GM Reveals Small-Block V-8 with Direct Injection - wardsauto.com
By Mike Sutton
Aug. 29, 2007
MILFORD, MI Although General Motors Corp. is dividing its resources to cover all fronts of advanced powertrain development, the future of the auto makers foundation OHV small-block V-8 architecture appears secure with the advent of direct-injection gasoline (DIG) technology.
Among the various exhibits of engineering bravado on display at the auto makers proving grounds here, including two-mode hybrid-electric drivetrains, ultra-clean turbodiesels and homogeneous charge compression ignition flex-fuel engines, a seemingly untouched Cadillac Escalade stands out.
Emblazoned with giant E85 banners down its flanks, there is little to indicate the industrys first OHV V-8 with DIG fueling lurks beneath the SUVs pearl white hood.
The experimental engine is based on GMs current all-aluminum Gen IV 6.2L V-8 (L92) found in the Escalade, GMC Yukon Denali and Hummer H2. Depending on the application, the powerplant, which sports port fuel injection, variable valve timing (VVT) and dual-cam phasing, is rated between 380-403 hp in stock form.
However, with a little tweaking to accommodate the auto industrys latest fuel-injection hardware, the prototype V-8 is producing well north of 450 hp (on gasoline), says Dave Sczomak, development engineer-GM Powertrain Advanced Engineering.
Running the engine on E85 ethanol allows for even more power to be coaxed from the big V-8, he adds, noting the 85%/15% ethanol/gasoline mix generally carries a race fuel-like 106 octane rating.
Cruising the web of test roads onsite, the Escalade motors along smoothly with a characteristic large-displacement V-8 burble. However, mashing the gas from a standstill produces a wave of power that propels the big truck at a noticeably more rapid pace than the production version.
Along with the substantial increase in horsepower, DIG also contributes to about a 10% increase in low-end torque, Sczomak says. In addition, fuel economy is moderately improved (3-6%), as are cold-start emissions of hydrocarbons.
To accommodate the DIG fueling system, GM redesigned the L92 cylinder heads, rearranging the intake ports to make room for the eight high-pressure injectors that squirt fuel directly into the side of the combustion chamber at 2,250 psi (155 bar).
New dished pistons similar to a diesels were installed for added clearance of the injectors. They also contribute to a greater compression ratio (11.5:1 vs. 10.5:1), which can be employed because of the high-octane composition of E85 and the knock-reducing cooling effect of introducing fuel directly into the cylinder.
A modified engine controller manages the engines operation, while VVT and Active Fuel Management cylinder deactivation contribute to efficiency and refinement.
The development sounds like a no-brainer for improving nearly every aspect of the near-60-year-old small blocks performance.
However, Tom Stephens, group vice president-GM Powertrain and Quality, notes introducing a production DIG small block would require the next-generation architecture of the engine, or Gen V.
This primarily is due to the huge volumes of V-8 engines GM produces, Sczomak says, noting a radical change in cylinder-head design, for example, becomes a monumental undertaking when taking into account GMs annual build of more than 1 million small block V-8s.
Fortunately, timing is on the auto makers side. The recent introduction of the 08 Corvettes 430-hp LS3 V-8, along with the release later this year of the 08 Chevrolet Tahoe Hybrids 6.0L V-8, represent the last editions of the Gen IV engine family, Stephens says.
All subsequent introductions will be of the Gen V architecture and could have DIG fueling integrated from the ground up, especially considering the refinement of the current test engines operation. The greater specific output provided by DIG also would allow for greater engine downsizing, thereby improving fuel economy even further.
GM would want to introduce this (DIG) on a high-profile vehicle, such as the new (Chevrolet) Camaro or (rear-wheel-drive) Impala, Global Insight analyst John Wolkonowicz says, referring to the auto makers plans for new volume models based on its global RWD platform developed by GM Holden Ltd. in Australia.
The new Camaro, which originally was shown at the 2005 North American International Auto Show in Detroit, is expected to appear later next year as an 09 model, with the all-new RWD Impala taking form sometime early in the next decade. Revisions for future generations of the Corvette and Chevrolet Silverado/GMC Sierra pickups are expected in the same timeframe, Wolkonowicz says.
By capitalizing on areas of significant improvement that remain untapped in its core engine lineup, while simultaneously amping up the arrival of its new hybrid-electric vehicles, clean diesels and hydrogen fuel cells, GM clearly is betting on an ever-fracturing market for advanced powertrains.
As a result, the iconic grumble of the small-block V-8 appears poised to remain a fixture of the automotive landscape for the foreseeable future.
