Racing has always played a major role in the life of Aprilia. The relatively small factory in Noale started its adventure in the mid-1970s and quickly became a major competitor in motocross. Passionate (and wealthy) founder and owner Ivano Beggio then turned his attention to roadracing, where Aprilia dominated the 125cc and 250cc classes until last year, when the FIM outlawed two-stroke engines.
But the 125 and 250 classes were not enough for Beggio, who extended his challenge into the realm of Superbike, giving life to the RSV1000 built around a 1000cc Rotax 60-degree V-Twin. In the very capable hands of Troy Corser and Noriyuki Haga, the RSV1000 failed to achieve the top laurels only by inches.
The 1000cc four-stroke MotoGP class also looked very attractive to Beggio, who poured bushels of euros into the ill-fated Aprilia Cube project. The bike was powered by a three-cylinder engine designed by Claudio Lombardi, a former Ferrari technician hired to manage all Aprilia four-stroke racing programs. Not only did the 1000cc inline-Three MotoGP racer prove inconsistent, Aprilia’s racing activity was fragmented on too many fronts at the same time money was running low. That combination of negative factors finally led Beggio to sell all of his motorcycling operations—Aprilia and Moto Guzzi—to scooter giant Piaggio.
To replace the no-longer-competitive RSV1000 and give Aprilia a second chance to reach the top of the SBK class, Piaggio launched a new project. After the first round of preliminary evaluations, three engine configurations remained on the table. Surprisingly, despite the Aprilia Cube failure, Claudio Lombardi again came up with an “inline-Three” concept. But he also submitted a narrow-angle V-Four design, along with a more conventional inline-Four.
In the end, the V-Four came out on top by offering the best compromise. It had the potential to be narrower than both the inline-Three and Four, and much more compact, lengthwise, than the 90-degree V-Four that was proposed only as a theoretical comparison but never considered a viable option by Aprilia’s technical team.
In reality, a narrow V-Four would be more balanced than an inline-Three in both primary and secondary order; and though it would be less balanced than an inline-Four in primary order, a very small balancing shaft could cancel any resultant vibrations. A narrow V-Four also is slightly less balanced than an inline-Four in secondary order, but only by a negligible factor; besides, the perceived vibrations would not be any more disturbing than those of an inline-Four.
Another major advantage of the narrow-angle V-Four concept was that it could be harnessed in a frame dimensionally similar to that of the world-championship-winning Aprilia 250 GP racer. This was a very positive point on which to capitalize, since the Aprilia 250 was always regarded as the best-handling bike in its class.
Based on their experience with the RSV1000 V-Twin, the Aprilia technicians started with a 60-degree Vee angle, then enlarged it to 65 degrees for practical accessibility and the best configuration of the intake system’s variable-length velocity stacks. (As a side note, let me point out that all the legendary Ferrari V12s have had their Vee angle set at 65 degrees rather than the customary 60 degrees for such engines. Is there any meaning in that? Hard to say.)
The rest, as the saying goes, is history. Aprilia's narrow-angle V-Four demonstrated superb performance potential in all forms. The SBK racer delivered in excess of 220 horsepower, as well as absolute rationality in terms of overall dimensions and layout, giving life to a super-compact bike. To ride it, Aprilia hired its never-failing sweetheart, Max Biaggi, who won the SBK title in 2010. He had a less-positive 2011 season but currently is in this year's championship points lead. And Aprilia's V-Four now is even trying its hand in MotoGP, powering a couple of CRT racers ridden by Randy dePuniet and Aleix Espargaró.
Apparently, Aprilia’s chief of the Race Department, Luigi Dall’Igna, has got a lot more in reserve. According to credible rumors, there are modifications ready to push the V-Four’s output past 230 horsepower. Further evolution will take advantage of the standard 81mm bore rule established by the FIM, thus bumping the bore from 78mm to 81 and consequently cutting the stroke from 52.3mm down to 48.5 for larger valves and safe higher rpm.
Obviously, this Aprilia narrow-angle V-Four has a few more tricks up its (4) sleeves.
When the men of Aprilia’s R&D; Department opted for the narrow-angle V-Four layout, they knew what they were doing. The engine is extremely compact and no taller or longer than an inline-Four, but it is much narrower and shorter than a 90-degree V-Four. At 152 lb. dry, the RSV4 Factory engine does not offer a meaningful advantage over an inline-Four in terms of weight.
This top view shows why the Vee angle had to be stretched from the original 60-degree design to the 65-degree configuration: to make room for properly designed inlet velocity stacks and their variable-length system.
The lower half of the crankcase, minus oil sump, weighs 13.5 lb. The three supports of the crankshaft are integral with the rest of the aluminum casting, with no steel inserts to prevent possible distortions. Steel or cast-iron inserts are used in other highly regarded engines such as the celebrated Porsche Boxer Six.
