<P> Exotic materials (titanium, magnesium, ceramics and composite) were forbidden except when present in the base model . Carbon fibre and aramid fibre were very restricted ("only one layer of fabric is used and is affixed to the visible face of the part"), except for bodywork's side protections where multiple layers of aramid fibre are allowed . </P> <P> The gear changes must be made with a mechanical system, so the paddle shifters were not allowed . However the system was re-allowed in 2015 . There was no center differential (earlier it used to be 3 differentials, with a center / 3rd differential included), but the new regulation allows only front and rear axle differential (eliminating the center differential to reduce cost), and they must be mechanical, without electronic control or hydraulic or viscous systems (from 2006 to 2010 the center differential and previously all three could be active). Minimum weight is 1200 kg empty and 1350 kg with driver and co-driver (in both cases with only one spare wheel). </P> <P> The 1.6 L turbo - charged engine was retained in the 2017 World Rally Car regulations, but the turbo restrictor diameter was increased from 33 mm to 36 mm, increasing the engine's power output from 310 bhp (223.7 kW) to 380 bhp (283.4 kW). Minimum vehicle weight was decreased by 25 kg . </P> <P> Manufacturers are also given more freedom to maximise aerodynamic performance, large brake cooling ducts in fairings forming enlarged wheel arches, and are allowed to use electronically - controlled active centre differentials, while the front and rear differentials remain mechanical . </P>

How much horsepower does a rally car have