VARIABLE CAM TIMING: The Best of Both Worlds

Many car engines have had variable valve timing (VVT) for years, as it is a leading tool in the effort to replace less fuel-efficient larger engines with more compact ones.

There are two basic valve-timing personalities. One is the “Harley,” which pulls strongly from low rpm but runs out of breath as it revs. The other is the “GSX-R,” which pays for the high horsepower it delivers at higher revs by being decidedly limp-wristed below 6,000 rpm. Each personality has its enthusiasts.

For years, it was assumed the two groups of riders were separate, each satisfied with what it had.

Then Ducati built the Diavel, which, with only 11 degrees of valve overlap, pulled like a John Deere. Riders loved it because a slight rotation of the right wrist (and 96 pound-feet of peak torque) sent it thundering forward. Just like a Harley.

Yet even as de-tuned as it was, the Diavel still delivered 96 more peak horsepower than a you-know-what. Excitement. That is a unique combination, and this Ducati sold well among those who already owned Harleys but wondered what more motorcycling could offer in a V-twin.

This discovery supplied a reason to experiment further. Giving the Diavel only 11 degrees of valve overlap cost it a bunch of peak power, but with VVT a lot of that could be recovered. Ducati’s Desmodromic Variable Timing system (DVT) uses the same kind of hydraulic cam phase changers found on automotive engines to constantly optimize valve timing for the rpm the engine is turning. The result merges the two valve-timing personalities into one with both kinds of strengths in the current 1198 Testastretta engine.

Why hasn’t this happened sooner? The Japanese manufacturers ran focus group tests years ago, which discovered that most riders prefer engines with high rideability, with wider, more usable power. But I suspect VVT failed to spread beyond a couple of applications because it added cost in price-competitive markets.

Ducati operates in a different market, one in which buyers explore because they are seeking something unusual. If the increased parts count and R&D of variable valve timing add to the price, such buyers are not discouraged. Who knows? Europe has led the way in adopting electronics on motorcycles. Will variable valve timing similarly take root and thrive?