GENEVA - Nearly 20 years ago, the short-lived Cadillac 8-6-4 engine gave General Motors an embarrassing black eye.
Now GM is looking to bring back a version of that engine.
Fritz Indra, executive director of advanced engineering for GM Powertrain Group, believes cylinder deactivation, the technology behind the old 8-6-4, is the simplest and least expensive way to improve fuel economy.
The 8-6-4, a 6.0-liter V-8 introduced in 1981, was unreliable. Its cylinder deactivation system, supplied by Eaton Corp., was hamstrung by the era's rudimentary electronics. Cadillac deleted the engine from all models except limousines in 1982.
Indra says GM can solve the 8-6-4's problems with new electronics. The result is an engine that can move seamlessly from working on all eight cylinders to working on just four. Indra estimates the technology will increase an engine's fuel economy up to 18 percent.
The new GM engine does not have a 6-cylinder mode, like the 8-6-4 did.
'I'm still convinced this is the right way to go,' Indra said. 'Especially with (GM's) overhead-valve pushrod (engines), cylinder deactivation is ideal. It's so simple. And there (are) more benefits than all the other technologies.
'We are predicting a renaissance for this engine design.'
Indra said GM could have a production version of the engine within two to three years.
GM is testing cylinder deactivation with the Chevrolet Corvette's 5.7-liter small-block V-8. With the Corvette, the benefits could be an increase in fuel economy of up to 18 percent, Indra said.
The goal, he said at the Geneva International Motor Show, is to run the Corvette from Detroit to Michigan's Mackinac Island, about 300 miles, on four cylinders without the driver noticing a difference.
Other automakers have looked at cylinder deactivation. DaimlerChrysler already offers 'cylinder cut-out' in Europe on the 5.0-liter V-8 engine that powers its Mercedes-Benz S class. DaimlerChrysler will introduce a new cylinder deactivation V-12 engine for the 2001 model year in Europe.
The Vienna-born Indra held a top powertrain job at Audi AG before joining GM's Adam Opel AG subsidiary in 1985.
A respected expert, his confidence in cylinder deactivation is based on significant improvements in electronic engine management systems. Those improvements make it possible to switch an engine from eight cylinders to four without the driver noticing a difference.
Indra said cylinder deactivation is easier to adapt to GM's two-valve pushrod engines than more complicated overhead-cam engines. 'You only have two valves to close' per cylinder, he said.
RUNNING ON 4
The engine uses hydraulics to deactivate the cylinders instead of the noisier electromagnetic system used in the old 8-6-4 engine, according to Indra.
Indra estimates the engine could run on four cylinders up to 90 percent of the time, and then kick in all eight cylinders in higher load situations.
'Our goal here is that the customer should never feel whether it's running on four or eight,' he said.
'Only if you are overtaking another car or (carrying) a heavy load, then you need eight cylinders.'
When the engine shuts down four of its cylinders, it closes the valves on those cylinders. By doing that, GM is able to keep pressure and the gases hot in those pistons.
The fuel economy results are similar to those of direct injection, Indra said.
With direct injection, fuel is sprayed directly into the cylinder to better tailor the mixture for emissions and fuel economy. But direct injection requires catalytic converters that can remove the higher amounts of oxides of nitrogen exhausted by lean-burn direct-injection engines. Those converters are easily contaminated by the high amounts of sulfur found in North American gasoline.
With cylinder deactivation, 'you are not relying on sulfur-free fuel, so you can use the fuel as it is, you can use the catalytic converters as they are today,' Indra said.
More testing needed
Indra said GM has test cars equipped with the cylinder-deactivation engines, but they need to go through summer and winter testing before GM commits to production.
Said Indra: 'For me, this is by far the best technology we have currently.'
Staff Reporter Aaron Robinson contributed to this report