Feeding the power-hungry: when car enthusiasts ask for more, the automotive aftermarket and the...

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Most car owners are satisfied with the out-of-the-box vehicle they drive to and from work every day. But for some restless drivers, what's been handed to them isn't enough. These automobilists are served by the companies that design and manufacture parts meant to enhance

The automobile aftermarket industry meets the inherent desire of a niche of motorists who want more power, more character, more flash, and a bit of nostalgia.

"Many of our customers are taking cars like they had when they were a kid that they want to be able to enjoy with the family," said Bill Dyer, owner of Dyer's Blowers, Summit, Ill., a manufacturer of aftermarket superchargers. "They want to show the car but still want to take it out to the track."

Metal castings play a key role in helping car owners build their dream car, whether it's a rebuilt 1950 Chevrolet or a juiced-up 2007 model.

Filling the Niche

The U.S. automotive aftermarket is a steadily growing industry. From 1997 to 2006, sales grew 44.8% from $138.8 billion to $201.5 billion, according to the Automotive Aftermarket Industry Association. Sales of aftermarket parts for medium and heavy duty vehicles grew from $53.4 billion to $75.7 billion.

And while many of the main elements of aftermarket parts stem from typical automobile components, aspects of this niche industry call for a few design considerations of their own.

"The number one issue for design is the size of the target market," said Will Decker, design engineer for Crossroads Product Development, Salt Lake City, an engineering company with experience in casting design for automotive aftermarket components. "And that defines whether it will be cast, fabricated or forged. If casting is chosen, the size of the market defines which type of casting process is used."

Under the Hood

Re-built and high performance engines are the typical casting applications for the automotive aftermarket. Parts can include manifolds, throttle bodies, suspension components, supercharger components, transmission and engine housings, steering knuckles, gear boxes, adapters and end plates.

"Things you tend to use a casting for are more functional and mostly drivetrain parts," Decker said. "In the high-end racing sector, you see purpose-built engines and transmissions. In the four-wheel-drive sector, you see more ground clearance, more traction and bigger tires, so the drivetrain must handle higher stresses. Performance goals usually have to do with faster and taller Ire-design]."

Casting customers run the gamut, from the gearhead working out of his garage to multimillion-dollar racing teams. But the majority of the people who purchase aftermarket components are nostalgic car enthusiasts.

Professional Products, Hawthorne, Calif., sells engine parts for the aftermarket industry. Jim Davis, its chief operating officer, said the company's customers often fall into one of two categories.

"Our customers include those who have street rods, which are the cars made before 1948 that use a lot of special, customized parts," he said. "And those with muscle cars, which include cars from the '60s and '70s, as well as the current models of Mustangs, Corvettes and Camaros."

According to Davis, the most popular engine to revamp is the small block Chew, which did not change for more than 40 years. From an aftermarket perspective, this means a single manifold design can be used across Chevy models from four decades.

"More recent engine designs have shorter life spans," Davis said. "Which means more products must be designed to fit the array of engines."

Within the Envelope

One of the design constraints for aftermarket parts is that they must fit within an established space and function. The design also is limited by the available off-shelf components that a part will eventually interface with.

"At some point in designing, I'm going to stop making components and use what's already available," Decker said. "The standardization that exists is a big limitation and has an impact on how you design."

The metalcasting process has an advantage over fabrication or machining-from-billet, because it offers the designer the ability to put material where he or she wants it. This is useful when dealing with a limited envelope in which to fit a part.

Superchargers are popular aftermarket components. They can increase the power of an internal combustion engine without requiring major engine modifications. A developer of BMW aftermarket parts was working on a supercharger project that involved the installation of a 1.7-L displacement twin screw compressor and a three-core air-to-liquid intercooler into the same space currently inhabited by the naturally aspirated manifold of BMW 3.0-L and 3.2-L engines.

The pressure side of the compressor required a manifold and intercooler mount casting that met the space limitations of the design. The suction side of the compressor required the throttle to be positioned in such a way that it would not compromise the traction control system or the position to an existing air-inlet system. Using casting solidification modeling, 13 prototype parts for the supercharger were redesigned as seven castings--an inlet manifold, intercooler, intercooler end cap, intercooler outlet, throttle body adapter, nose support bracket and tail support bracket. The production version gained an additional 17 horsepower over the prototype on a 3.2-L engine for a total of 365 rear-wheel horsepower.

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Volume Considerations

Many rebuilt or high performance engine parts would be cast if they were part of the original vehicle design, but for the aftermarket, the metalcasting process is not always a given.

"You're dealing with a smaller market segment, and the customer may not have the resources for tooling," Decker said.

This often means machining the part from billet. Machining is expensive, but if only one or two parts are required, tooling costs for casting may be hard to justify. Decker points out that engineering costs also can be a factor when dealing with low volumes.

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"Most people shy away from casting as a process because it is more engineered," Decker said. "With 500 pieces, if the engineering cost is $10,000, that's $20 in each part. So as the volume gets smaller, the engineering cost becomes a big portion of the price."

But metalcasting quickly becomes more cost effective when the part is complex or volumes will meet the needs of more than a customer or two.

"You might choose casting for the amount of features that can be incorporated for the cost," Decker said. "You might increase the part cost but reduce the part count."

Davis purchases castings produced in permanent mold and diecasting facilities for Professional Products' lines of high performance and racing engine parts. The company also sells a limited amount of machined-from-billet parts, but Davis prefers castings because they are more cost efficient. Permanent mold and sand casting may require some machining, but diecasting the part can eliminate most of the process. A billet has to be 100% machined--a timely and costly process.

Cost and Cache

Aftermarket customers aren't necessarily looking for the deal of the century. Davis notes that many car owners are looking for prestige as much as performance, and building an engine at a discount misses the point.

"The cost is very high for machining billet. A billet is a solid block of aluminum, so you are machining away a lot of material. But in the performance industry, there is a certain cache in having a billet part because it is more expensive and has a one-off feel," Davis said.

Cars with aftermarket parts are going to be shown off, at car shows, at the race track, and in the driveway. Looks are important, and that engine hood is going to be popped for more than a cursory fluid-level check. So, along with the mechanical and physical properties the parts must exhibit to meet higher performance requirements, end-use manufacturers are looking at the aesthetics of the part, as well.

Dyer, who purchases castings molded in sand, says his company is strict on the aesthetic quality of castings he receives.

"We want a polished quality," Dyer said. "We don't want a lot of sand on the surface."

A machined-from-billet part may hold more aesthetic appeal for car owners, but Davis said the difference between a casting's appearance and a machined part can be negligible.

"In most cases, there's no advantage to billet," he said. "Once you polish a casting, it often doesn't look much different than a machined-from-billet part."

Decker argues that an engineered cast component holds a certain amount of swagger, as well.

"Let's say you're making a part for the four-wheel-drive off-road aftermarket. When you take a component welded in steel, just about anybody can do that," he said. "A fabricated piece that has been computer-designed by an engineer looks more professional. But when you show up with a casting, they see it as a really superior part. It gives it the look and feel of an OEM part, and it shows that your organization is very serious about design and engineering."

For More Information

@ "Put It in Reverse," S. Gibbs, ECS, September/October 2007, p. 16.

Shannon Wetzel, Senior Editor

@ Visit www.moderncasting.com to hear a podcast of Jim Davis, COO, Professional Products, discussing the auto aftermarket.