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Birth of the 928 Integrated Bumper

he wouldn’t give it up.

“That 911’s a ’72…the external oil filler flap right behind the passenger side door gives it away. Did you know that? You can’t call yourself a Porschephile if you didn’t! It was the only year a production 911 would employ a feature Piëch developed for the 911R. So technically, you…”

I was trying to shake this m**********r off me. like a tick, he latched on trying to bury his head into my skin while pounding my ear with condescension. I had enough of this guy’s b******t; I barked…
“GODDAMNIT! who are you? what the HELL do you want?”

cutting him off in mid-sentence, he just stood there staring at me. he looked me over; oil stained boots, soiled threadbare dungarees, moth eaten wife beater, and pronged dog collar. he sniffed, thrust his hands in his pockets and aimed his eyes at mine.

“are you trying to impress me or something? well, you’ve failed because the s**t you’ve been reciting is F*****G amateur. you know what? I FORGOT more than you know.” I blurted out.

I wasn’t finished with this smug c********r yet…I went for the throat.

“what’s your name?”


“OK, Artie, see that 928?” nodding my head at the Moccabraun ’78, “in September of ’72, the 26th to be precise, engineers in Zuffenhausen set up an integrated bumper project group to create the polyurethane bumper covers on that thing. now, had you said that to me, I would’ve been MILDLY impressed.” I turned my head back to him and walked away.

I’m amazed at what I recall from random memory during fits of lunacy…let me share it with you while it’s still warm.

Bayer’s 1967 K-67 launched at the 1967 International Trade Fair for Plastics in Düsseldorf, Germany

they shook their heads.

the initial sketches of the 928 followed Porsche’s trademark of integrating the bumpers into the body. the 356 had them painted in the car’s color, and despite America’s pendulum test, 911s wore them too…although designers had struggled a bit to pull it off. so why the hell were clan behind the 928’s creation seeing new sketches with the 928 wearing partially integrated bumpers that looked like an afterthought?

well here were the goddamned engineers, the stiffs, ruining the party with typical right-brained worries.

“Impossible, they won’t be sturdy enough…”

“Never mind that Reiner, the paint will turn a different shade than the rest of the car over time…and more importantly, the paint can’t flex as much as the bumper.”

“No…you know what the real problem is Dieter? Those Arschlochs draw s**t without any goddamned idea of how it’ll be made!”
“Balls! Give the engineering department back the original goddamned sketches and tell them to figure it out.”

the Project Fathers didn’t want to hear it.

“Balls! Give the engineering department back the original goddamned sketches and tell them to figure it out. The original design had integrated bumpers, it was unanimously approved, so we must go forward.”

they had to put the hammer down. production of the 928, a completely new car, was a few years away and there wasn’t even a full working prototype made yet…the bumpers were just one of the headaches; the fuel tank, rear suspension, engine, needed some hard thinking and prototyping.

the Feds in America were another problem. they were cracking the whip on European and Japanese imports wearing bumpers sculpted in tin foil. word in the industry was that any car manufacturer wanting to sell their wheels on our soil in 1973 must have rear bumpers able to absorb a 2.5mph shunt, and front ones to absorb a 5mph shove.

creating fully integrated bumpers in Polyurethane wasn’t some mystery formula scribbled on scrolls, it was doable. If Chevrolet were introducing them on their 1973 Corvette, and Pontiac had them on their ’73 Firebird — pfff. in four weeks, engineers rang up 17 firms that had the answers they were looking for regarding specifics in manufacturing, materials, and processes.

the fist hit the table and a decision was made. the bumpers were to be made of Polyurethane as either a molded skin with an aluminum beam hiding underneath to provide the protection, or an injection molded Polyurethane unit using and internal air chamber system for impact absorption.

the process of manufacturing, more specifically injection molding, Polyurethane components for the auto industry was pretty young…but polyurethane wasn’t. Otto Bayer, no relation to Bayer AG, and his co-workers at the German chemical company IG Farben (who in 1925 merged with Bayer AG), created polyurethane in 1937. by 1952, the polymers used in creating polyurethane became commercially available, and by 1954, Polyurethane foam became one of the derivatives. in ’56, Dupont stepped in to further refine these polymers making them safer, cheaper, more water resistant, and ultimately, more popular with the help of BASF and Dow.

the introduction of other chemicals and reactionary agents spawned more hypothesizing, experimenting, and concoctions of all sorts came to a head during the early-mid 1960s. in 1967, a revolution that’d be both praised and cursed began…Bayer exhibited a car made entirely of plastic (save for the engine, gears, and wheels) at International Plastics Fair in Düsseldorf, Germany — the K67.

lots of hands were clapped together and vigorously rubbed after that little show because Bayer AG had created the manufacturing process that produced the panels on that car; Reaction Injection Molding, or RIM.

here’s how the process works. a couple of reactants (chemicals and polymers) are stored separately. at the ready is this industrial phallus aimed directly into a mold where the two chemicals are shot at 2000psi into the hot pocket where the streams mixed, reacted, and formed the molding. the result is ejected in a few minutes; depending on the size and complexity of the part, of course.

the reaction part of the process is the variable, if the part being made required extra strength, flexibility, elemental resistance, thermal expansion and stability, fibers, milled glass (mica), or fillers could be added to one of the reactants. this now becomes a new process called RRIM; Reinforced Reaction Injection Molding.

oftentimes, there’ll be an abbreviation of PUR hitched to RIM or RRIM; that’s PolyURethane. now, the specifics of this process are found in thick bindings at your local library if you’re boring enough to want more insight. for the purposes of this paper, it’s more than enough information; let’s move on.

