Here’s a close look at a 4.6-liter Three-Valve engine’s infamous “three valves.” The SOHC bullet features two intake and one exhaust valve, versus a standard head’s intake/exhaust pair only (or Four-Valve’s two pairs of each). Variable Cam Timing is a feature of the ’05-’10 Mustang GTs’ Three-Valve engines. VCT is used for modifying the cams’ lift, duration, and timing (both intake and exhaust) while the engine is in operation. While it’s a great feature for maximizing the engines performance and fuel economy, VCT will not work with the Two-Valve processor. Thus, locking out the Three-Valve’s valve events is required for this transplant operation.