Usage of "How" for referring to amount or quality instead of proposing questions

Question

As I know, I can start an interrogative sentence with "How" for proposing questions like:

1. How fast does this car go?
2. How much does this car cost?

Can I start a declarative sentence or a phrase with "How" to refer to amount or quality of something?

3. How fast this car goes has not been tested. (I want to say the amount of speed that this car can go has not been tested.)

4. How much this car costs depends on options. (I want to say the amount of money that this car costs depends on options.)

Are the third and fourth sentences grammatically correct? Do they convey the meaning that I want to say?

Answer 1

Yes, as BillJ says in the comments, 3 and 4 are correct. However, in terms of common speech, they do sound slightly unnatural to native speakers. This problem is usually solved by putting a clarifying word in front of "how."
Commonly:

3: Precisely how fast this car goes has not been tested.

4: Exactly how much this car costs depends on options.

Or, they sound more natural in a future tense:

3: How fast this car goes has not yet been tested.

4: How much this car costs would depend on options.