way to the early 1990s. One main reason OHV engines have lower redlines is valve float. At high speeds, the valve spring simply cannot keep the tappet or roller on the camshaft. After the valve opens, the valve spring does not have enough force to push the mass of the rocker arm, pushrod, and lifter down on the cam before the next combustion cycle. Flathead engines can have even lower redlines; for example, the Universal Atomic 4, commonly used as auxiliary power on sailboats from the 1950s to the 1980s, has a redline of just 3500 RPM. Overhead cam engines eliminate many of the components and moving mass, used on OHV engines. Lower redlines, however, do not necessarily mean low performance. Motorcycle engines can have even higher redlines because of their comparatively lower reciprocating mass. For example, the 1986–1996 Honda CBR250RR has a redline of about 19,000 rpm. Higher yet have been the redlines of some Formula One cars, with engine speeds reaching over 20,000 rpm on the Cosworth and Renault 2.4-liter V8 engines during the 2006 season. Rev-limiter and implementation Most modern cars have computer systems that prevent the engine from straying too far into the redline by cutting fuel flow through the fuel injectors/fuel rail (in a direct-injected engine)/carburetor or by disabling the ignition system until the engine drops to a safer operating speed. This device is known as a rev-limiter and is usually set to an RPM value at redline or a few hundred RPM above. Most Electronic Control Units (ECUs) of automatic transmission cars will upshift before the engine hits the redline even with maximum acceleration (The ECU in a sports car's automatic transmission will allow the engine to go nearer the redline or hit the redline before upshifting). If manual override is used, the engine may go past redline for a brief amount of time before the ECU will cut power to pull it back or auto-upshift. When the car is in top gear and the engine is in redline (due to high speed), the ECU will cut fuel to the engine, forcing it to decelerate until the engine begins operating below the redline at which point it will release fuel back to the engine, allowing it to operate once again. However, even with these electronic protection systems, a car is not prevented from redlining through inadvertent gear engagement. If a driver accidentally selects a