The crankcase upper half, inclusive of cylinder blocks, weighs 21 lb. Sleeves are aluminum with Cermetal bore treatment by Italian specialists Tecnol. Given the 78mm bore, the cylinders’ center-to-center spacing of 93 mm leaves plenty of meat to enlarge displacement to 1.1 liter, or to obtain an 81mm bore (as allowed by FIM rulebook) with a 48.5mm stroke for an even bolder Aprilia attempt in CRT MotoGP.
The complete crankcase is short, compact and very strong. Note the oval rear engine mounts that allow adjustment of engine height to optimize alignment of the countershaft sprocket, swingarm pivot and rear sprocket for maximum traction on any given track.
The crankshaft has its throws set at 180 degrees. Starting in 2012, all crankshafts are finely polished to reduce “fluid” drag at high rpm. The bare crankshaft weighs 12.9 lb.
The dimensions of the crankshaft are yet another strong point of the RSV4 engine. The construction is massive, with 46mm main and 39mm crank journals that overlap by 16.35mm to create a substantial section of uninterrupted forged steel, forming an almost totally flex-free structure. The outer main bearings are wider and feature a central groove to speed and optimize oil distribution inside the oiling circuit. The engine uses a double oil pump, one serving the high-pressure circuit to the crank bearings, the other feeding the high-speed circuit that cools heads and pistons. All bearings are Clevite 112.
The balancing shaft that sits in front of the crankshaft looks diminutive and, in fact, weighs just 1.26 lb. The balancing shaft must turn at the same speed as the crankshaft, since it counters the primary imbalance, so it engages the outer gear at the end of the crank at a 1:1 ratio. The inner gear on the balancing shaft is part of the starter motor’s reduction train.
The connecting rods measure 112mm center-to-center and weigh just 0.784 lb. apiece. The rod bolts are very expensive, high-quality aircraft items.
Forged pistons weigh .436 lb. with rings. The pin is 17mm in diameter and weighs .114 lb. The piston top is not perfectly clean, due to the very deep valve pockets necessary, but not to the point of damaging the quality of combustion.
The inlet ports have a very efficient profile. The are almost perfectly downdraft, generating a strong tumble effect for a well-aimed turbulence that speeds up combustion. This increases the thermodynamic efficiency of a combustion chamber that already is very neatly profiled. Inlet valves are set at a 10-degree angle.
Exhaust ports are properly arched for a perfect scavenging capability, with no losses of effective port area as happens when ports are too sharply curved. Exhaust valves are set at a 12 degrees angle, yielding a very narrow total valve included angle of 22 degrees. This is a determinant factor in having a combustion chamber that sports a compact profile and a clean design for high thermodynamic efficiency.
Unlike MV Agusta and Ducati, Aprilia went valve shopping in Japan, not in the USA. Inlet valves are titanium, have a diameter of 32mm with 5mm stems and weigh .776 ounces. Exhaust valves are steel and 26mm in diameter with 5mm stems. Each weighs 1.128 oz.
Inverted-cup tappets are quite conventional. Rumor has it that one evolutionary step for the CRT engines might be a switch to finger-type cam followers.
Inlet (right) and exhaust camshaft, complete with the set of gears that transmit the rotation from the inlet cam (driven by the distribution chain) to the exhaust cam. To keep valvetrain noise down, the gear on the exhaust cam is split and spring-loaded.
The cam chains are Morse units by BorgWarner. A chain guide (bottom) and a hydraulically driven tensioner ensure lash-free operation for timing correctness. Aprilia can switch from chain to gear cam drive within the same layout.
A picture truly can be worth a thousand words, as this computerized image aptly illustrates. It shows the distribution of all the critical internal components and the symmetry achieved from one cylinder bank to the other by using the same castings. Note the complex reduction gear train through which the starter motor turns the crankshaft.
The engine breathes through 48mm Dell’Orto throttle bodies, with butterfly-valve actuation by computerized wire and electric actuation motors in response to twistgrip rotation. The whole integrated injection-ignition system is by Italian specialist Magneti Marelli.
The RSV4 uses a cassette-type six-speed gearbox that is compact but rugged. The complete transmission assembly, including the mounting flange—but not the oil-bath slipper clutch—weighs 17.46 lb.
This shows the “box” that Aprilia’s engineers worked with when designing the RSV4 engine. They imagined the ideal swingarm length, output-sprocket location, front-wheel suspension-travel allowance and maximum permissible engine height, then tried to stay within that box with all of the V-Four’s external dimensions.
This animation shows the velocity stacks in both their short and tall variable positions inside the airbox. The stacks are tallest at lower rpm and move to their shortest as the engine revs to its peak. That variable “tuning” helps the engine produce its best output throughout the entire rpm range.