Porsche swooned over this process the moment it wafted into their ears. anything to ease manufacturing, allows exponential creative liberties (styling), be corrosion resistant, and most of all, reduce weight, tickles their Stuttgarter Wurst. they bear hugged it.

Poly was a wide-hipped woman in bloom, oozing fertility winking and blowing kisses from the second floor balcony seducing Porsche’s designers and engineers…they saw potential. further investigation drew out more conclusions like dimensional stabilities in extreme temperatures, resistance to abrasions, and forgiving to insignificant damage. Porsches using components made of PUR would yield increased fuel economy, increased service life, allow for scratch and gravel resistance finishes, smoother body surfaces for reduced aerodynamic drag and improved pedestrian protection.

so in 1969, they began using RIM parts in production cars…the 914 was first. if you imagined fenders, hoods, and doors…stop. they decided on producing a trim panel with tight curves that forming a transition between the bumper and the body for MY1970. they were offered in black only because there were no feasible paint options available yet; a fine grain on the visible surface was the best they could do. the covers and the upper edges of the door trays were also made of RIM; not a very exciting start, but they got more adventurous with each model year. in all, about 20.4 kg of RIM components went into the 914.

1970 914 displaying Porsche’s first stab at using PUR-RIM on its front bumper

1975 911 Turbo Carrera flashing the 911’s use of PUR-RIM bits

in 1972, the 911 was the second dog to lick the spoon. PUR-RIM pieces were used for bumper trim pieces and energy absorbing elements. then front and rear spoilers were developed using urethane. when the Turbo blasted in, black PUR-RIM graced its bumpers, chin, and massive rear spoiler where a careless pedestrian would be spared stitches if they knocked into the thing. steering wheels, horn pads, shift knobs, and flag mirrors surrounds were also made with PUR-RIM. still, no paint solutions were available…so they stayed black.

Piëch’s 911R missed the technology by a couple of years. the hood, fenders, door skins, and decklid would’ve been perfect candidates for PUR-RRIM rather than the expensive process of hand-laid fibreglass Karroseriefirma Baur had to do, nevermind sparing Rolf Wütherich from drilling holes by hand. even though the R’s problem was more about marketing than cost, Huschke von Hanstein might’ve had more leverage from a monetary perspective when pitching the idea to marketing.

the 928’s integrated bumper group was stalled with the challenge of finding suitable paints and primers for the proposed PUR bumpers. sure, they could be manufactured, but if they couldn’t paint the things, they were wasting their time…leaving them black certainly wasn’t an option.

engineers weren’t f*****g around here; they went deep into studying every possible paint variation to yield the performance they demanded. one of the issues was variance in paint shades as it aged under the nastiness of the elements, ultra-violet rays, and leaching of the PUR chemicals through the finish. the body required one type of paint while the PUR bumper skins needed another because of the elasticity requirements, so there had to be consistency.

they worked, and worked, and worked with the paint industry until they finally found a brew that met every demand, especially the aging one. the metal would be sprayed with alkyd-melamine resin while the PUR (polyurethane) parts got a two-component, polyurethane-based paint. the elasticity of the PUR paint had to have the same flexibility as the polyurethane material of the bumper skin…period. the test results induced much back slapping, a*s grabbing, and beaming smiles. the swatch of material they painted was cooled down to 0°F and bent 180° with a sadistic bend of around 7/8” without a single crack in the paint. further tests including abrasion, being splashed with chemicals, adhesion, and weathering further convinced engineers that yes, this was their paint.

with the paint cloud gone, the modelers got the nod to proceed with a 1:1 plasticine model with integrated bumpers for approval—it was blessed November 19th of ’73. the partially integrated hunks of s**t hanging on her Rubenesque frame were rubbed out. now the decision was whether to go with the impact beam behind a Polyurethane skin, or to omit the beam and create a polyurethane bumper with air chambers molded in which promised lower weight and cost. but after a few impact (pendulum) tests in cold conditions, the air chamber design proved to be less flexible than the skin/beam version and allowed for some damage to the built in lights.

by 1975’s end, they were ready to rock and roll. satisfying results with testing meant finalizing designs, approvals, and test molds made to pull pattern shots for final approval to proceed with tooling. Porsche would use Bayflex 101, a PUR-RIM system by Bayer. the PUR-RIM parts would then be painted separately because their drying temperatures of around 90°C were lower than the baking temperatures of the body paint.

artwork for Porsche’s patent application 4231600

the 928 was the first Porsche to have painted PUR body components, this was an important development that revolutionized Porsche’s design and engineering process. by the time the Carrera GT was being designed, engineers and designers were well seasoned on what this new technology could offer, how it could be applied, and manufactured. using PUR-(R)RIM meant small production runs, evolutionary design changes, and future designs could be executed with more flexibility.

a patent application titled Automobile Bumper was filed on October 17th, 1978 and granted as patent number 4,231,600 on November 4th, 1980. Walter Braun, Hermann Burst, and Dietmar Peter were listed as the inventors…these guys along with the rest of the Integrated Bumper project group are the reason that your 928’s nose and a*s still look PERFECT after nearly 40 years. next time you blast by a modern car, think about this little untold moment in history.

put that in your goddamned pipe and smoke it, Artie.


*image sources:,,

**Article republished from

9 responses to Birth of the 928 Integrated Bumper

  1. What a pleasure to read.

  2. The 928 attracts me more every time I see one.
    Are you American, Pablo?

  3. When I see the key picture of this article: bum-per.
    (the world famous German humor)

  4. I enjoyed to read this.
    Good idea, a thorough investigation and a lots of fact-checking.

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