Technical Analysis: 90º V4 Engine By Kevin Camero

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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 cg 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 Vee 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 Vee engines, both in SBK, where they are Twins, and in MotoGP, where they are V-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 1/2 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 cg to move forward, allowing 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 shock news that Honda is winning races with the very same 90-degree Vee 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 possibly be. The outside diameter of the con-rod’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 R&D dollars wouldn’t hurt, either. MotoGP is not a contest of equals.
 
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Doesn't remind me of a Ducati. Reminds me of an Interceptor. By the time Ducati made a V4 (Desmosedici), Honda had been making one for 20 years. Yamaha for nearly as long. Suzuki's had already come and gone. The engine angle is tilted back a bit. Seems counterintuitive to keeping the front tire loaded but I guess you can move the entire engine forward in the frame that way. shrug I can say from experience that if you go from Ninja (ZX600C) to Magna (VF700C), the Magna's front end feels spooky. It doesn't really low side you into a faceplant but it doesn't feel planted.
 

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Originally Posted By: Spazdog
The engine angle is tilted back a bit. Seems counterintuitive to keeping the front tire loaded but I guess you can move the entire engine forward in the frame that way. shrug I can say from experience that if you go from Ninja (ZX600C) to Magna (VF700C), the Magna's front end feels spooky. It doesn't really low side you into a faceplant but it doesn't feel planted.
Moving the engine as far forward as possible is a design goal... I can't speak for Maggy but my V4 front feels planted... Quote Nicky Hayden... "It's awesome. the RC45 is so stable and it's so easy to feel the front." Quote Performance Bikes... "Confidence is a big chuck of what makes the RC45 excellent. It feels so super glued to the road it'd take a full time Gorilla on the gas to fatally unstick it. and the RC45 gives that confidence without asking-on the others you have to go looking for it. For a homologated racer on the road, the RC45 is incredibly civilized"
 
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Originally Posted By: Spazdog
By the time Ducati made a V4 (Desmosedici), Honda had been making one for 20 years. Yamaha for nearly as long. Suzuki's had already come and gone.
FWIW, Ducati made a V4 motorcycle engine in the early 60's. The bike with that engine proved to be too powerful for the tires of the period. It was seriously detuned, so tires would last, but at that point the added complexity and potential power of a V4 that couldn't be utilized, became superfluous. So it didn't go into regular production.
 
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Looks like an old Intercepter/Magna/Sabre engine. I would not say my Magna is spooky, but the front end certainly feels lighter than my KZ. It is a shame V-4's never really caught on with street bikes, they feel like they have the high end of a inline 4 with more low end torque. I guess people got burned by Honda's cam issues.
 

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Originally Posted By: THE_TROTS
Looks like an old Intercepter/Magna/Sabre engine. I would not say my Magna is spooky, but the front end certainly feels lighter than my KZ. It is a shame V-4's never really caught on with street bikes, they feel like they have the high end of a inline 4 with more low end torque. I guess people got burned by Honda's cam issues.
Yamaha had a pretty successful go with the V-MAX and its V4 at least....
 
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Honda is already using v4s in the 800 and 1200 range of street bikes (VFR variants, shaft in the 1200 and chain in the 800) and did so from 1990 to recently in the ST1100 and ST1200 (although these were longitudinal in the frame) Cost of production has always been cited as an issue.
 

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Originally Posted By: THE_TROTS
It is a shame V-4's never really caught on with street bikes, they feel like they have the high end of a inline 4 with more low end torque. I guess people got burned by Honda's cam issues.
The desire is there but cost is the main hurdle for most consumer because I4s are cheap to manufacture compared to V4s which are expensive like V2s to produce... The great camshaft crisis in 84 about off killed enthusiasm for the VF... as you know every stop gap measure was tried in curing the problem but the real culprit was Honda's short cut in machining steps of the cam bearing blocks... they dropped the line bore step and machined the cam bearing blocks separately... this resulted in mix match of clearances... in short the cams flopped about... hard coat damage soon followed... For a cure Honda... in 86... went back to the more accurate and expensive method of line boring the cam bearing blocks... You can note the external difference in the head design... the 84's & 85's rubber valve cover gasket is flat... whereas the 86's rubber valve cover gasket is half circled covering where it was line bored... Honda was typically silent for a long time and this led to all sorts of home cures including better top oiling kits... shorten oil change intervals... larger gapped valve clearances... installing new cam tensioners... auxiliary cooling fans kits... etc etc etc... but none of these address the root cause... Only after Honda took a lot of stick did they finally go back to the timely process of line boring the cam bearing blocks on the head so the tolerances complimented each other...
 
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