Variable valve timing

VTEC (Variable Valve Timing and Lift Electronic Control) is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda engineer Ikuo Kajitani^[1][2], and was the first system of its kind

MIVEC (Mitsubishi Innovative Valve timing Electronic Control system)^[1] is the brand name of a variable valve timing (VVT) engine technology developed by Mitsubishi Motors. MIVEC, as with other similar systems, varies the timing of the intake and exhaust camshafts which increases the power and torque output over a broad engine speed range while also being able to help spool a turbocharger more quickly.

MIVEC was first introduced in 1992 in their 4G92 powerplant, a 1,597 cc naturally aspiratedDOHC 16 valve straight-4.^[2] At the time, the first generation of the system was namedMitsubishi Innovative Valve timing and lift Electronic Control.^[3] The first cars to use this were the Mitsubishi Mirage hatchback and the Mitsubishi Lancer sedan. While the conventional 4G92 engine provided 145 PS (107 kW; 143 hp) at 7000 rpm,^[4] the MIVEC-equipped engine could achieve 175 PS (129 kW; 173 hp) at 7500 rpm.^[5] Similar improvements were seen when the technology was applied to the 1994 Mitsubishi FTO, whose top-spec GPX variant had a 6A12 1997 cc DOHC 24 valve V6 with peak power of 200 PS (147 kW; 197 hp) at 7500 rpm.^[6] The GR model, whose otherwise identical powerplant was not MIVEC-equipped, produced 170 PS (125 kW; 168 hp) at 7000 rpm by comparison.^[7]

VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timingtechnology developed by Toyota, similar in performance to the BMW's VANOS. The Toyota VVT-i system replaces the Toyota VVT offered starting in 24 December 1991 on the 5-valve per cylinder 4A-GE engine. The VVT system is a 2-stage hydraulically controlled cam phasing system. The Toyota motors CEO has been reported to have said, "VVT is the heart of every modern Toyota!"^{[citation needed]}

VVT-i, introduced in 1996, varies the timing of the intake valves by adjusting the relationship between the camshaft drive (belt, scissor-gear or chain) and intake camshaft. Engine oil pressure is applied to an actuator to adjust the camshaft position. Adjustments in the overlap time between the exhaust valve closing and intake valve opening result in improved engine efficiency.^[1] Variants of the system, including VVTL-i, Dual VVT-i, VVT-iE, andValvematic

CamPro CPS and VIM engine

The Campro CPS 1.6L engine inside theProton Satria Neo CPS R3 engine bay.

The CamPro CPS engine uses a variable valve lift system (Cam Profile Switching system) and a variable length intake manifold (VIM; not to be confused with the stand-alone IAFM used in the 2008 Proton Saga) to boost maximum power and improve the CPS engine's torque curve over the standard DOHC CamPro engine.

The engine's Variable-length Intake Manifold (VIM) switches between a long intake manifold at low engine speeds and a short intake manifold at higher engine speeds. Proton cars use a longer intake manifold to achieve slower air flow; as it was found that promotes better mixing with fuel. The short intake manifold allows more air in faster. This is beneficial at high RPMs.

The Cam Profile Switching (CPS) system uses a trilobite camshaft to switch between two different cam profiles. One cam profile provides low valve lift, while the other cam profile has a high valve lift. The low valve lift cam profile is used at low to mid engine speeds to maintain idling quality and reduce emissions, while the high lift cam profile is used when the engine is spinning at mid to high engine speeds improve peak horsepower and torque. Unlike the other similar variable valve timing systems such as the Honda VTEC, the Toyota VVT-i and the Mitsubishi MIVEC which use rocker arm locking pins to change the valve timing, the CPS system uses direct-acting tappets with locking pins to change the valve timing and lift profile.

VIM switches from the long to short runner at 4,800 rpm, while the CPS system switches over at 3,800rpm (4,400 rpm in the Proton Satria Neo CPS^[3]). The result is 125 bhp (93 kW; 127 PS) at 6,500 rpm and 150 N·m (110 ft·lbf) of torque at 4,500 rpm compared to the non-CPS CamPro’s 110 bhp (82 kW; 112 PS) at 6,000 rpm and 148 N·m (109 ft·lbf) of torque at 4,000 rpm. Proton claims that there is better response and torque at low engine speeds of between 2000 - 2500 rpm.

The new CPS engine first made its debut in the face-lifted Proton Gen•2 launched in Thailand in 2008,^[4] and made its first Malaysian debut in the Proton Waja CamPro 1.6 Premium (CPS).