At any time during a race, press Select to get a boost. When you press Select, to make sure you got a boost look at the boost gauge. Under it is a little box. Usually when driving or racing, the box does not flash. However if you press Select during a race, the box will flash and you will go faster. However this makes your engine and oil temperature rise fairly quickly. Once you see that the numbers are going up, press Select again to turn it off. This can help with quicker launches, downforce on corners (handling), and passing rivals. Pressing Select just redlines the turbo so that you get the maximum from it. If you choose to leave it on during the entire race, notice that you must go back to the garage afterwards to cool off. It is possible to reach a 101 oil temperature by doing this, which is not good.