Use of plastics in powertrain applications continues to heat up. Automakers increasingly are turning to plastics as they try to combine parts and eliminate costs, analysts say, projecting big growth for plastics in fuel rails, rocker arm covers, air cleaner housings, oil pans and, of course, intake manifolds.

The biggest transition to plastics for the next several years will be in fuel-handling components, says Jim Best, president of Market Search Inc. The conversion to nylon intake manifolds will continue to increase over the next few years, then spread to other components of the air/fuel system, including the fuel rail and air filtration devices.

General Motors Corp.'s new GMT800 pickups are switching from steel fuel tanks to plastic, and that alone - because of the high production involved and the large size of the parts - amounts to a huge new piece of business for plastics.

Throttle bodies, which are essentially electronically controlled carburetors, also are switching to plastic as automakers strive to lower the cost and weight of older engine designs.

Within the next 10 years, nylon intake manifolds will grow to at least 60% of the market, Mr. Best says, up from 12.6% in 1998. Overall, Market Search projects a 41% increase in the use of underhood plastics in North America, jumping from an estimated 382 million lbs. (173 million kg) in 1997 to 538 million lbs. (244 million kg) by 2007.

The University of Michigan's Office for the Study of Automotive Transportation, meanwhile, projects the use of plastic rocker arm covers to grow from 15% of the market today to 30% in 2002 and 50% in 2007. Fuel rails will increase from 5% of the market today to 20% in 2002 and 35% in 2007. Despite growth in these areas, plastics are not expected to make inroads in components such as engine coolers, heater cores, radiators or transmissions.

One of the major benefactors of the move to nylon intake manifolds, DuPont Automotive, aims to increase market penetration with the help of a new welding-enhanced 66 nylon resin. The new material marries the high-temperature and mechanical performance properties of traditional 66 nylons, the company says, with the strength and cost benefits associated with type-6 nylon.

The new material will debut on two vehicles in 1999, one in North America and one in Europe, says Charles Stutz, DuPonts automotive industry leader marketing manager. He declines to identify which models, though.

Three more manifold applications will be added in the next two years, Mr. Stutz says, with the possibility of moving into valve covers, air filtration, throttle bodies and fuel rail components soon afterwards.

DuPont also has developed a new blow-molding technology for underhood thermoplastics. The technology, commercialized in Europe in 1996, will help automakers integrate various components and lower costs, Mr. Stutz says.

A typical rubber/metal air duct, for example, can include as many as 23 parts and 14 assembly operations. Using the blow-molding process, the component can be produced in seven parts and eight assembly operations, yielding an overall weight reduction of approximately 70% and a 50% cost reduction. Potential candidates for the process include air ducts, hoses and reservoirs.

Hoechst Corp.'s Ticona polymer unit, meanwhile, is targeting a number of components for conversion from metal to thermoplastics. Potential areas include transfer cases, housings, bearing cages, torque converters and valve bodies.

The company already supplies cooling system components to Big Three automakers, says Jonas Angus, Ticona's sales and marketing manager-powertrain/chassis. As automakers continue to use high-mileage coolants, Angus says, anti-corrosive thermoplastic will become a necessity.

"The other area where we see a good fit is the crankshaft flange," Mr. Angus says, noting that most of these units currently are made of aluminum. Using a thermoplastic like Fortron (Ticona's linear polyphenylene sulfide), we can consolidate a number of parts and reduce costs by 20% to 25%. This could be in production in the U.S. within the next couple of years," Mr. Angus says.

For the first time in North America, plastic is replacing aluminum under the hood in a throttle body application, says Larry Bell, director of the underhood market segment for GE Plastics. The first high-volume plastic throttle body was developed several years ago in Europe by Britain's Rover Group Ltd. using DuPont's Zytel nylon 66. But North American honors for the first replacement of a metal throttle body go to GE Plastics' Ultem amorphous thermoplastic polyetherimide (PEI) resin.

Mr. Bell won't divulge which '99 model vehicle gets the first plastic throttle body, but he says the new part is 40% lighter than the previous aluminum component. It's also 30% to 40% less expensive to produce because plastic can easily be molded into the required complex shape. The previous metal assembly required extensive machining operations.

Mr. Bell says the new throttle body application is significant because it's a precision plastic part that's proven it can maintain tight tolerances over the life of the vehicle, despite the extremely harsh conditions under the hood.

For instance, the throttle body must resist shrinking, expanding and cracking in temperatures ranging from -40F (-40C) to +300F (+148C). In total there are about 14 programs currently under way to replace metal throttle bodies with plastic, Mr. Bell says. - with Drew Winter