MOTIONCARS Magazine
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Technical Analysis

VTEC.  VVT-i.  VANOS.  VarioCam.   These are acronyms that you will have seen in various car ads, all denoting variable valve timing.  What is variable valve timing?  Is it something truly worth having, or is it just as effective as a sporty sticker on your car: it makes you feel like you’re going faster, but doesn’t really do anything? 

Well, let us tell you now that variable valve timing is a genuine technological improvement for the internal-combustion engine, boosting both fuel efficiency and power output.  

A couple of basic terms: torque is the pulling power that your engine is capable of.  If you hold a 1 kg weight 1 meter away from your body (assuming your arm can extend that long), your arm will feel a force of 1 kg-meter, or about 10 Newton-meters (Nm).  Power is that force applied over a certain time.  Spin an engine with 10 Nm at 1000 rpm, and you’ll generate about 14 bhp (10.4 kilowatts) of power.  The faster you spin an engine, the more power it generates.  That’s how the same 3.0-liter displacement can generate 155 bhp at 4000 rpm in a Hyundai road car engine, and almost 900 bhp at 19000 rpm in a Ferrari Formula One powerplant.  Now some of us would love to be driving around with engines peaking at 19000 rpm, but it’s not practical: we’d all have to be shifting like crazy, cars would be screaming all the time, and we’d need to refuel every 100 laps, er, km.

For the sake of fuel efficiency, modern engines tend to have smaller displacements.  They can be made to generate the same power as larger, older engines by revving them higher.    However, the wide rev capability creates the problem of which part of the rev range to optimize the valve timing for.  A mild or nearly round cam profile is ideal for the lower revs; it creates a low, wide torque band with good emissions and smooth idle.  Such an engine has good initial acceleration but runs out of breath at higher revs.  If you've driven a Lite-Ace, you know how this feels.