Aston Martin 'feels' the pain stuffing V12 into Vantage

  • 27-Jul-2009 12:36 EDT
Aston V12Vantage.JPG

Aston Martin engineers pushed the boundaries of their capability to successfully squeeze a V12 into the engine bay of the V8 Vantage.

­­­As a producer of high-performance cars and with a long pedigree as a sports and racecar maker, Aston Martin knows that "feel" is nec­essary for success. Some cars may have impressive performance figures, but when driven they do not feel particularly quick—their performance masked perhaps by very effective sound insulation and muted exhaust and inlet noise.

Some elements of feel can be regarded as emotion, but Aston Martin applies a formula to define what it terms a product’s PFI (Performa­nce Fee­l Index), and it has done so for its new 6.0-L V12 Vantage, an extensive development of the current 4.7-L V8 Vantage.

"Although feel is essentially subjective, it is possible to rationalize it as numbers," explained Paul Barritt, Chief Platform Manager, Vantage Line. "So we measure the rate of change of acceleration in each gear, take the peak value of that acceleration, apply a weighting factor, and come up with a number that gives us the basis for comparison with other models. In the case of the V12 Vantage, it is 4.8; that for the V8 vantage is 4.2. It doesn’t mean the V8 is inferior, but it does demonstrate the very impressive feel of the V12. It is by far the most dynamic car we’ve done in terms of that level of response, and a 0-100 km/h time of 4.2 s is the fastest of any of our production cars."

The V12 Vantage project began, as so many Astons do, with a concept that was created less than two years ago; the production program took only 12 months. The company originally had no plans to upgrade the V8 Vantage to a V12, but the temptation proved too much.

"The project has been full of engineering challenges, and we had to push our boundaries to achieve it," said Barritt. "The car has been designed to deliver a precision driving experience for the focused driver—a road car that is capable on the track but that is not a track car."

Mass, a killer of good dynamics, was one problem. The V12 powertrain has a mass of about 100 kg (220 lb) more than the V8, and a target was to offset this by at least 50% via mass savings in other areas. But the extra power, 380 kW (510 hp) at 6500 rpm compared to the V8’s 313 kW (420 hp) at 7300 rpm, and particularly torque, 570 N·m (420 lb·ft) at 5750 rpm, up from the V8’s 470 N·m (347 lb·ft) at 5000 rpm, far exceed any mass downside. As well as carbon ceramic brakes saving 15 kg (33 lb), mass reductions include use of lighter forged aluminum wheels saving 5 kg (11 lb), lightweight inner rear quarter panels, and optional lightweight seats saving 15 kg. Curb mass is 1680 kg (3704 lb) and its front/rear distribution 51:49.

Squeezing the 6.0-L all-alloy, quad-cam, front/midmounted V12 into the V8 Vantage engine bay without increasing the car’s external dimensions was, to put it mildly, not easy, and the internal front structure had to be extensively revised forward of the suspension towers. Space also had to be found for the brake cooling system and twin-air intake system.

Craig Jamieson, Vehicle Engineering Manager V12 Vantage, explained that the V12 unit is some 200 mm (7.9 in) longer than the V8. "So we had quite a problem," he said. "One issue was the relationship between the back of the engine and the bulkhead. We have built up extensive knowledge around that area for the V8 and other models, particularly with regard to radiated heat and its effect on components. We did not want to compromise that knowledge, so all the space we had to win was to be in front of the engine."

This involved moving forward the front main structure that links the two longitudinals (for stiffness and crashworthiness). To achieve this, the extrusions were extended, which was simple enough, but cast nodes are used to hold the extrusions together on the V8, and these had to be extensively redesigned to achieve space targets for the V12 as the throttle end of the intake manifold is hard up against one of them.

To move the structure further forward also involved the repositioning of the radiator, cooling pack, and condenser. In the V8, the unit is angled to attain underhood clearance, but for the V12 it needed to be vertical, creating a height issue because under it is the structure and cooling ducts for the brakes. "It was a fight for every mm," said Barritt.

But the team of a dozen engineers took an optimistic view and spent hundreds of hours studying CAD images to achieve a solution. Another problem was the relationship between the steering rack and the engine because it protruded into the area of the V12’s oil sump.

The V8 has a dry sump, but the V12 had to have a wet sump because there was insufficient space for an associated oil tank. However, the wet sump had to be engineered to meet Aston’s durability requirements. Testing included 8000 km (4970 mi) at the Nürburgring to ensure that the sump could cope with high-g cornering and, even more importantly, braking.

"In fact, oil handling and the associated system proved the main engineering challenge of getting the engine into the car," said Jamieson. "But it was met—as were all standard Aston Martin quality and durability requirements."

Having a small team on the project helped, he said, because engineers could be zone (or small system) rather than just component focused. "Much credit goes to our engineers who developed a wet sump on such a long engine without oil surge or oil-handling issues."

The lowest part of the engine and its associated systems is the radiator, having 105 mm (4.1 in) of ground clearance, 15 mm (0.6 in) less than that of the V8. "But it was necessary to get the radiator pack under the hood and also get the cooling duct cross-sectional area we needed," stated Jamieson. "The lessons we learned from such a challenging packaging exercise, and the robustness required to question all clearances, will certainly be used on future models."

The engine also includes a "Sport" button (or "Fun" button, said Paul Barritt), providing two powertrain modes, Normal and Sport, the latter changing throttle progression mapping and operating the car’s semi-active exhaust system to reduce back pressure and enhance exhaust sound, another aspect that adds to the car’s feel.

Although the engine is very similar to that of the DB9, it has a bypass engine air intake port that opens at 5500 rpm, revised induction system, and reprofiled inlet ports. Its six-speed manual gearbox is rear-mounted. An alloy torque tube and carbon-fiber propshaft are fitted. Final drive ratio is 3.71:1 (compared to the V8’s 3.909:1) to better use available torque.

The V12's carbon ceramic matrix brakes are by Brembo; Barritt envisages all Astons having carbon ceramic brakes in the future.

And with the successful experience gained in packaging the V12 in a V8 engine bay, he might also envisage Aston’s Performance Feel Index moving up a notch or two as new models emerge.­­

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