6. It is known that the selling price of a certain model of car is 230,000 yuan per unit. A factory's total cost for producing this model of car in a year consists of fixed costs and production costs. The fixed cost for one year is 70,000,000 yuan. When producing $x$ units of this car in a year, the production cost for each car is $\frac{70-\sqrt{x}}{3 \sqrt{x}}$ ten thousand yuan $(0<x<1000)$. To ensure that the factory's sales revenue from producing this model of car in a year is no less than the total cost, the factory needs to produce at least $\qquad$ units of this car.
6.318.

If the sales revenue of this type of car produced by the factory in a year is not less than the total cost, then
$$
\begin{array}{l}
23 x-\left[7000+\frac{70-\sqrt{x}}{3 \sqrt{x}} \cdot x\right] \geqslant 0 \\
\Rightarrow x-\sqrt{x}-300 \geqslant 0 \Rightarrow \sqrt{x} \geqslant \frac{1+\sqrt{1201}}{2} \\
\Rightarrow x \geqslant \frac{601+34.6}{2} \Rightarrow x \geqslant 318 \text {. } \\
\end{array}
$$

Therefore, at least 318 of this type of car need to be produced in a year.