Stock VG30DE(TT) variable Valve Timing Control (VTC) intake sprockets are non-serviceable sealed units that are notorious for leaking oil and making noise. Oil leakage occurs because the rear cover can become loose and rotate independent from the sprocket, this ruins its o-ring and eventually leads to an oil leak. The noise is typical with aftermarket higher-pressure valve springs that cause the cams to over-rotate on every valve-closing event. This over-rotation causes the VTC piston to screw itself into the VTC helix and overpower the piston return spring. As the cam continues to rotate, the valves close and the valve spring pressure diminishes to the point where the return spring slams the piston back to its stop creating the audible tick that is indicative of a noisy VTC.
By design, the VTC primary function is to advance the intake cams 20 crankshaft degrees from off idle to roughly 5800 RPM to increase torque in this RPM range. At idle and high RPM the VTC is in its static "zero advance" position which reduces overlap for smooth idle characteristics and increased torque at higher RPMs; however, at idle there is sufficient time between valve open and close events to allow the VTC piston to move its full stroke for greatest noise production. At higher RPM the noise may not be as loud due to the other competing high RPM noises, but more than likely the cams are not 100% in control of the intake valve timing and power suffers.
BDE rebuilt VTC sprockets feature a piston return spring specifically engineered to be capable of the load needed to prevent camshaft over-rotation and permit full VTC function with installed valve spring pressures up to 90 lbs. Oil leaks are eliminated by positively locating the rear cover with a dowel pin thereby preventing it from rotating.
Core Charge ($400): An additional $400 core charge applies BDE VTC Sprockets, and is charged at initial purchase. Once the Customer receives the items, they must then return their original items, in good condition (no dents or cracks are allowed back as a core credit. Core charge will not show up on internet invoice.