GM's Vortec 4200 inline 6-cylinder engine
by Jim Kerr

Bringing a new automotive engine to the marketplace is horrendously expensive. By the time all the tooling set-ups, durability testing, and emissions certifications have been done, the costs can exceed a billion dollars! It can also be exciting and rewarding. Just ask Tom Sutter, Assistant Chief Engineer for GM's new Vortec 4200 Inline 6-cylinder engine.

Recently, I had the opportunity to talk with Sutter about the new Vortec engine. His experience working on the Vortec 6-cylinder project has been an incredible, once in a lifetime experience. The design team was given a clean slate to design the best engine possible for GM's new SUV line-up: the TrailBlazer, Envoy, and Bravada. Nothing was ruled out initially.

The primary objectives for the new engine included: offer the performance of a V8 with the economy of a 6-cylinder, make the engine smooth and quiet, and use technology to reduce emissions. When evaluating engine possibilities, the inline 6-cylinder design became the number one choice.

So why an inline 6? Well, there's heritage. GM 6 cylinder engines debuted in 1920's on Chevrolet cars and trucks. The 1970's saw inline 6-cylinders disappear from cars, but trucks continued to use them up to 1985. But just heritage isn't enough.

Sutter described the inherent smoothness of an inline 6-cylinder design. It has both primary and secondary balance. Primary balance is when the crankshaft counterweights offset the weight of the piston and rod. Secondary balance is when the movement of one piston balances the movement of another. V6's have a secondary imbalance that causes engine vibration. Adding a counter balance shaft can reduce this imbalance, but that adds weight and complexity. The inline design was a good choice. The new Vortec 4200 engine runs smoothly, quietly, and quickly all the way to its 6200-rpm redline.

There are some difficulties in designing an inline 6-cylinder. The length of the engine allows more harmful torsional twist in the crankshaft, and makes cooling all the cylinders evenly more difficult. Stiffening the crankshaft helped reduce torsional twisting and a three part front crankshaft damper helps control twisting forces.

To keep the engine cool and as short as possible, the engine block and cylinder head uses the lost foam casting method for precision casting. Styrofoam patterns are placed in a sand mould and the molten aluminum is poured in, melting the pattern. The result is a casting so smooth that oil galleries do not need to be drilled. They can be used as cast! Specially-designed water jackets direct flow evenly throughout the block and around the siamesed cylinders, so cooling is equalized.

The steel cylinder liners have a small bore, only 93-mm, to help reduce the length of the block, but the stroke is long: 102 mm. Long stroke engines typically provide good low rpm torque and the Vortec 4200 is no exception. Over 90% of the Vortec's 275 lb-ft of torque is available from 1600 rpm to 5600 rpm. This engine pulls strong right off the line. With the truck in two-wheel drive, it is very easy to "smoke" the tires.

Technology abounds in the Vortec 4200. Four valves per cylinder, double overhead cams, computer controlled variable exhaust cam timing, roller cam followers, plastic intake manifold, electronic throttle control, and light weight alloy construction enable the Vortec 4200 to meet Low Emission Vehicle (LEV) standards and make lots of horsepower. At 270 hp, the 6-cylinder has 30 to 35 more horses that competitors V8's! All this with an estimated 20% fewer parts than a comparable "V" design.

Power is important, but so is durability. Of the more than 800 test engines built, twenty-four Vortec 4200's were tested on the dynamometer and all of them met the 150,000-mile target. Five of the engines were kept on the dyno running at wide-open throttle until they hit 300,000 miles - a test of astounding durability. They were all still running well!

According to Sutter, "This engine stands out in three areas - smoothness, power with even torque delivery and better fuel efficiency." After driving one, I have to agree.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

More Auto Tech...