Pushrods in Perpetuity

Don Sherman

Will pushrod engines last forever? Probably not, but in April, General Motors announced that it's investing $890 million in a new, fifth-generation small-block V-8. Although the announcement didn't state that pushrod-operated valves are part of the deal, you can take that assumption to the bank.

GM did say that all of the fifth-generation engines will have aluminum blocks, a feature that's common but not universal in today's fourth-generation V-8 applications. In addition, direct fuel injection will be standard, along with E85 fueling capability and an "all-new advanced combustion system."

The common threads through the first four small-block generations are a 4.4-inch bore spacing, a 90-degree bank angle, and two-valves-per-cylinder combustion chambers. (A notable exception is the LT5 engine that powered 6939 1990-95 Corvette ZR-1s; that V-8 had the 4.4-inch bore spacing but was topped with Lotus-designed four-valve heads.) The fifth-generation engine will definitely retain the original small-block features, continuing more than half a century of heritage and avoiding the expensive retooling that's required for new, clean-sheet engine architecture.

So what do we expect the next-generation small-block to bring to the Camaro and the Corvette? GM president Mark Reuss recently disclosed that there's a menu of advanced features that will be implemented on an as-needed basis during the life of this engine. Plan on:

1. The new small-block to arrive with the C7 Corvette in 2013.

2. Less piston displacement -- probably about 5.5 liters -- in the interest of fuel efficiency.

3. A compression ratio higher than today's 10.4-11.0:1, facilitated by direct injection's cooling effects.

4. Minimal deviation from the 430 hp at 5900 rpm provided by today's base Corvette V-8.

5. Significantly better gas mileage attributable to less displacement, a higher compression ratio, and likely use of cylinder shut-down technology (in GM lingo, Active Fuel Management).

6. Various forms of variable valve timing (VVT). Many current GM V-8s use one cam phaser to shift both intake and exhaust valve timing in sync up to 52 crankshaft degrees. GM has tested the cam-in-cam VVT system introduced on the 2008 Dodge Viper's V-10 for several years. This approach allows independent variation of intake and exhaust valve timing. Assuming it passes muster, expect it to appear in the Camaro and the Corvette as the key element of an "all-new advanced combustion system."

The advantages of the pushrod engine are hard to ignore. GM apparently feels that way, too, based on their future plans. I know when I recently tested the new Mustang and Camaro, the Camaro's OHV engine allowed it to attain higher speeds at less rpm than the Mustangs OHC. While some of this has to do with gearing and axle ratios, the OHC has to rev higher...more engine wear, more fuel consumption.
pushrods in a 21st century engine? ! sad

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