Chariot of Fire

Back in 1973, AMG inserted a might M100 V-8 engine and transmission into the elegant 1966 300SE Cabriolet – with spectacular results

Article Gary Anderson, Terry Price

Images Terry Price

Spotting a unicorn at a Concours d’Elegance is always exciting. In this case – at a small local concours on the lawn of the Grizzly Peak Winery in Ashland, Oregon – what caught my eye was a strikingly handsome 300SE Cabriolet from the late 1960s with a stunning red leather and Macassar wood interior. But what was truly startling was seeing the German-style license plate on the front bumper that read “300SE AMG” and the 6.3-liter M100 V-8 engine completely filling the space under the hood. I had never even heard of a W112 Cabriolet fitted with an M100 engine, but here was one parked right in front of me.

One of a kind

Not sure what I was looking at, I called over veteran Mercedes-Benz expert and all-round automotive adventurer Blue Nelson, who also happened to be looking over the show field (see “Blue’s Byways” beginning on page 51). Carefully noting the neat details of all the work that had been done to install the M100 engine into the 300SE Cabriolet, we agreed that the details of relays, wiring and hoses employed to insert the big engine definitely indicated the job was done around 1971 when two young engine builders named Erhard Melcher and Hans-Werner Aufrecht were successfully racing a Mercedes-Benz 300SEL 6.3 powered by M100 engine. Their fierce machine had been dubbed the Red Sow by an awed press and public. But the Red Sow was a sedan and this was a Cabriolet. What was the connection?

Finding the 300SE Cabriolet’s owner, Terry Price of Legendary Motorcars, I quickly learned the briefest outline of the car’s rich history. The engine swap had in fact been done in 1973 in Burgstall, Germany, before Aufrecht and Melcher moved their fledgling operation to Affalterbach and began making a name for the little company they would call AMG. Price said he thought it might be the only 300SE Cabriolet like it in the world. I promised him that we would link up again so that I could find out more of the details about this seemingly unique vehicle and do a story to appear in the pages of The Star.

A blown engine started it all

The story began in the early 1970s with a young American Mercedes-Benz enthusiast named Karl Middlehauve who had just purchased a used Mercedes-Benz 300SE Coupe in Nurnberg. However, the engine blew even before he and his wife got to the seaport at Bremerhaven. With AMG 6.3 engines costing less than a rebuild of the 3-liter engine, Middlehauve had the Coupe transported to the AMG workshop. There, engine magicians Aufrecht and Melcher replaced the Coupe’s three-liter engine and automatic transmission with a 6.3-liter drivetrain based on those being installed at the time by Mercedes-Benz into the Grand 600s and 300SEL 6.3 sedans.

That modified 300SE Coupe proved to be such a dream – powerful and responsive as well as elegant – that Middlehauve immediately began looking for a 300SE Cabriolet that he could have re-engineered in the same manner. Finally, in 1973 Middlehauve found just the car he had been looking for, a silver 300SE Cabriolet with red leather interior. The vehicle was in excellent condition, with only about 42,000 miles on the odometer, but with an already tired drivetrain. Deal done, the Cabriolet was soon on its way to AMG in Germany for the same treatment as his Coupe.

Based on the carefully maintained records documenting the Cabriolet, AMG had installed a new 6.3-liter engine that was tweaked to what at the time the little company called “Stage 2 Tuning.”  That upped the output of the M100 engine from 300 to 325 horsepower; torque grew from an already substantial 434 pound-feet to a stump-pulling 500 pound-feet – not at quite the racing-on-the-bleeding-edge level of the powerplant in the famous Red Sow, but close enough.

Instead of retaining the 300SE’s stock 4-speed automatic transmission with fluid coupling, the new 6.3-liter engine was mated to a ZF five-speed floor-shift manual transmission, a sturdy box also in use by Aston-Martin during the same period. Of course, the original differential was replaced with a standard 6.3 rear-end to prevent catastrophic metal-shredding failure; the version supplied stock with the 300SE would never have been able to handle the revitalized vehicle’s massive new amount of torque.

The middle of the story

Through the years, Middlehauve’s business, Classic Car Restoration in Wausau, Wisconsin, flourished. He and Terry Price, also in the automobile business, got to know each other. Around 1999, Price became aware of the W112 Cabriolet. By that time, the drop top had been sitting for a while, and had only accumulated an additional 10,000 miles.

In 2015, Middlehauve finally decided to sell the 300SE 6.3, but another buyer managed to grab it, paying a price comfortably north of $300,000. However, finding that the car was barely drivable, with no clutch or brakes, the buyer reneged on the deal. Middlehauve then turned the cabriolet over to Stu Carpenter of Copley Motorcars to find a buyer. This time Price was ready. He quickly made a successful offer for the car.

