Anyone with a Facebook account will have seen the words ‘VTEC kicked in, yo!’emblazoned on their news feeds at least 10 times. It’s a phrase that has wormed its way into everyday conversation and has increasingly been used to caption car crash pictures, car jump images, and of course, scenes from that movie…
While most of us understand that a car gets faster when VTEC kicks in, many may not know why and how this occurs. In case you’re a little rusty on your VTEC knowledge, here is everything you need to know, plus a little extra for diehard VTECers.
1. What is VTEC?
VTEC is an acronym (a bad one at that) for Variable Valve Timing and Lift Electronic Control. Found only in a selection of Honda engines, the basic idea of VTEC is that itgives an engine the properties of multiple camshafts. (A camshaft is a shaft with multiple lobes. When the camshaft spins, the lobes – called cams – open and close intake and exhaust valves in time with the motion of the piston).
The benefit of having an engine that possesses the properties of multiple camshafts, is that just one camshaft is able to open the intake and exhaust valves more and for a longer duration at high RPMs. This means the engine gets more air flow which allows more power to be harnessed.
Just like we need more air in our lungs when we run, VTEC gives an engine more air to breathe at higher revs too.
How does VTEC work?
A camshaft that you’d find in a VTEC engine has both larger and smaller lobes (or cams). A larger central lobe is flanked either side by one smaller lobe.
At low RPMs, the lobes which push the exhaust and intake valves open and closed by means of rocker arm (see video) are the two smaller ones. This limits how much the valves open, which in turn limits the amount of air that the engine gets; this is good for efficiency. At this point, the larger central lobe and central rocker arm are inactive.
At higher RPMs, by contrast, a solenoid injects more oil into the rocker arm whichforces two pins in the larger central rocker arm outwards. These pins lock the central rocker arm into the two flanking rocker arms, so that with every revolution of the larger central lobe on the cam shaft, the central rocker arm opens the valves more, allowing more airflow into the engine for enhanced performance.
When the large central lobe is active (when VTEC kicks in), the two smaller lobes do not control the opening and closing of the intake and exhaust valves.
Pros and cons of VTEC
Pros: VTEC engines are very reliable, offer enhanced fuel economy and more power at higher revs. When VTEC is engaged, the engine note also changes for the better.
Cons: The main disadvantage of VTEC is that it is engaged from (on average) 5000-6000 RPM, the area of the rev range that drivers explore rarely. For that reason, VTEC is not necessary for many cars and their drivers. Nice to have just in case, however…
1. There are 3 types of VTEC: VTEC-E, 3-stage VTEC and I-VTEC.
This increases combustion efficiency at low RPMs while maintaining mid-range performance. Instead of three intake lobes, VTEC-E has two different intake cam profiles per cylinder (a small cam and a normal cam). At low RPMs, the small cam opens one of the two intake valves by a very small amount, which forces most of the intake charge through the other valve with the normal cam. When this happens, a leaner fuel mixture results, which is good for economy.
When VTEC is engaged, pins connect the rocker arms together (via solenoids) which means both intake valves are controlled by the normal camshaft lobe, the same you would find on a non VTEC camshaft. For this reason, VTEC-E engines do not offer performance benefits higher up in the rev range.
This combines the low RPM combustion efficiency of VTEC-Es with the high RPM performance benefits of a VTEC engine. At low RPMs, one intake valve opens a little, while the other opens normally. This is called 12-valve mode and boosts efficiency and low-end torque. In the mid range (3000-5400 RPM), one VTEC solenoid is engaged, which locks the second valve onto the first valve’s camshaft lobe – this improves mid-range torque. Finally, at between 5500 and 7000 RPM, another solenoid locks the central rocker arm into its flanking rocker arms, which means the central, larger lobe controls the valves for increased performance.
I-VTEC (meaning intelligent-VTEC) has continuously variable timing of camshaft phasing on the intake camshaft of DOHC VTEC engines. An I-VTEC intake camshaft is capable of advancing between 25 and 50 degrees, which is controlled by an adjustable cam sprocket. The benefit of I-VTEC engines is to further optimise torque output.
2. A world’s first:
VTEC was the world’s first engine mechanism that simultaneously changed the valve timing and lift on the intake and exhaust sides. The man who is known as the‘father of VTEC’ is Ikuo Kajitani, who was employed in the first design department at Honda’s Tochigi R&D facility. He was given the task of producing an engine with 100bhp per litre. VTEC was the result.
3. Honda S2000’s previous record:
Until the introduction of the Ferrari 458, the S2000 boasted the highest horsepower per litre record for a naturally aspirated (non wankel) production car, at 118.5bhp (237bhp in total). Its record would only be taken away from the S2000 by the 458, which produced 123.78bhp per litre from its highly strung 557bhp 4.5-litre V8.
Different car makers use similar tech:
Honda is not the only manufacturer to use variable valve timing to enhance economy and/or increase performance. Here are six different versions of the same technology.
BMW = VANOS Fiat = MultiairGM = DCVCPMazda = S-VTNissan = VVLToyota = VVT-i/ VVTL-i
In this article, we’ve discussed what VTEC is and how it works, the popularity of VTEC and its pros and cons. We’ve also explored some advanced info (including the different types of VTEC) and how variable valve timing is applied by different manufacturers. Now there’s no excuse to be like this guy…