pick up speed
pick up steam
gather speed

After a moment, the car picked up speed once more.

The idea was to pick up enough speed to clear all three houses.

It's been doing that on an average of every four or five minutes, for hours, and now its beginning to pick up speed if anything.

He let her fall off to pick up speed and gave the order to try again.

She was still coming for me, even picking up speed.

Pick up speed and nothing goes wrong; in fact, things just keep on getting better.

After the third pass, he began to pick up speed.

He looked at the street again, and the car picked up speed.

We picked up speed and were soon on the other side.

But again he went right through, and was still picking up speed.