Thursday, May 28, 2020

Plastic Performance: The Story of the Innovative Polimotor Engine

Photo Credit: Jack Webster



The engine compartment for a traditional fuel-burning automobile is one of the most incredible storms regularly occurring on this planet. Intense heat of the combustion process combines with a stunning electrical storms and powerful mechanical forces to create the momentum we take for granted. Harnessing and managing this essential storm to generate optimum performance relies on the ability to engineer the best possible engine. 
Among one of the aspects carefully considered towards the construction of a traditional internal combustion gasoline engine is material selection. Performance, durability and importantly cost factors into how to produce a powerplant. For a long time, cast iron was favoured for the construction of engine blocks for most production automobiles while other components utilized alloys such as stainless steel. Previously existing in high performance or more expensive vehicles, aluminum has gained wider acceptance in recent years as usage of the material has become cost effective. Aluminum’s performance in engine construction functions competitively with the materials it replaces but has the additional advantage of being lighter weight. While aluminum is currently popular in automotive construction (with usage spanning throughout new vehicles), there was also realistic effort put forth to investigate building powerplant using more unorthodox methods during the late 1970s into the 1980s using polymers and composites to achieve a significantly lower weight.


Photo Credit: Ford Motor Company


Originally developing engine parts for racing, mechanical engineer Matthew “Matti” Holtzberg began envisioning the use of polymers (generally referred as plastics) for the manufacturing of high performance components. Establishing Polimotor Research Incorporated in 1974, Holtzberg’s started to experiment on materials and construction methods. Composite-constructed connecting rods, valve springs and push rods were some of the first engine parts he was able to create beginning to sell the components for use in motorsports. By the end of the 1970s, Holtzberg had loftier plans to exploit the benefits of alternative materials on a greater scale. Though not the only time a plastic or non-metal internal combustion engine was conceived, this development and later testing represented a major effort to determine such an application in real-world motoring.


A Plastic Dream Coming True


Meeting with employees of the Ford Motor Company, Matti Holtzberg was encouraged in 1979 to create an engine made entirely out of polymers or composite materials. In pursuit to prove the merits of the innovative powerplant components, Holtzberg utilized the design of Ford’s 2.3-liter four-cylinder Lima engine. Not as celebrated as Ford’s larger power units, the Lima engine design impressively served from 1974 to 2001 on a wide range of the automaker’s vehicles. The naturally-aspirated and turbocharged versions of the 2.3-liter powerplant would propel the Ford Mustang starting in 1979 model year demonstrating some (if limited) performance viability ahead of Polimotor’s development on the composite engine. 


Photo Credit: Ford Motor Company



Due to the extreme heat and stresses involved in an internal combustion engine, Polimotor quickly realized there were some technical restrictions that would make an entirely polymer-based power unit impossible with a half-melted plastic piston reflecting the situation. Instead, an experimental engine would include steel and aluminum components where required. The crankshaft and camshaft were sourced from the Ford production engine while the exhaust valves and valve springs were also metal. Several other parts applied to the Polimotor engine build utilized hybrid polymers/metal construction. The intake valve and pistons were assembled by a combination of aluminum with a highly heat resistant polymer called Torlon. Marketed by Amoco Chemicals through the 1980s, Torlon has a multitude of attractive properties. Capable of withstanding temperatures greater than 500 degrees Fahrenheit (260 degrees Celsius), the primary benefit of the reinforced polymer is the ability to create low weight parts.  

Through the use of a block made from a fiber-reinforced polymer, Torlon and the sparing space of metals, the experimental engine based on Ford’s 412-pound Lima four-cylinder powerplant weighed approximately 160 pounds (some published accounts listed between 152 and 168 pounds). Some components contained in the Polimotor engine were remarkably lighter than conventional parts. Intake valves would weigh 79 percent less using a combination of aluminum/Torlon construction compared to steel pieces tipping the scale at just 30 grams. A weight decrease of roughly 60 percent was achieved with the adoption of valve spring retainers and tappets made completely out of Torlon. The engine’s pistons were also formed using the high performance polymer but the extreme heat of the combustion chamber would immediately be observed (Matti Holtzberg kept a melted prototype piston in his office). An aluminum crown was applied to the top of the piston that also would be surrounded by a steel wall in order to handle standard combustion temperatures. Despite the compromise needed, a piston in the four-cylinder engine was about 109 grams less than a fully aluminum counterpart. 


Image taken from Amoco Chemicals Torlon Brochure of
engine components created by the material.


The Polimotor engine also exhibited two additional benefits afforded through use of the lighter components. Able to run up to 30 percent quieter than a cast iron engine, the most impressive advantage was improved performance. The lower weight of moving parts contributed to the creation of an engine producing 318 horsepower with a maximum redline of 14,000 rpms. While Ford Motor Company’s Special Vehicles Operations tested and researched the potential of a production variant of the Polimotor engine, the worth of the powerplant would also be trialed in the more public arena of motorsports.


