The new C5 Corvette 350 Engine

The Chevrolet Corvette

LS1 Engine - As found

in the C-5 Corvette

 

The common thread throughout most of the Corvette's 44-year life has been Ed Cole's fabled small-block V8. Not only has it powered the Corvette since 1955, but it was largely responsible for Chevrolet's resurgence in the 1950s and 1960s. The small block, one of the most versatile high-performance engines of all time, has more race wins than any other production-based V8. In light of all this history, the General Motors Powertrain group had a difficult decision to make when it came time to develop an engine for the new car: keep the legend, or go with the increasingly popular multi-valve, overhead-cam technology? The latter was used with the 32-valve LT5 powering the ZR-1, which went out of production in 1995.

The engineers were under no orders to retain pushrod technology, nor were they pressured to turn to overhead-cam designs. They weighed performance, packaging, weight and cost. The target was a traditional 350 cu. in. with 345 hp and 350 lb.-ft. of torque. However, for packaging reasons, the engine needed to be shorter than its predecessor. The team decided a lighter engine would be nice too. With these goals in mind, the engineering team developed a completely new small-block.

Enter the LSI, an all-aluminum, more mature 350-cu.-in. small-block V8; one that is lighter and runs cleaner than any small-block yet. The LS1 also produces the targeted 345 hp at 5600 rpm (compared to the LTI's 300 hp and the LT4's 330 hp) and 350 lb.-ft. of torque at 4400 rpm. That's good enough for a 4.7-second 0-to-60 time and a 175-mph top speed.

"The small-block's simplicity helped make its case, as did its compact and efficient size - a major benefit of pushrod designs," said project manager John Juriga. "We felt we could do the best job overall with a pushrod design rather than an overhead cam, because more power could be squeezed from a more compact unit. It wasn't an easy decision. It took a long, long time to decide." Corvette enthusiasts will no doubt applaud the power increase, but the key, as Juriga pointed out, is the power's usefulness. "In the upper rpm ranges," he said, "this engine just wants to keep revving. By about 4000 rpm, the LTI's power and torque flatten out. This engine's higher torque curve allows it to keep right on pulling beyond 5000 rpm." Better breathing is one of the main reasons the LS1 can rev beyond previous Corvette engines, thanks to the LS1's well-designed cylinder heads (cylinder-head design is one of the most important aspects of a pushrod engine's performance).

The LSI's aluminum cylinder heads and intake manifold were designed as a single system to optimize airflow and fuel-flow efficiency. All of the I-SI's 15-inch intake manifold runners are identical, resulting in a constant airflow. The intake runners also help the air flow more smoothly into the engine and help the engine idle better. The fuel injectors have been placed for the most direct fuel spray possible. Bosch's sequential fuel-injection system has been modified to perform with the manifold's fuel runners. The glass-filled nylon (plastic) intake manifold is easier to make and weighs less, as GM learned while developing plastic manifolds for its 3800 V6 and Northstar V8. The cylinder-head geometry has been completely reworked for the best airflow and fuel flow, thus producing the most potent fuel-burning possible.

Engineers knew that the LT4 valvetrain experienced side load because the cylinder-head geometry wasn't in plane. To compensate for the side loading, larger components were needed, which limited the valvetrain's speed and efficiency. So the engineers designed the LS1 valvetrain to be in plane to reduce component stress. Once this had been achieved, developers were able to use lighter components. As a result, the valvetrain is quieter because it's easier to control valve opening and closing speed. Engineers also chose cast-steel, roller rocker arms (replacing the LT4's crane rocker arm) because they are more rigid. "This engine feels anxious," said assistant chief vehicle engineer John Heinricy. "It has what we call 'race to redline,' meaning it likes to be revved - to run at the high rpm ranges."

Heinricy added that maintenance is easier with the LSI's 100,000-mile platinum-tipped plugs and 10,000mile oil change intervals. Beyond better performance, C5 owners will also notice a big reduction in engine noise and vibration entering the cockpit because the block has been completely redesigned, with stiffness, strength and low weight in mind. The block, now made of aluminum (which cut its weight from the cast-iron LT4's 195 pounds to 107 pounds), has deep skirts extending approximately 40 mm beneath the crankshaft centerline. This "deep-skirt" design adds strength to the block. The lower skirt makes the flat oil pan rather shallow, but two oil reservoirs on each side of the pan eliminate oil starvation during hard cornering. The six-quart pan is cast aluminum, and it does double duty as an engine structural member. The LSI has no oil cooler, so engineers recommend Mobil 1 oil. Corvette engines have been filled with Mobil 1 from the factory since 1992. Conventional oil is good to temperatures of about 280 degrees, but Mobil 1 can take 300 to 325 degrees.

The block has a four-bolt cylinder head pattern instead of the historically common five-bolt. Engineers said the four-bolt pattern allows the tops of the bores to stay rounder longer because the block deck is not being spread unequally. Additionally, the cylinder-head bolts are more than 50 mm longer than before. With the longer fasteners, bolts can take the relaxation of the gasket and still have enough energy stored to maintain clamp load. GM powertrain engineers said the bolts will not need retorquing. Each LS1 piston is 6 mm shorter than the LT1's and weighs just 15.38 oz., which helps the engine rev more freely. The crankshaft, made of nodular iron (which contains graphite), has drilled mains for lightness.

The oil pump is mounted on the front of the crankshaft. This crank-driven pump is more efficient, using less energy to move the oil, particularly at low speeds and cold starts. The new camshaft is again made of steel, but it is a shorter, stronger unit. Larger journals reduce unit loading, allowing for more aggressive cam profiles. The cam's center has been drilled to reduce weight. The exhaust manifold (made of stainless steel) is a dual wall design. A gap between the walls contains air and acts like a thermos. This retains exhaust gas heat on the way to the catalyst. Perhaps technical illustrator David Yimble summed up the LSI best. "This is a very well-thought-out engine in the same way a Rolex watch is well thought-out," he said. He should know. He's not only a pushrod enthusiast; he's been studying the LSI, part by part, for a number of years. "It's amazing what GM has done. This is one of the highest-output two-valve engines I've ever seen in a production car."


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