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Deactivating lifters allow engine valves to remain closed cutting off air and fuel to four of eight cylinders
<p> Deactivating lifters allow engine valves to remain closed, cutting off air and fuel to four of eight cylinders.</p>

More Evidence Next Small-Block Remains OHV

Surely I wasn’t the only journalist attending a General Motors powertrain briefing in Detroit this week hoping to weasel some information about the fifth-generation small-block V-8 to be fitted under the hoods of the next Chevrolet Corvette and GM’s fullsize pickups and SUVs.

Oh, the questions to ask: Will the block and head be aluminum, or will certain versions continue to make do with a cast-iron block? Will the classic 2-valve configuration remain, or is a multi-valve architecture likely?

Most pressing, Could the next-generation small-block use overhead cams, or must it use pushrods, which were part of the original design that launched 57 years ago?

Insiders say pushrods are likely because they are essential to the small-block’s legacy. But on-the-record discussions about the next-gen V-8 are not to be had. The cross-town rivalries are so fierce in the big-truck and muscle-car markets, still dominated by Detroit metal, that the Ren Cen is treating small-block information as a matter of national security.

GM had confirmed previously the next small-block will use direct fuel injection. A year ago, a GM Powertrain executive told WardsAuto those injectors will employ solenoid actuators instead of more-expensive piezo-based units.

This week, one more morsel fell from the GM Powertrain lunchtable: The next small-block, when it arrives (likely) sometime next year, will use Active Fuel Management, which is GM’s marketing name for cylinder deactivation.

The fuel-saving technology cuts off the supply of air and fuel to four of the eight cylinders during light-load conditions, such as decelerating and steady-state cruising on the highway, and the four remaining active cylinders produce additional power to compensate for the loss of energy, until a heavy throttle input forces all eight cylinders into service.

The response time is 30 milliseconds, and the transition between the two modes is nearly imperceptible.

That the new small-block will integrate AFM is no surprise. GM first launched the technology in 2004 on MY ’05 vehicles, and since then 4.6 million V-8s in fullsize pickups, SUVs and muscle cars have burned less fuel as a result.

AFM is a no-cost option on 17 GM models representing 28% of its fleet of cars and trucks. Fuel-economy varies, but AFM can boost fuel economy up to 12% in cars such as the Camaro and up to 8% in trucks and SUVs.

Current engines integrating the technology are the 5.3L, 6.0L and 6.2L small-block V-8s. XFE versions of the Chevrolet Silverado and GMC Sierra are rated at 15/22 mpg (15.6-10.6 L/100 km) in city/highway driving.

Cylinder deactivation has been a viable concept for a century. GM archivists found the earliest car with the technology was the 1917 Enger V12, which let the driver shut down an entire bank of six cylinders with a lever in the cabin.

Later iterations were noisy and unreliable, including GM’s ignominious V-8-6-4, an engine that could run on eight, six or four cylinders, if it ran at all.

Modern electronics, which offer 75 times more computing power than just 15 years ago, enable today’s systems to function without the driver even knowing it.

Honda integrates cylinder deactivation on overhead-cam V-6s, and Audi this fall will begin selling the S8 luxury sport sedan with an all-new 520 hp 4.0L twin-turbo DOHC V-8 equipped with cylinder deactivation that boosts fuel economy some 10%.

But putting cylinder deactivation on OHC architectures is more expensive because it requires twice the number of deactivating lifters.

Which brings us back to the question of valve actuation for the next-generation small-block.

In their AFM presentation this week, GM powertrain engineers Mark Stabinsky and Jordan Lee say an OHV architecture is ideally suited for cylinder deactivation because the enabling hardware is compact and few additional parts are required.

And with 4.6 million units on the road, GM says the system is robust, durable and void of warranty headaches.

Read between the lines, and a reasonable person could assume the next small-block will have pushrods.

The powertrain world closely watches such things because GM has produced and sold more than 100 million small-blocks since the 1950s, and the legendary engine has been tweaked, tensioned, timed and torque-tested by generations of GM powertrain engineers.

In spring 2004, Chrysler actually beat GM to market with modern cylinder deactivation on the 5.7L OHV Hemi V-8. Originally branded as the Multi-Displacement System, Chrysler now refers to it as Fuel Saver Technology on the ’13 Ram 1500 pickup. The all-new Ram also integrates stop/start technology.

Without providing specifics, GM engineers promise improvements with the next AFM system, including an “expanded flyzone” when the engine is running in 4-cyl. mode.

The engineers also say the next-generation AFM will be compatible with stop/start technology, as is the current.

A laudable goal would be to allow a V-8 to idle in 4-cyl. mode, which makes perfect sense to environmentally minded non-engineers. But Lee says a V-8 would shake uncontrollably if it were to idle with only four active cylinders. Still, the potential fuel savings would be enormous.

Even without stop/start, Stabinsky refers to AFM as “gotta have” technology in GM’s efforts to meet future corporate average fuel economy mandates.

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