GT-R Motor News from Mitch B

One reason is that while screaming high-rpm engine performance may excite enthusiasts and provide a thrill on race tracks, the narrow, high-rpm powerband that is acceptable for racing can provide an unsatisfactory experience in street driving.

Traffic, weather, and variable driver skill can all conspire to make many racing-derived engines disappointing to retail customers. Although Nissan touts the racing contribution to its new VR38 engine seen in the company’s new GT-R supercar, the company emphasizes that a driver-friendly powerband is a key attribute.

“More important than the absolute power is the manner in which it is delivered,” said Mizuno. “The engine’s very tractable, and that means it’s very easy to drive—a key quality of the Nissan GT-R.” Peak torque of 434 lb•ft (588 N•m) is available from 3200 rpm, he pointed out.

That compares to a 5200-rpm torque peak for the company’s well-liked VQ V6 as applied to the Infiniti G37 coupe. Peak power of 473 hp (353 kW) also occurs at lower revs—6400 rpm for the VR compared to 7000 rpm for the VQ.

Despite the obvious similarities between the engines, including the 95.5-mm (3.76-in) bore diameter, there are dramatic differences between them— all the way down to the VR’s closed-deck block, which provides a stronger foundation and better head gasket sealing than the VQ’s open-deck design. Gasket integrity is a key concern in turbocharged engines, remarked Colin Price, Product Planning Manager for Nissan North America.

The engines differ in their stroke, with the VR’s longer 88.4 mm (3.48 in) yielding the added displacement. The VR’s compression ratio is reduced to 9.0:1 from the VQ’s 11.0:1. Because Mizuno and his hand-picked team came from Nissan’s racing organization, secrecy evidently remains a prime consideration, even following the GT-R’s launch. As a result, details such as boost pressure have not been made available.

A significant feature of the VR’s aluminum block is the use of a sprayed plasma coating in the cylinder bores without any cast iron sleeves installed. This 0.15-mm (0.006-in) thick layer substitutes for a 2.6-mm (0.10-in) iron liner, which not only reduces the engine’s mass by 2.8 kg (5.2 lb), but also increases the potential bore diameter by 4.8 mm (0.19 in) on the same bore centers.

The implication, therefore, is that the VR has a potential displacement of 4190 cm3. That 10% increase in displacement suggests, then, that the potential larger engine would have a projected output of about 520 hp (388 kW) and 477 lb•ft (647 N•m).

The thinner cylinder walls improve heat transfer from the combustion chamber to the coolant passages, reducing the temperature between cylinders by 40°C (72°F), the company stated. Heat control is critical for the engine to survive with the thin plasma layers in its cylinders. To further aid in those cylinders’ durability, Nissan has devised a sophisticated oil system that combines some of the traits of a conventional wet-sump system with those of a racing-style dry sump.

The oil return lines that drain from the heads extend across the pan to the other side of the engine so that in high-g corner maneuvers, oil in the pan is not pushed back up into the cylinder head. A dedicated scavenging pump evacuates oil from the dual IHI-supplied turbochargers’ shafts to prevent buildup in those areas. The measures ensure that the engine can withstand as much as 1.5 lateral g, according to Price. The company specifies ExxonMobil’s Mobil1 0W-40 synthetic oil exclusively.

Dan Carney