Fitting the Racing Mold


Matti Holtzberg had sights set on auto racing throughout the time he worked with the notion of a plastic engine. While open wheel racing was seen as a possibility, sports car racing proved to be the primary showcase for the unique powerplant.



Photo Credit: Jack Webster


Creating a 2-liter version of their experimental four-cylinder engine, Polimotor’s technology was field tested on sports car circuits. A #8 Polimotor Research entry based on a Lola T616 chassis was entered in a pair of IMSA sports car races during both the 1984 and 1985 seasons. Racing twice at Watkins Glen in 1984 in the GTP-class category, the Polimotor entry driven by Peter Kuhn failed to finish the 6-Hour event in July but was able to complete September’s shorter 500-kilometer race taking the checkered flag in 35th place overall. The #8 car also ran at Road America finishing 56th overall in the 59-car field. The following season, the car was entered into three more events in the IMSA’s Camel GT Lights category returning to Road America as well as participating in events at Mid-Ohio and Lime Rock. Wearing Amoco Chemicals sponsorship through all but one of their outings, the Polimotor race program was short-lived and produced limited success finishing half the events it was entered in but was not in contention for overall or class wins. During the mid 1990s, the Polimotor engine would race again in a different of motorsport. In the British Hillclimb Championship, the power unit proved formidable against other 2-liter racing engines.


The Reality of a Composite Engine


Roughly 35 years since the last IMSA race for the Polimotor engine, we are obviously not driving road vehicles using the innovative construction technology. So, what were and currently exist as obstacles for plastic-based powerplants? 
One of the major drawbacks to the concept of the Polimotor engine concept related to the price of materials. In 1983, the price of carbon fiber was projected between $20 and $40 per pound. Although price for the same amount of carbon fiber material today is estimated at around $10, the cost is much greater than aluminum currently rated at roughly $0.80 per pound. In a 1980 article from the Chilton’s Automotive industries periodical, Matty Holtzberg claimed to have orders for more than 100 early examples of the four-cylinder Polimotor engine listed at a price of $28,000 for companies seeking to evaluate the technology. At that time, a mass-produced Polimotor’s cost would have been estimated at $2,500 a piece. A similar designed engine using traditional construction was priced at around $1,000 for a vehicle retailing for about $5,500 in 1980. The cost effectiveness of composite or polymer-based engines has not likely improved to the extent that meaningful production is possible. 


Photo Credit: Ford Motor Company



The long-term endurance of the Polimotor engine technology can also be viewed as a question mark. Although it demonstrated durability in IMSA sports car competition in the 1980s, there’s not a great deal of information identifying how well such a powerplant would survive challenges of everyday driving for years. During the early development of the Polimotor engine, Matti Holtzberg explained there were complications in fastening components as threaded bolts were prone to separating too easily and adhesives lacked the heat resistence needed in the application. Though one method was found for the 1980s Polimotor engines, new adhesives or assembly procedures may be available today assuring greater performance. More extensive testing of a polymer or composite based engine might deliver clear answers. 


The Present and Future of Composites in Engines


Though composite or fiber reinforced polymers may not be used for extensively for engines, this material technology has been employed in a limited extent in modern passenger vehicles. Since the 1990s, several automakers have engineered composite polymer construction into air intake manifolds. Subjected to lower temperatures within the engine compartment, the intake manifold has been a suitable candidate for being made of plastic allowing for weight savings of up to 40 percent compared to an aluminum conforming to the same design. Ford, General Motors and Toyota have all sold vehicles equipped with polymer-based intake manifolds for several decades.
A major sports car builder has recently expressed a desire of using composite components in a more active position inside a production car engine. Lamborghini made news in 2016 stating an intention to create carbon fiber connecting rods for a future V-12 engine being developed to power the successor for the Aventador. Already used in Lamborghini’s patented Forged Composite material has demonstrated incredible strength as well as lightweight properties. Originally planned for the replacement of their flagship supercar in 2021 or 2022 but the release date deeper into 2024.


Photo Credit: Chris Nagy/ CAR FYI



It’s also worth noting that the idea for an engine made largely of plastic components has not died in the heart of Matti Holtzberg. Through his current research, the Polimotor engine concept continues to present itself with innovative potential. With Polimotor 2 and Polimotor 3 designs, Holtzberg has been utilizing modern fiber reinforced polymers and dives deeper into realm of experimentation. The creation of polymer and metal components is now being envisioned as constructed with 3D printing. According to the website for Holtzberg’s Polimotor LLC company, plans are to run a sport prototype car in the Florida-based FARA racing series in 2020 and has ambition to compete in hill climbing for the 2021 season. 
As automotive engineers continue to develop stronger, lighter, better performing engines, evolution will lead to the ongoing exploration of new ideas or the possible revisiting of previous ideas with the benefits of updated understanding. 


References:

Keebler, Jack "Ford's Impossible Plastic Engine." Popular Science September 1982

Szigethy, Neil M. "What...A Plastic Engine?" Chilton's Automotive Industries December 1980