Automotive History: Diesel Chrysler Slant-Sixes, In-House and Otherwise

Lately it’s Diesel Days here at CC. Paul’s put up articles about a gasoline-engine-based diesel that went just fine (VW’s 4-pot), and one that probably shouldn’t have been built but was (GM’s Oldsmobile V8). Now here’s a kind that maybe should’ve been built, but wasn’t: a diesel version of Chrysler’s 225 Slant-Six.

Actually, it’s not just one but three diesel versions of the Slant-Six, none of which was commercialised. Two of them were engineering programs in-house at Chrysler. Bill Weertman—Chrysler’s Engine Design Managing Engineer 1955-’62; Engine Design & Development Assistant Chief Engineer 1962-’76; and Chief Engine Engineer, 1976-’87—says:

“Chrysler Engineering had a major program to develop a diesel version of the Slant-Six engine. The program started in 1975. The first design effort resulted in a design of a diesel cylinder head, manifolding and piston with few changes to the lower end of the 225 engine. The engine was naturally aspirated and utilized an Indirect Injection (IDI) combustion chamber which was in common usage on automotive type diesel engines. A number of engines of this type were built and run. The program was not a high priority and was interrupted at times due to higher priority work.

“In 1980 the program was given a sudden boost in status due to the appearance of a number of competitive diesel powered passenger cars on the market and continued concern about availability of fuel supplies. At this time, the program was changed to add turbocharging and to add a 2.2L 4-cylinder derivative engine (also turbocharged) to power the front-wheel-drive vehicles.

“The extra loading caused by the turbocharging required that the crankshaft and crankcase be redesigned to provide 7 main bearings for the six cylinder engine and 5 main bearings for the 4 cylinder engine. The engine was essentially totally redesigned to give it the best diesel technology available.

“To make the diesel program more viable from a business standpoint, a joint venture was formed with an outside diesel engine company. With both Chrysler’s use of the engines in passenger cars and trucks and the outside company’s sales of the engines, a higher production volume of engines would result with inherently better economic operation of the plant.

“Windsor [Ontario] Engine Plant was designated to be the source of the engines. Prototypes were built and testing was in process on dynamometers and in vehicles when the entire diesel program was cancelled in 1983. The cancellation was based on the sudden drop in demand for passenger car diesel power with the passing of the oil crisis problem that started in 1973 and lasted through about 1982.”

Weertman recalled that he went test-driving with Lee Iacocca in a Dodge pickup truck equipped with the turbo diesel 225. It performed well, but Iacocca decided there wasn’t enough market interest in small diesel engines to justify series production. Too, Iacocca might have been spooked to some degree by the GM debacle. Was cancelling this engine the right decision? We in this timeline will never know for sure. The hot and cold running corporate funding and favour is evident in four Popular Science clips; first from June of 1979:

…then May of 1980:

…then November of 1981 (we learn the identity of the “outside diesel engine company” Weertman mentioned; was there any doubt?):

…and November of 1982:

Weertman says the five or six engines that were being tested at the time of program cancellation were put in storage and later sent to the Chrysler Historical Collection where they still resided as of 2006. But that’s one of the prototypes at the top of this article, and it looks to be in somebody’s private garage; one way or another some of them appear to have escaped the corral. These things happen; six years ago somebody reported encountering a stash of the prototype 225 turbo diesel engines said to have been saved from a scrapyard; perhaps this in the pic is one of those.

And various parts of these engines are floating around, too. I found this exhaust manifold and subsequent-casting-number parts on eBay close to 15 years ago:

When I showed Weertman these photos, he said “I am certain it is the manifold of the turbocharged diesel version of the Slant Six engine; the cross-section [drawing] of the engine displays the exhaust manifold in situ. Just before its abrupt termination in 1983 the program was on a path to go into production, which would account for the manifold having a cast-on part number and pentastar. Since there was a multitude of stockroom parts it is not surprising that a wayward exhaust manifold has appeared on the ‘outside’.”

Here are more bolt-on parts spotted in the wild:

Alright, so that covers, to the best of my ability, Chrysler’s own R&D work on a diesel Slant-Six. But wait, there’s more! A British outfit called Ricardo Consulting Engineers (apparently still a going concern, and a major one at that) published a paper in 1981, “A Passenger Car Diesel Engine For America”, presenting great detail on the development of a diesel version of the 225 Slant-Six. How separate or integral Ricardo’s work was to Chrysler’s is not explicitly specified, but my take is that this was a more or less parallel project: overlapping timeframe, different companies. There’s a lot to be learnt by reading it, such as the power and emissions effects of injection timing, and deliberate exhaust backpressure to improve heater performance. In the end they wound up with a non-turbocharged engine giving almost identical horsepower and torque to the gasoline-fired 225 with single-barrel carburetor, with much better fuel economy and lower emissions. Click the front page here to obtain the whole report (PDF), which contains extensive real-engine test data:

The 225-1v engine was getting wheezier and weaker by the year in the late ’70s, but it still (barely) made 3-digit horsepower, and matching that with a naturally-aspirated diesel—probably with better driveability—was quite a nice achievement that raises questions of what thoughtful, dedicated development of the turbocharged engine might have accomplished.

(there were some diesel-powered Darts and Valiants. They’re outside the scope of this article, though, so we’ll save ’em for another day.)