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The Opel Diplomat 5.4 Coupe

A piece I knocked out for an auto enthusiast site on a very rare car – this post garnered a lot of comments and has been linked to by 72 other sites since it was published in 2007. It shows over 1.2 million views so far, and it is still pulling visitors to the original site in very respectable numbers.


I was reading a piece in a European classic car magazine from 2005 (I know, a little late) that featured the Opel Diplomat 5.4, a car completely unknown here in the States, but one of my long-time favorites.

The article was mostly a road test against some other “super-coupes” of the era, and so was short on many of the details that I like most about the Diplomat 5.4 Coupé. Fortunately, since I am a bit obsessive about things like this, I can provide those details.

The first Opel Diplomat V8 Coupé rolled off the assembly line of body maker Karmann in Osnabrück, Germany in the summer of 1965. The top Opel was virtually handmade by the workers at Karmann. Since only 347 of the 5.4 Coupes were ever made, this handmade status would not be a problem in terms of satisifying demand, but it did conspire to drive the high price even higher. The price was approximately 25,000 DM, which at that time would buy you seven Volkswagen Beetles, nicely equipped. The car cost Mercedes-Benz money, but without the Mercedes star and this was a tough sell in Europe. The American-style looks and size (almost 200 inches) were both loved and reviled on the Continent. The car was not a sales success for Opel.

The Opel Diplomat V8 Coupé was the absolute zenith of the Diplomat range and came with a 5.4-liter V8 engine –advertised as the same engine that was used in the Chevrolet Corvette at the time and paired with the GM two-speed automatic transmission, the 230hp V8 engine pushed the Coupé from zero to 100 in under 10 seconds. That was incredibly fast for the era, and gave the Diplomat 5.4 owner bragging rights everywhere he went in Europe. Maximum speed was 206 km/h (125 mph), which was a pretty good top end for a two-speed transmission.

And the interior? I’ll let Opel itself tell you what the interior was like – this is from the company’s press release noting the 40th anniversary of the Opel Diplomat Coupe in 2005: “The top-of-the-line model was characterized by restrained luxury and elegance. The two-door vehicle was equipped with hydraulic steering and braking boost, disk brakes and fog lamps. The interior was dominated by thick carpets, opulent upholstery, real-wood inserts as well as a band speedometer going up to 250 km/h. Power windows, power exterior mirrors and rear foot-well lamps are among the exclusive details the great mass of drivers in Europe would have to wait for quite some time yet.”

Now, here’s something about the Opel Diplomat V8 Coupé that even the few people that know pretty much everything about the cars usually don’t know. Every article written about the car states that the 5.4 liter V8 (known as a 327 small-block V8 here in the U.S.) in the Opel Diplomat is the engine from the then-contemporary Corvette. Owners of the car will tell you the same thing. Even Opel itself makes that statement. Until recently, I too thought this was the case.

An auto enthusiast magazine here on this continent had a retrospective of the Chevrolet small-block V8 in one of it’s past issues from a few years ago (hey, I’ve been busy, OK?), and one of the interesting anecdotes regarding the fabled engine is from the interview with Bob Lutz, currently Vice-Chairman of GM worldwide, and formerly Head of Sales at Opel over 40 years ago when the Diplomat 5.4 was developed. In the interview, he happens to mention the Diplomat 5.4 Coupé and its use of the famous small-block.

Apparently, the small-blocks used in the Opel Diplomat 5.4 are special “endurance racing” versions of the standard Chevrolet small-block engine owing to the fact that the guys at Opel kept burning up the various small-block powerplants (including the standard Corvette engine) sent to them by Chevrolet during the sustained high-speed testing they did for the Diplomat. In order to replicate Autobahn conditions, they ran the cars at a sustained speed of 125 mph for hours on end, and in the process, destroyed quite a few engines. The Opel engineers first went through the stock Chevrolet 5.4 small-block engine, then a special “enhanced” engine that had some Corvette pieces, then the actual Corvette engine, and then were finally sent the “endurance racing” engines which made the grade and thus became the only V8 offered in the Diplomat 5.4 model.

So that’s the engine you got if you had an Opel Diplomat 5.4, and this may also explain why, that although not many Opel Diplomat 5.4 models were produced, you see a fair percentage of the few cars left with very high mileage and still running strong. The Opel Diplomat sort of had a Corvette engine, but not the production engines used in road-going Corvettes – it had the engines used in the Corvettes (and other cars) that did hard-core endurance racing like at Sebring and LeMans. It was a tougher, more durable, higher-revving (and more expensive) small-block V8 than the production Corvette engine, and a better engine all around.

It is unknown how many of the 347 Diplomat Coupes built between 1965 and the end of 1967 survive. One of the remaining ones is in the Opel Museum in Germany. It is a shame it is not driven anymore, but it is there to serve as testament to the grand experiment that Opel launched in 1965.

Many thanks to Karin Loeffler and Klaus Kukwa working on behalf of Adam Opel GmbH, PR, Germany for the photos provided. GmbH.