Today, most cams have mirror image (symmetric) profiles with identical positive and negative acceleration while opening and closing valves. However, some high speed (in terms of engine RPM) motors now employ asymmetrical cam profiles in order to quickly open valves and set them back in their seats more gently to reduce wear. As well, production vehicles have employed asymmetrical cam lobe profiles since the late 1940s, as seen in the 1948 Ford V8. In this motor both the intake and exhaust profiles had an asymmetric design. More modern applications of asymmetrical camshafts include Cosworth's 2.3 liter crate motors, which use aggressive profiles to reach upwards of 280 brake horsepower. An asymmetric cam either opens or closes the valves more slowly than it could, with the speed being limited by Hertzian contact stress between curved cam and flat tappet, thereby ensuring a more controlled acceleration of the combined mass of the reciprocating componentry (specifically the valve, tappet and spring).