The appearance of World Rally Championship (WRC) cars will change as of 2017; they will grow wider and longer, as well as more powerful. All cars will have more focus on aerodynamics, gaining 55mm in width and longer front / rear overhangs.

The official release announcing this also informs us of the boost in power these cars are going to get – from 300 hp up to 360 hp courtesy of larger turbos on their 1.6-liter engines. Weight is also set to drop by 25 kg / 55 lbs and this should all come together and produce some more aggressive cars.
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https://www.carscoops.com/2015/07/wrc-news-whiff-of-group-b-spirit-to-be/