Cake burnt on top using both elements on top and bottom.

Yes, I would suggest you only use the bottom element when baking the actual cake. Using both elements is generally used for pre-heating the oven, or to brown the top of a dish. Maybe use the top element to bring the oven up to temperature, then turn it off when you put the cake/brownies in the oven.

It depends on your oven and how bad the result is.

I suggest making different tries:

1. use only the bottom element
2. use both element and cover your cake with foil when you have the desired color on top to prevent over-cooking
3. use a pizza stone to keep an even temperature in your oven

I had the same problem and tried all those solutions. They all have pros and cons and depends on the result you want to achieve.