I wanted to put together a thread about the new valvetrain technologies that are improving power, efficiency and emissions on cars these days. I also included older technologies so you can see how things have moved forward.
The original VTEC was a big step. Back in the dark ages, you had to sacrifice low RPM torque and drivability for high RPM power. Bigger cams mean more valve lift, and more valve overlap, but automakers couldn’t do this, because the car would run really rough at low RPMS, and gas mileage would be horrible.
Honda came up with the idea to add more lobes to the camshaft. The idea was to have the regular cam lobes for lower RPMS, but once you reached a certain RPM, the engine would switch to the other set of lobes on the cam, which were bigger and provided more lift, which keeps the valves open longer and open deeper into the cylinder. This allows for more air & fuel into the combustion chamber, thus making more power. Honda has 2 and even 3 stage VTEC systems. One thing to note, is that the original VTEC system, is not a variable valve timing system. It is a variable LIFT system.
SOHC vs. DOHC VTEC
SOHC VTEC = Applies the lobe changes to just the intake valves.
DOHC VTEC = Applies the lobe changes to both the intake and the exhaust valves. The S2000 is a DOHC VTEC engine. I believe it is only a 2 stage and makes an impressive 120 HP per liter. (The original S2000 had a 2.0 liter engine and still made 240HP)
i-VTEC was introduced to improve on the original VTEC system. It adds variable valve timing to the VTEC system. Now Honda not only has variable lift control, but also can adjust the timing of when the valves are opened. The addition of the VVT system to i-VTEC also smoothes the transition between lobes. It is also intelligent and can change valve timing depending on load, RPM and other environmental variables.
Toyotas VVT-I system is a much simpler technology than VTEC. There is no lift control with VVT-i. All VVT-i does is change the timing on when the intake valves are opened. The “i” in VVT-i stands for “Intelligent.” The system is intelligent because it varies the valves timing depending on load, engine temp, rpm, etc. By varying the valve timing, low end torque and high RPM horsepower are achieved. The intake valves are continuously variable throughout the RPM range. Meaning the VVT-i system can retard or advance intake valve openings throughout the whole RPM range. Even though VVT-i doesn’t have quite the same performance benefits as VTEC or i-VTEC, it is a cheaper system and has a much smoother power band than VTEC.
Dual VVT-i applies this technology to both the intake and exhaust valves. This allows for more valve overlap in the higher RPMS, which improves power and emissions. The illustration below shows the amount of valve overlap with just intake VVT-i.
With the addition of this technology on the exhaust valves, this allows for more valve overlap. Here is an example with BMW’s Double-VANOS system. You can see there is more valve overlap when compared with just the intake only VVT-i system.
The 2.0 liter engine in the Altezza code named BEAMS is a dual VVT-i engine that makes an impressive 110 HP per liter.
VVTL-i adds the lift control to the VVT-i system. The “L” stands for “Lift.” Basically, i-VTEC and VVTL-i are very similar, since they both can adjust lift and valve timing.
The BMW VANOS system is a variable valve timing system just like VVT-i. This technology can be found on most of the current models from BMW. This VVT system only functions on the intake valve. One thing to note is on most BMW engines that use single VANOS, the timing of the intake cam is only changed at two distinct rpm points, while on the double-VANOS system, the timing of the intake and exhaust cams are continuously variable throughout the majority of the rpm range.
Double VANOS adds this technology to the exhaust valves. Double-VANOS improves low rpm power, flattens the torque curve, and widens the powerband for a given set of camshafts. The double-VANOS engine has a 450 rpm lower torque peak and a 200 rpm higher horsepower peak than single-VANOS, and the torque curve is improved between 1500 - 3800 rpm. At the same time, the torque does not fall off as fast past the horsepower peak. This technology can be found in the current M3 and will be integrated in to the new Inline 6 motors for the 2006 3 series.
This is a new technology from BMW. Valvetronic engines use a combination of hardware and software to eliminate the need for a conventional throttle mechanism. BMW has one upped Honda with an infinite variable lift system. The Valvetronic engine replaces the function of the throttle butterfly by using an infinitely variable intake valve lift.
“Fuel injection systems monitor the volume of air passing through the throttle butterfly and determine the corresponding amount of fuel required by the engine. The larger the throttle butterfly opening, the more air enters the combustion chamber.”
“At light throttle, the throttle butterfly partially or even nearly closes. The pistons are still running, taking air from the partially closed intake manifold. The intake manifold between the throttle and the combustion chamber has a partial vacuum, resisting the sucking and pumping action of the pistons, wasting energy. Automotive engineers refer to this phenomenon as "pumping loss". The slower the engine runs, the more the throttle butterfly closes, and the more energy is lost.”
“Valvetronic minimizes pumping loss by reducing valve lift and the amount of air entering the combustion chambers.”
“Compared with conventional twin-cam engines with finger followers, Valvetronic employs an additional eccentric shaft, an electric motor and several intermediate rocker arms, which in turn activates the opening and closing of valves. If the rocker arms push deeper, the intake valves will have a higher lift, and vice-versa. Thus, Valvetronic has the ability to get deep, long ventilation (large valve lift) and flat, short ventilation (short valve lift), depending on the demands placed on the engine.”
“Valvetronic reduces maintenance costs, improves cold start behavior, lowers exhaust emissions, and provides a smoother running engine. Valvetronic does not need specific fuel grades or fuel qualities because of its fine atomization of fuel.”
“The entire Valvetronic system is pre-assembled and inserted as a module into its position in the cylinder head. Valvetronic engines are built at BMW's brand new engine plant at Hams Hall near Coventry, England.”
“Because Valvetronic allows the engine to breathe more freely, fuel consumption is reduced by 10%. The fuel savings are greatest at lower engine revs. Valvetronic is an important element in BMW's aim of meeting the 2008 carbon dioxide fleet requirements of 140 gm/km.”