Sprint cars have very high power-to-weight ratios, with weights of approximately 1,400 pounds (640 kg) (including the driver) for the 410 sprint car class. Power outputs of over 900 horsepower (670 kW) are commonplace for these machines, which, when combined with their light weight, gives them a power-to-weight ratio comparable to an F1 car. Typically, they are powered by a naturally aspirated, methanol injected over-head valve V8 with an engine displacement of 410 cubic inches (6. 7L) capable of engine speeds approaching 9000 rpm. Depending on the mechanical setup (engine, gearing, shocks, etc. ) and the track layout, these cars can achieve speeds in excess of 160 miles per hour (260 km/h). A lower budget and very popular class of sprint cars uses 360 cubic inch (5. 9L) engines that produce approximately 700 horsepower (520 kW). Sprint cars do not utilize a transmission, they have an in or out gear box and quick change rear differentials for occasional gearing changes. As a result, they do not have electric starters (or even electrical systems other than a magneto / ignition) and require a push to start them. The safety record of sprint car racing in recent years has been greatly improved by the use of roll cages, and especially on dirt tracks, wings, to protect the drivers.