What's so special about VTEC?

Arif · Aug 05, 2020 05:00 PM

Mention VTEC and images of an uncouth, loud, and high-revving Honda Civic speeding down the highway might appear in your mind. VTEC is Honda’s signature technology that dates all the way back to 1983. Uttering VTEC itself might even inject some imaginary adrenaline into your veins if you have any idea what VTEC feels like.

Disclaimer: This article focuses on the fundamental concept of VTEC. Things like i-VTEC and VTC are will be discussed in a different entry.

VTEC is a technology developed in the 80s that was simple yet remarkable. Although other Variable Valve Lift (VVL) systems have been invented (e.g. Fiat), none of them had used the lockable rocker arms and the dual profile camshaft like Honda's VTEC.

Now, while VTEC may be a familiar term among car enthusiasts, not many people actually understand what VTEC is. And that’s why we’re writing this article for you - so you can understand and appreciate it. Let’s begin…

Q: First question, what on earth is VTEC?

A: VTEC stands for Variable Valve Timing & Lift Electronic Control. What makes VTEC a little bit special is the use of Variable Valve Lift (VVL).Yes, other brands have VVL too. In fact Fiat patented a form of VVL first (US Patent 3,641,988). We'll to get to that later.

Q: What is valve lift?

A: As the piston moves up and down in the engine, valves open and close to allow air in (intake valve) and allow air out (exhaust valve). The valves are controlled by camshafts. Valve lift is a measure of how much the valve opens (aperture). The bigger the valve lift, the bigger the opening, the more air and fuel gets pumped in.

Q: What is variable valve lift (VVL) then?

A: Normally, valves only have one aperture. VVL means that the valve can open at several distinct apertures (usually two).

There are other methods to achieve VVL, but Honda's VTEC combines lockable rocker arms and dual profile camshafts.

This is what the VTEC dual profile camshaft looks like…

Note that the second cam profile is much larger, causing the valve to open more.

At higher RPMs, the engine operates with the larger cam profile. At low RPMs and low load, the engine operates with the first cam profile.

How does the engine select which cam profile to use?

Oil pressure controls a synchronizing pin that locks the rocker arms. When locked, the rockers will follow the larger cam profile and thus create a bigger valve lift. When unlocked, the rocker arms follow the smaller cam profile. That’s it.

That's it. That's the fundamental of Honda's VTEC. i-VTEC just combines VTEC with Honda's VTC (Variable Timing Control).

Q: But VTEC looks so simple... What’s the big fuss about it?

A: Yes,the concept of VTEC is simple. Different cam profiles will make an engine behave differently. High performance cars usually have bigger valve lifts to allow as much air in as possible. Fuel efficient cars usually have smaller valve lifts.

VTEC (in the 1980s) allowed you to have two engine characteristics merged into one engine. That’s the big fuss about it. And VTEC, unlike other VVL systems, combines lockable rocker arms with dual profile camshafts...

When you wanted to be fuel efficient, a smaller cam profile was selected. When you wanted more power, a larger cam profile was selected. Simple as that.

At the core of it, the biggest difference VTEC made was introduce Variable Valve Lift (VVL) in a production car by using two distinct cam profiles on a single camshaft.

Q: Isn’t VTEC just Variable Valve Timing (VVT)?

Variable valve timing on a motorbike engine

A: No. VVL and VVT are two different things. Honda's VVT system is called VTC (Variable Timing Control). Variable valve timing is basically the variable phasing of the valve. The valve opening is either advanced or retarded in a VVT system. The valve lift is not changed in a VVT system.

Q: When did Honda come up with the VTEC?

A: In the 80s. The concept of VTEC was first used on a motorcycle – The Honda CBR400, in 1983. At that time, it was referred to as the Revolution-Modulated Valve Control (REV).

The first car to use the VTEC system would be the 1989 Honda Integra XSi. The Honda company was a tad over 40 years old when its most famous technology was invented. 

Q: Meh, other companies have VVL too. What's different about VTEC?

A: Porsche had filed a patent for VVL back in 1959 but is unknown whether the system had been tested at all. Their system utilised an oscillating cam to change the valve lift. Fiat later developed a VVL prototype that functioned (in the 1960s) by varying the fulcrum of the cam follower and patented it (US Patent 3,641,988). GM patented its own VVL system in 1975 but encountered problems and later abandoned the project

Fiat's VVL system moved the fulcrum of the rocker arms to control the valve lift.

Alfa Romeo's "variatore di fase" is a form of VVT. Not VVL. Fiat's VVL technology went into Alfa Romeo cars. VTEC uses lockable rocker arms with dual profile camshafts.

Q: What other brands use VVL?

A: There are many forms of VVL. Only with slightly different working mechanisms and different names.

Porsche's VarioCam Plus

Here are some of them:

BMW: Valvetronic

Nissan - Nissan Ecology Oriented Variable Valve Lift and Timing

Toyota – VVTL-i

General Motors – Intake Valve Lift Control (IVLC)

Porsche – VarioCam Plus

Subaru – i-Active Valve Lift System (i-AVLS)

Mitsubishi - MIVEC

Proton - CPS

In summary, Honda was a pioneer with its VTEC technology. Not that it was the first to use VVL, but it was the first to combine lockable rocker arms and dual profile camshafts. While the technology is very simple, Variable Valve Lift (VVL) allows you to combine two engine characteristics into one engine and change it as the engine was running.

It is a very simple solution with significant results. Like it or not, VTEC deserves a spot in the automotive hall of fame.