Technical Update Honda's Big Surprise

TECHNICAL UPDATE 

HONDA'S BIG SURPRISE

IGNITION

NEWS

How Honda outwitted Ducati at the V-Four packaging game

Kevin Cameron

HAVE A LOOK AT THIS engine cross-section line drawing. It purports to be a patent drawing of a “super streetbike” that Honda will build as a homologation special for the FIM Superbike World Championship. And it is said to be closely related to the production racer Honda plans to offer for sale to race teams for the 2014 MotoGP season. As you can see, this is a 90-degree V-Four. The front cylinders’ axis is 35 degrees above horizontal. Remind you of a Ducati? Why, yes! For two

years, some have been saying that Ducati’s problems in MotoGP come from the excessive bulk of its 90-degree V-Four, pushing the engine’s eg so far back from the front wheel that there’s not enough load on the front to keep the tire hot. But wait! Recently, Honda arranged an impromptu “photo op” in which its highly successful and series-leading RC213V engine was seen to also have a 90-degree V angle. Revelation! Honda has a historic commitment to V-Fours, having pioneered

the super-radical, but never successful, oval-piston NR500 in the late 1970s then spun off a long series of V-Four street and racebikes, including the VFRs, RC30 and RC45. Why? Because its engineers did not like the inherent vibration and crankcase flexure of inline-Fours. They should know: Honda won many GP championships in the 1960s with air-cooled inline-Fours, despite their problems. What are the V-Four’s advantages? First, a 90-degree Vee engine can easily be given perfect primary balance without resorting to balance shafts. Second, a compact V-Four centralizes mass very well, as it is the engine closest to being a cannonball. In your mind, compare the ease of turning corners carrying a) a 12-foot ladder weighing 24 pounds or b) a 24-pound cannonball.

Ducati also has long experience with 90-degree V engines, both in SBK, where they are Twins, and in MotoGP, where they are Fours. The front cylinder of Ducati’s original, early 1970s V-Twin was only 15 degrees above the horizontal so that long cylinder pushed the heavy crank and crankcase rearward, giving that bike its long 60-inch wheelbase and very low front-tire loading. To get stability with so little weight on the front, Ducati resorted to a 31-degree steering rake angle and 4.5 inches of trail. Result? Very slow and rather heavy steering.

Since then, Ducati has progressively raised the angle of the front cylinder to allow the engine’s eg to move forward, permitting shorter wheelbases and somewhat less conservative steering geometry, but the problem is not solved, only reduced. Every manufacturer picks a set of compromises and works with it.

Now comes the shocking news that Honda is winning races with the very same 90-degree V angle. How can this be? The drawing shows at least three methods Honda has used to make its engine more compact, so it can be moved forward enough to produce good performance, even on the spec Bridgestone tires that have been such a problem for Ducati:

1) This engine has short connecting rods. Whereas Formula 1 racing engines have a 2.5 rod ratio (center-to-center length divided by stroke) and conventional race engines lie between 2.0 and 2.2, this engine has a 1.8 ratio. One year at Daytona, John Britten reached into his pocket and pulled out a titanium rod. “Cosworth is using

a 1.8 rod ratio, so that was good enough for me,” he said.

2) The wristpins in this engine’s extremely short pistons are as high in the piston as they can be.

The outside diameter of the conrod’s small end barely clears the underside of the piston crown.

3) By making the exhaust valves shorter than the intakes, the cam cover can be angled to give more cylinder-head-to-front tire clearance on the exhaust side (Ducati has also used this technique). Why not shorten both? Long intake-valve stems allow the use of high-flowing, nearly straight ports. These are not as essential on the exhaust side.

Yes, but maybe Ducati has already done all these things, right? Maybe not. Think of how factory rider Andrea Dovizioso has recently qualified a lot higher than he has finished. When I asked Ducati MotoGP Project Manager Paolo Ciabatti about this, he said it is because “our bike is quite physical to ride.” That is, it takes a lot of muscle to heave it around. One or two fast laps in qualifying are no problem, but 24 to 30 laps of racing are exhausting. This suggests the Ducati still has the slower steering geometry required to compensate for less-than-optimal weight on the front tire.

Another point is that we know Ducati’s general philosophy is to make all the power that engineering can stuff into the engine then use electronics to make it rideable.

Short rods are not preferred for the highest power (greater rod angularity pushes the pistons harder against the cylinder walls, generating extra friction), and Ducati already has experience with the heat problem of high wristpin location, causing lube breakdown and metal pickup on the pin.

Okay, maybe I’m building castles in the air, but the drawing is suggestive. And the Ducatis are a second-a-lap slow. If Honda can do it, Ducati, whose engineers are just as intelligent and well educated, should be able to do it, too. To add an element of crudity to the discussion, an extra $30 million in R&D money wouldn’t hurt, either. MotoGP is not a contest of equals. ETU

A COMPACT V-FOUR CENTRALIZES MASS VERY WELL, AS IT IS THE ENGINE CLOSEST TO BEING A CANNONBALL.