Not restored, refreshed

Price was undeterred by the problems with the clutch and brakes that had scared off the first buyer. Because AMG’s installation of the complex drivetrain means that the engine must be removed to replace the clutch, Price took the opportunity to have his shop go through the M100 thoroughly. He replaced all the hoses and gaskets, and checked all clearances and specifications. Price also cleaned and plated, polished or painted every mechanical component. The engine itself is now a work of art that runs like a fine watch.

On the interior, the original Macassar wood trim – which had never been out of the car – was simply cleaned and waxed. As part of the refurbishment, a few extraneous AMG plaques accrued through the vehicle’s long life were removed. However, a plaque that covered the vacant gear indicator window left behind by the original automatic transmission was left in place, as was an auxiliary instrument panel.

On the other hand, the cabriolet’s factory leather upholstery had some issues. Though the leather itself was generally in good shape and would respond well to soaking in collagen hide food, thread in the seams had aged and split in a number of difference places, and there were some worn panels on the bolsters and other areas. Price’s solution was straightforward. He managed to procure a good Roser hide from another respected restorer, already dyed in the same red color of the rest of the interior. Using that to replace the worn panels, a trim specialist re-sewed all the interior panels and installed them over redone padding and horsehair in the same manner as the original seats and panels.

The exterior paint, which had been redone at the time of the original M100 engine installation in Burgstall, responded well to careful detailing. At the same time, all chrome was removed and replated, as were all fasteners.

When we first saw the car, it sported a set of chrome-plated wheels that Middelhauve had added when he owned the car. Recently Price was successful in finding a set of wheels that would have been appropriate to the car when it was first produced. This new set of wheels presented the perfect opportunity to add a subtle nod to AMG‘s heritage. To each wheel, Price added the insignia adopted at the time of the merger between AMG and Mercedes-Benz. A brand-new stainless steel exhaust system was also plumbed in, finished with a dual exhaust outlet similar to that which would have been stock on the 300SEL 6.3.

All together, Price estimates that reconditioning the 300SE AMG required about 1,000 hours. Combining the purchase price of the car and the refurbishment costs, Price’s total investment in the cabriolet might be greater than what it could fetch in the open market. However, he has received attractive offers well in excess of current transaction prices for 300SE Cabriolets or 300SEL 6.3 sedans in similar condition.

But this calculation is irrelevant to Price. In his view, the value of such a one-of-a-kind Mercedes-Benz – one that could have and perhaps even should have been built by the factory in its period – is priceless.

What about the future?

Price finds the true value of his 300SE AMG Cabriolet when he is behind the wheel. Driving the car on the scenic back roads of far northern California and through the Rogue Valley of southern Oregon, Price reports that the air suspension really comes into its own, steadying the vehicle through the curves and smoothing out any roughness in the pavement. Of course, the Cabriolet’s power and torque make it delightfully responsive to any prod of the accelerator to summon speed on the open road or power out of tight corners.

All this performance combined with the classic Cabriolet’s exceptional visual impact makes for a heady automotive mix. Price looks forward eagerly to driving this stunning 300SE AMG to car shows and on tours along the West Coast. We can’t wait until we see this extraordinary Mercedes-Benz on the show field once again and, when circumstances permit, slip into the luxurious interior for an open-air drive.

Captions

A total of 28,918 Coupes and 7,013 Cabriolets in the W111-W112 range were built 1961-1971.

This W112 300SE cabriolet was the most exclusive model; only 708 examples were made.

Underscoring the Cabriolet’s long and luxurious stance, chrome trim extends from headlights to taillights and prominent chrome trim elements top both front and rear wheel arches.

The gleaming M100 engine shoehorned into the 300SE’s engine compartment.

The brand-new stainless steel exhaust system with 6.3-style tips;

Custom touch of AMG badging on hub covers of period-correct wheels;

Grille badges celebrate vehicle’s heritage;

The opulent red leather interior positively glows with sporty luxury.

Concerto in chrome: This 1966 300SE cabriolet’s massive yet elegant front end – with its show-stopping grille, lights and cascading bumper – makes an indelible visual impression.

The leather is resewn but all original; the Macassar wood has never been restored. An auxiliary gauge panel was added after the new engine was installed; the manual gear shift links to a ZF 5-speed transmission added when AMG installed the engine.

Specifications

1966 Mercedes-Benz 300SE Cabriolet (W112)

 AMG-installed M100 Engine

TYPE: Two-door cabriolet

ENGINE: M100 V-8 with Bosch mechanical fuel injection

with 2 single overhead cams • 5 main bearings

BORE & STROKE: 4.06x3.74 • DISPLACEMENT: 6,332cc

HORSEPOWER: 325@ 4,100 rpm (AMG Stage 2)

TORQUE: 500 lb-ft @ 3,000 rpm (AMG Stage 2)

TRANSMISSION:

ZF Five-speed (shared with Aston-Martin) • 6.3 liter differential

SUSPENSION:

All-wheel independent air suspension • front and rear disc brakes