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An inside look at the new vette engine

An inside look at the new vette engine

Warren, MI--Sometime in January 1997, Chevrolet officials will finally take the wraps off the new fifth-generation Corvette. The so-called C5 Vette will be the first redesign of the classic American sports car in 13 years, and engineers at the GM Tech Center are shrouding it with a level of secrecy that would make their ancestors on the Manhattan Project proud.

But, while the details of the Vette redesign are murky at best, the picture of what will be under the hood is clear. The small-block V8 that was born in 1955 and powered past Vettes (as well as Camaros, Monzas, and Monte Carlos) has matured as a lighter, stronger, more rigid engine. It retains the push-rod design to conserve mass, but is different from earlier versions in almost every other respect. Among the changes:

- An all-aluminum, deep-skirt block that's 80 lbs lighter than its predecessor.

- A four-bolt cylinder-head design and new head-bolt fastening geometry that eliminate bore distortion.

- Smaller and fewer fasteners.

- A refined intake manifold made of a new composite that enhances performance.

- Redesigned powder metal connecting rods that increase strength.

- Ignition coils located near the spark plugs for high ignition energy and more efficient combustion.

Work on the new engine--the 5.7l, 350-cubic inch V8 LS1--began in 1991. At the outset, engineers decided to marry the engine and power train with the new Corvette. "Usually, you have to shoe-horn a new engine into an existing vehicle, but planning it for the Corvette gave us the freedom to start from scratch," says LS1 Product Manager John Juriga.

Using EDS Unigraphics CAD software, Juriga and his team worked toward several objectives in designing the engine, including lower mass and noise, vibration, and harshness (NVH); better 0-60-performance; and good low-end torque. The design is rumored to be applicable for other cars besides the Corvette, though GM's Powertrain Group won't comment on any future applications just yet.

The 350-cubic-inch displacement was a given, as was a minimum of 340 hp. The need for good low-end torque, lower mass, and cost control pointed them toward the push-rod design. "The absence of overhead cam components meant lower mass," Juriga says, "Two-valve engines provide very good low-end torque while four-valve designs falter there."

In a special private meeting at the GM Tech Center, Juriga dissected the engine for Design News. Here are the technical details:

A.Oil pan. The light-weight aluminum pan is a structural member designed to reduce powertrain bending. Additionally, it has an intricate baffle system with reservoir pockets to ensure a good supply of oil to the pick-up tube, even during the 1g turns Corvette drivers often make.

B. Bearing caps. Made of powder metal, they were designed to reduce drag. Locating "ears" on the set cap eliminate the need for side set screws.

C. Crank shaft. It's made of nodular iron, and is undercut and fillet rolled. It is much stronger and stiffer than its predecessors. Crank pins are drilled for mass reduction and bay-to-bay breathing.

D. Deep-skirt design. Traditionally, block ends at the center line of the crank shaft. GM extended this block down past the main bearing caps for rigidity. Two bolts tie the bearing cpas to the block from the side. Though the block bends fore and aft and side to side, as any highly stressed component would, it still is stiffer than previous designs, reducing noise, vibration, and harshness.

E. Valley cover. It's a rigid aluminum piece that prevents bowing of the block.

F. Four-bolt head design. Four long head bolts (not the traditional five) are threaded into the block itself by way of through holes. The objective was to avoid distortion at the top of the deck. The head bolts are twice as long as the old bolts, and store energy as they stretch. As gaskets compress over time, they will lose some stretch, but there will still be plenty of stretch left in these bolts. Short head bolts, on the other hand, lose clamp load over time with the relegation of gaskets, and that could cause head leaks. Additionally, with the long head bolts, rings seal better to the bore for better emissions. Tension on the piston rings goes from 10 lbs to 7 lbs for better fuel economy.

G. Piston design. A redesign took 100 grams out of the piston weight, which results in less stress on the crank shaft. The weight reduction resulted from decreasing compression height of the piston. Tighter piston-bore clearance of the skirt-less pistons eliminates noise.

H. Cylinder head knock sensors. Threaded into the valley of the engine (unique to GM), they pull back spark advance if the detonation is too powerful. Power and fuel economy are improved while avoiding engine damage. Holes in the block valley improve breathing bay to bay.

I. Intake manifold. Supplied by Bosch, the composite manifolds consist of 33% glass-filled nylon 6. Engineers chose the composite to reduce mass, but got air flow and temperature advantages as an extra benefit. The aluminum previously used for manifolds transferred heat to the intake, but the material is expensive, Juriga says, and it doesn't dampen noise as well as aluminum. Nevertheless, valve components lower overall engine noise. All fasteners are integrated. Pressured-in-place gaskets fill voids when compressed and require little clamp load for sealing. The manifold seals air only. No oil or water leaks through. The LS1 uses the Northstar-style dual-wall manifold to keep gas warm to let the converter heat up faster. Shape design eliminated turbulent spots that caused hot spots which, in turn, could cause cracks.

J. Rods. Made of powder metal, rods and caps are molded as one. Rods are machine-grooved in caps and then fractured. The fracture results in rough spots that make the rod and cap go together better. No nut required, just a bolt.

K. Ignition system. Coils are on top of the rocker cover. The intent is to get as much ignition energy as possible to each cylinder. The traditional GM system is one coil for every two cylinders, but the LS1 has one for each cylinder. Juriga says that design provides extremely high ignition-energy capability for improved combustion.

L. Fuel ignition. Sequential fuel injection system supplied by Bosch. Injectors are conventional, but the system incorporates a crank sensor and cam sensor for fuel timing.

M. Electronic throttle control. There is no mechanical cable to the throttle, a first for GM's gasoline engines. (GM does produce a simple diesel system to govern fuel only.) Electronics give infinite ability to open and close the throttle at will. Mercedes and BMW have similar systems. The system integrates cruise control and traction control.

N. Cam shaft. Steel-billet, gun-drilled, to make it hollow in the center for mass reduction.

O. Lifter restrictors. Made of composites, they stop the roller lifter from rotating.


LS1 engine specifications

Feature

Type
Cylinder head
Block
Hydraulic lifters
Bore and stroke(inches)
Cam drive
Redline (rpm)
Displacement (cubic inches)
Compression ratio
Hp @ rpm
Torque (lb-ft) @ rpm
Exhaust system
Ignition system

Spec

5.7l V8 SFI
Cast aluminum
Cast aluminum
Yes/roller
3.9 3 3.62
Roller chain
6,200
350
10.1:1
345 @ 5600
350 @ 4400
Stainless steel
Coil near plug
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