Power of 3

In one of the most significant redesigns in the 50-plus-year history of its “small-block” V-8 engine architecture, General Motors Corp. powertrain engineers are developing a new 3-valve-per-cylinder layout for GM's overhead-valve V-8 and V-6 engines.

The new 3-valve design is meant to enhance the performance of the OHV V-6 and V-8 engines — currently using 2-valve-per-cylinder layouts — that GM prefers to the overhead-camshaft engines often favored by Japanese and European auto makers. GM Powertrain builds millions of the current OHV V-6/V-8 2-valve engines.

That group includes the legendary small-block V-8, which GM installs in everything from Chevrolet Silverado to Cadillac CTS.

GM Powertrain sources will not say when the 3-valve engines will be in production. And although Alan Hayman, manager-advanced concept group in GM Powertrain's Advanced Powertrain unit, will not confirm a production-vehicle launch date for the new engine design, he says launch of the 3-valve architecture would come after the so-called “Gen IV” version of the small-block V-8 is introduced some time next year.

For V-6s, sources say the 3-valve architecture — which employs a unique “transfer pushrod and transfer arm” to activate the exhaust valve — could add 10% to 15% more power with no impact on fuel economy.

A new cylinder head design employs the transfer arm and pushrod to locate the exhaust valve across the head from the dual intake valves. The new layout also repositions the sparkplug to a central location between the intake and exhaust valves.

“We're doing it for performance,” Hayman says. “The customer is asking for more performance without a cost increase.”

Hayman says a V-6 generating 240 hp, for example, could produce 270 hp by using the 3-valve cylinder head — yet the cost increase would be marginal. “A lot cheaper than an overhead-cam 3-valve,” says Hayman, in apparent reference to Ford Motor Co.'s new-for-'04 3-valve design for its Triton V-8 engine family.

He says GM's new 3-valve design is perfectly suited to fulfill the low-cost priority. The layout “requires minimal tearup to the (engine) lower end,” a critical factor in curbing the need for costly new components or castings.

The cost saving in relation to the new performance netted by the 3-valve design is significant. Hayman says that for a 2-valve V-6, adopting the 3-valve cylinder head is about one-third the cost of going to an overhead-cam/4-valve-per-cylinder layout. “We're excited about that,” he says.

Equally important, the 3-valve design is fully compatible with Displacement on Demand, or DOD, the cylinder-deactivation technology GM Powertrain will begin this year to widely deploy to enhance the fuel economy of its overhead-valve V-8 and V-6 engines.

Hayman says because changes for the new engine design are limited almost exclusively to the cylinder head itself, 2-valve and 3-valve variants can run down the same production lines, and “there are only three or four machining differences.”

Hayman says the 3-valve variants likely would be “upgrade” engines, particularly in the case of the V-6s. The 3-valve engines also might be used to differentiate between brands, with the higher-performance 3-valve version of a V-6 going to Pontiac, for instance, underscoring that division's performance image.

Because of the “integral” design, there are no packaging constraints, he adds: The 3-valve V-6s and V-8s could be fitted in any vehicle that uses the 2-valve counterpart.

“I would think we'd always keep the 2-valve (design) as long as it meets the requirement of the market. We'll consider what the marketplace is asking for.”

Hayman agrees the move to a 3-valve layout is a significant step for the beloved small-block V-8 that dates to 1955. “It's as significant as going from Gen II to Gen III.”

But the 5-decade-old small-block's 2-valve design, he insists, still holds room for improvement.

“The 3-valve is a way in the future,” Hayman says. “There are some surprises in store for the 2-valve (small-block V-8). And we're not talking about 10 or 15 hp. Our goal is to remain the leader in truck powertrains.”