When the first VTEC engine was available in the States, I thought it was so high tech I was scared to touch it. The thought of having two different cam profiles per cam was amazing, I never would have thought it was possible and I figured it must have been some sort of high tech computer that allowed the secondary cam profile to kick in. As time went by, I eventually became familiar with the way it works and I realized it's not as high tech as most people originally thought. I remember when an all-motor drag car producing 180 hp on race gas was considered ungodly, yet today we see street Hondas putting out 200 on pump gas. Finding horsepower in VTEC engines is still an ongoing process, and one of the keys to making horsepower is found in degreeing cam sprockets. Cams and sprockets became a necessity to unleashing massive horsepower. Today, on the newer Hondas, we have a new "high tech" issue dealing with the sophisticated valvetrain, but this time around it really is scary to play with. The technology I speak of is VTC (Variable Timing Control).
To give credit where credit is due, this is actually not the first time we've seen this on an engine, Toyota used this technology long ago on the Japanese spec, 20-valve 5AG engine in '92. Of course, the technology has since been adapted on the J-spec Nissan SR20s, and even on the U.S.-spec Celica and Subaru's STi, but now Honda has adapted it to a few of its K-series engines. VTC allows the computer to adjust an engine's intake cam sprocket at any RPM level. Variable Timing Control completely eliminates the use of an intake sprocket. Keep in mind that this was not added primarily for performance, but also features emission and gas mileage issues. This eliminates the use of an aftermarket adjustable cam sprocket. Technically, with a newly designed engine, which uses only VTC on the intake sprocket, you can put an adjustable sprocket on the exhaust side. But it's going to be some time before somebody figures out how to time the two cams correctly without hitting the valve. The problem is the fact that the computer can control the intake cam with up to 25 degrees of intake advance or retard throughout any RPM level. Knowing this, it makes adjusting the exhaust sprocket a very sensitive issue. The trick is to know how it works mechanically first.
Using the same concept as VTEC, VTC is controlled by using the engine oil as hydraulic fluid to control the intake cam sprocket. Imagine VTC as if it were a lowrider on hydraulics. By using a hydraulic pump, the height of the vehicle can be lowered or raised from its regular position. Now imagine the shock setup for the hydraulic fluid. When hydraulic fluid is pumped into one side of a shock's chamber, fluid is removed from the opposite chamber. This is what adjusts the vehicle's ride height. Using the same concept, imagine a cam sprocket that also has a two-sided chamber (the hydraulic shock theory). By using the engine's oil pressure and an electronically controlled oil control valve (the hydraulic pump), oil can be used to fill one of the sprocket's chamber's while the other chamber is relieved of oil. Keep in mind only a certain amount of oil is released to make up the difference on the opposite side, which has more oil.
The ECU side of how VTC works is much trickier than the mechanical unit itself. We all know the computer controls everything on the engine, and in the VTC's case it is the brain for the oil control valve. Going back to our lowrider theory, the hydraulic pump and solenoids would be a combination of engine oil pressure and oil control solenoid. The ECU is the guy controlling the switches to raise or lower the vehicle. Basically, by applying voltage to one of the solenoids (via the operator's finger on the switch) the pump is activated to send fluid to the one chamber of the shock. By flipping the switch in the opposite direction fluid is released from the same side while fluid is pumped into the opposite chamber. There is a big difference from this theory to the way VTC works. The transfer of fluid is sent not by the flip of a switch but rather a series of signals, almost like flipping a light switch a thousand times to maintain a certain level of light. For the VTC, this is called a square wave pulse width signal. The main reason the signal is carried out like this is because the sprocket needs to be accurate up to one-degree increments. The last thing you want is to bend a valve due to the sprocket being off at the wrong time.
The trick behind VTC is how to control it to benefit in the horsepower department. A few companies are able to control variable cam sprockets on non-Honda vehicles, but as of right now Hondata is the only company to ROM tune a VTC Honda ECU correctly. According to Doug McMillian, from Hondata, "If you plan on going forced induction and you're not able to control the VTC, you'll not get the real power a turbo or supercharger is able to produce due to the computer's ability to adjust the cam sprocket." Just like when VTEC came out, it's only a matter of time when we see more companies produce piggyback computers to control VTC. But for now, this "high tech" gizmo is the key to making power on the K-series engine. Until then, you know I'll keep trying to pick the lock for VTC power.