Aprilia V4 - Multi-Cylinder Engine

This CAD illustration of the Aprilia engine shows the narrow build of the V-4, which the company claims is no wider than its current 998cc V-twin

Aprilia V-4 Engine Unveiled
The recently rescued Italian firm enters the multicylinder world with an all-new four-cylinder destined to power a new superbike

First Look
Long known for its lineup of innovative sportbikes built upon the company's signature 60-degree V-twin, Aprilia's return in '08 to the superbike wars-both in competition and on the showroom floor-will be anchored by its all-new 999cc V-4 engine unveiled at the Milan Show. Designed entirely in-house at Aprilia's R&D works, the new engine is claimed to produce more than 210 horsepower in race trim and boasts some unique engineering features that allow for a much more narrow and compact design than previous V-4 engines.

Although the company adspeak boasts that the engine went from "general layout to assembly of the first prototypes and engine start-up for initial bench testing" in "a few months," it's been known that Aprilia has been secretly developing this engine for quite some time. However, the company's recent financial problems and the ensuing buyout two years ago by Italian business magnate Roberto Colaninno's Piaggio Group caused the project to be shelved until the finances to continue development became available. With an infusion of cash from the Piaggio Group, Aprilia's engineers were finally able to finish the project, which is hoped will help revive the company's competitive reputation in the wake of its past monetary woes.

Aprilia reps reiterate that the new Race Machine V-4 is not intended to replace the company's long-standing V-twin engine nor the RSV Mille sportbikes powered by the V-twin. Current plans are for an expensive limited-production homologation model to be unveiled for '08, in anticipation of a return to World Superbike competition the same year.

Choosing a 65-degree vee angle allowed Aprilia engineers to keep the engine's overall length in check, permitting more leeway with engine placement in the chassis for optimum handling

In order to keep the new engine as compact as possible, Aprilia engineers settled on a 65-degree vee angle for the four-cylinder. By staying close to the 60-degree angle of the V-twin, Aprilia can use much of its current chassis data without having to spend the time and money designing a completely new chassis around a larger powerplant. The narrow vee configuration's short length helps keep the wheelbase short and permits a longer swingarm design for better weight distribution. On the other hand, a narrow angle restricts designing an optimum intake port and airbox, so opening up the vee as much as possible was necessary. A secondary counterbalance shaft, which robs power, was also required to keep primary balance in check.

Although bore and stroke figures weren't revealed, the engine is definitely very oversquare, with the stated 13,500-rpm redline surely being on the conservative side. Like the old Honda V-4s, the cylinders are cast into the upper case half, with integrated liners for maximum rigidity. Forged slipper-skirt pistons force a fairly high (for a liter-size engine) 12.5:1 compression ratio.

Probably the most unique aspect of the new Aprilia engine is the hybrid chain/gear camshaft drive. Normal DOHC cylinder heads require a lot of metal to support both the camshafts and camshaft drive, adding substantial weight and overall width to the assembly. The Aprilia uses a normal side-mounted chain drive for the intake cam, but instead of the chain also transmitting power to the exhaust cam, a pair of gears running off the intake cam between the cylinders drives the exhaust cam. This results in cylinder heads that are even more compact than the heads on the V60 Magnesium V-twin engine currently in use on the RSV Mille, and it also extends cam chain life. Both intake and exhaust valves are titanium.

The transmission is a fully removable cassette assembly, with Aprilia's trademark pneumatically actuated slipper clutch preventing wheel hop during hard braking. Unlike the V60 twin, however, the V-4 utilizes a conventional wet-sump lubrication system, instead of the twin's dry-sump unit.

Aprilia's unique hybrid chain/gear camshaft drive, which runs the exhaust cam via gears off the intake cam, allows for very compact cylinder heads. Fuel injection is controlled by the latest ride-by-wire Magneti Marelli EMS system, which controls both pairs of throttle bodies separately

Fueling is handled by the latest-generation Magneti Marelli engine-management system, which follows along with the most recent MotoGP engine-control developments, including full ride-by-wire throttle actuation. As with many of the latest MotoGP racebikes, each pair of cylinders' throttle plates have a dedicated servo motor controlled separately by the EMS, permitting independent operation between the two pairs and allowing for increased flexibility in power output; even real-time traction control was mentioned in connection with the new Marelli EMS. Each throttle body carries two injectors, one just downstream from the throttle plate and the other a shower-type injector situated in the roof of the airbox above each intake funnel.

Spy photos of a prototype engine being track-tested in a modified RSV Mille chassis in Europe have already surfaced. Reports from overseas say the engine has already passed strenuous bench testing and that the finished production model will be unveiled at the Milan Show this winter.