Engineers and designers have spent decades trying to figure out ways to get more power out of an engine. One question that all engineers have is what the motor will be used for – will it be for an economical commuting car, will it go into a supercar or will it be used in a wagon where torque is more important than raw power. Subsequently, the design of the motor will differ even though the basic concepts are the same.
For some engineers, they take a motor and re-work it for a different purpose. Examples would be the Dodge Viper V10 that was also put into the Dodge Ram truck and the Bristol Fighter, both vehicles used reworked internals from the original. Another example was the Ferrari-Maserati F136 motor that was jointly developed by the two partners and was fitted to a range of vehicles from both manufacturers. The Maserati version was designed for grand touring with a cross plane crank and the Ferrari version had a flat plane crank and was designed for higher power delivery.
One mode of balancing the power delivery between normal driving and hard performance driving is the use of variable valve timing – the F136 motor deployed this technology and my old Honda S2000 certainly used it. In fact the similarities between the F136 and Honda’s F20C motor don’t stop there – both were double overhead cam with four valves per cylinder. The Honda engine was half the size, literally to the Italian motor.
The base concept of variable valve timing is clever, at lower traffic speeds, the camshaft uses one shaped lobe to provide efficient, economic delivery of power with improved emissions. When engine speeds rise, a second cam lobe is used with a more aggressive shape, providing more power at the higher revs.
In a bit more detail, specifically with regards to the Honda VTEC (short for Variable Valve Timing & Lift Electronic Control) motor, the camshaft had two lobes per valve with a solenoid and locking pin. When the engine speed reached around 6,000 revs, the solenoid moved the camshaft to engage and lock the “power” lobe in place. There was a noticeable push at that point and on track it was necessary to try and keep the motor above 6,000 revs to retain that lobe. Once the engine switched back to the “economy” lobe, the motor lost a chunk of torque.
The funny thing about variable valve timing is that the original concept goes all the way back to the early steam engine. At that time, the engineers wanted to release steam at different times to allow for pressure release or power consumption. Like many technologies, it was taken up by the aero industry before it went into automotive uses. Bristol used it in an aero engine in the 1920s and a US patent for an automotive use was also lodged that decade.
Porsche applied for European patents in the 1950s yet it was FIAT that got a functioning system patented in the late 1960s. Alfa Romeo were the first to get it into a production car in 1980 on their series 2 Spider 2000. Amazingly it took 80 years to get it into road cars, then again, it is one of many ideas that were researched to get the balance of power and economy that the manufacturers wanted.
Variable valve timing could also include early or late opening and closing of valves to improve gas flows, again based on power needs. The really whizzy design piece is the shape of the cam lobe coupled with the ability to make the lobes switch at high speeds without destroying the motor.
If you see badging such as VTEC (Honda), VVTi (Toyota), MultiAir (FIAT), MIVEC (Mitsubishi) or VarioCam (Porsche), then you have a car with variable valve timing!