Variable Cam Timing
Variable Camshaft Timing (VCT) is an automobile variable valve timing technology developed by Ford. It allows for more optimum engine performance, reduced emissions, and increased fuel efficiency compared to engines with fixed camshafts. It uses electronically controlled hydraulic valves that direct high pressure engine oil into the camshaft phaser cavity. These oil control solenoids are bolted into the cylinder heads towards the front of the engine near the camshaft phasers. The powertrain control module (PCM) transmits a signal to the solenoids to move a valve spool that regulates the flow of oil to the phaser cavity. The phaser cavity changes the valve timing by rotating the camshaft slightly from its initial orientation, which results in the camshaft timing being advanced or retarded. The PCM adjusts the camshaft timing depending on factors such as engine load and RPM.
For twin cam or DOHC engines, VCT was used on either the intake or exhaust camshaft. (Engines that have VCT on both camshafts are now designated as Ti-VCT.) The use of variable camshaft timing on the exhaust camshaft is for improved emissions, and vehicles with VCT on the exhaust camshaft do not require exhaust gas recirculation (EGR) as retarding the exhaust cam timing achieves the same result. VCT on the intake camshaft is used primarily for increasing engine power and torque as the PCM is able to optimize the opening of the intake valves to match the engine conditions.
The 2.0L Zetec Inline-4 used in the 1998-2003 Ford Escort ZX2, Ford Contour, and 99-02 Mercury Cougar used VCT on the exhaust camshaft. The 2002-2004 SVT Focus (ST170 in Europe) also featured VCT, but on the intake camshaft of its modified version of the 2.0L Zetec engine. In addition, the 1.7L Zetec-S engine found in the European Ford Puma was equipped with variable camshaft timing. The 6.2L V8 introduced in the 2010 SVT Raptor also uses VCT. That motor has a single cam per bank, so it is dual-equal variable cam timing.
Twin Independent Variable Camshaft Timing (Ti-VCT) is the name given by Ford to engines with the ability to advance or retard the timing of both the intake and exhaust camshafts independently, unlike the original versions of VCT, which only operated on a single camshaft. This allows for improved power and torque, particularly at lower engine RPM, as well as improved fuel economy and reduced emissions. Some Ford Ti-VCT engines use BorgWarner's Cam Torque Actuation (CTA) which utilizes the "existing torsional energy in the valve train to rotate the camshaft" instead of traditional oil pressure driven cam phasing.
Engines Using CTA System:
Engines without CTA:
- "Tests Help Check for Problems with Variable Camshaft Timing System". Auto Inc online edition, 07/10/02.
- "TWIN INDEPENDENT VARIABLE CAMSHAFT TIMING (TI-VCT) HELPS MAKE 2011 FORD MUSTANG V-6 A TRUE THOROUGHBRED". Ford Motor Company.
- "Cam Torque Actuated Phasers". BorgWarner Inc. Retrieved 2 October 2014.
- "The Ford 5.0-Liter Mustang is Back With BorgWarner Variable Cam Timing (VCT) Technology". Retrieved 2 October 2014.