1998 Chevrolet Corvette

Modern Pushrod PowerGeneral Motors Powertrain group was challenged to develop an engine for the C5 that would exceed the performance of the 5.7-liter/330-horsepower LT4 and deliver the thrifty fuel economy and squeaky-clean emissions needed to carry the V-8 into the next century. Engineers contemplated, should this V-8 be a modern dual-overhead-cam multi-valve engine, or should it have the "antiquated" pushrod valve gear that's been a Corvette constant?

For this Vette, the powerplant would need to be shorter and preferably lighter than its predecessor to complement the new chassis-hard to achieve with DOHC cylinder heads. Then there was the type of power the engine needed to produce. Tire-churning, instantaneous thrust is a Corvette hallmark; that meant a powerplant tuned for accessible torque first, and top-end power second. Project Manager John Juriga says ultimately the key deciding factor was that a pushrod design could develop more power while occupying less space than a DOHC engine. Decision made.

The Corvette's unique packaging requirements drove more than just its engine type-it also mandated transmission placement. To reduce crowding in the passenger compartment footwell area while maintaining the desired even split between front and rear weight distribution, the C5 became the first Corvette to use a rear-mounted transaxle.

The engine is solidly connected to the transaxle via a long 5-inch-diameter torque tube, with a metal matrix composite driveshaft spinning inside. Just three rubber isolated mounts connect the entire powertrain to the body-part of the reason behind the new Corvette's excellent noise and vibration attenuation.

The LS1 V-8 is completely new, and shares no parts with the previous small block V-8, which traces its lineage back to the '50s. Throughout, the LS1 employs the latest GM engine technologies to relegate the long-standing limitations of the old small-block to the annals of history. The new aluminum engine block has unusually deep skirts below the crankshaft, plus a structural aluminum oil pan. Not only is it stiffer and quieter than the old iron block, it's also 88 pounds lighter.

With a longer stroke and a smaller bore than the old engine, the new V-8 now displaces 347 cubic inches, compared to 350. To create a lighter, more efficient valvetrain, the pushrod valve gear was positioned 'in-plane," eliminating side-loads and reducing friction. Advanced materials and systems abound, like the equal-length-runner thermoplastic intake manifold and new lightweight double-wall stainless steel exhaust manifolds. Throttle-by-wire technology improves the engine's response and is integrated into the traction-control and anti-lock brake systems. The LS1 nails the required power targets and manages to be cleaner, more durable, lighter, and quieter than the engine it replaces. Pushrod engineering has entered the modern era.-Jeff Karr