bottle, but any will do
1 package (3.9 ounces) chocolate instant pudding mix
1/2 cup unsweetened cocoa powder
1/3 cup vegetable oil
3 large eggs, at room temperature

http://cakecentral.com/recipes/1988/blue-ribbon-moist-and-fudgey-chocolate-cake

Thanks so much everyone!!! I can't wait to try it now!

At a guess I would subsitute 100 gm of the yellow cake mixture (or flour)with cocoa powder. Do you have any flavouring to go with the chocolate. I usually use hazelnut in my chocolate cakes. I would add coffee powder to the liquid.
This is really all guesswork, I havent actually tried it myself but go for it.

These all seem like great tips! Good luck!