To start at the beginning with Chryco (Canadian) engines, one has to go back to the early 1930s.
In 1930-31, the Conservative government of Richard B. Bennett instituted an auto import duty scheme based upon the Canadian value of the car sold in Canada, including labour. The higher the "Canadian" content, the lower the import duties on the imported parts. Thus, Chrysler of Canada could import engines, transmissions and the like with lower duties as they built their own bodies and used Canadian suppliers for rubber parts, upholstery, brakes, ignition parts, etc.
In 1935 the Conservatives were defeated and during 1936 the new Liberal government under William Lyon Mackenzie King reverted back to the old policy of a flat duty across the board, on all parts imported. For 1937, Chrysler of Canada built only 6-cylinder cars and imported all 8-cylinder cars, convertibles and some long-wheelbase models. Later, the Hayes-body coupes, the Town & Country, and the 1940s Town Sedan would also be imported and not built in Canada.
Chrysler of Canada made the decision to build an engine plant in Windsor, Ontario, in 1937, but due to market size, build only one engine block. They choose to build the so-called 25" block, with its 3-3/8" bore, and simply change the stroke (crankshaft and connecting rods) to adjust the engine size. It was possible to take the 3-3/8" bore block and make a smaller engine (it got down to 201-cid), but the smaller block could not be enlarged to 240-cid or larger, as the larger block could, and did, getting up to 264.5-cid.
Thus, an American-built car could have a 217.8-cid (3.25"x4.375") engine while the Canadian equivalent had a 218.0-cid engine (3.375"x3.75"). As to the difference in market, consider 1938 model year production -
The decision to go with the larger flathead six was one made out of economic necessity. Chrysler of Canada just did not have the market to support production of two engine block sizes. Similarly, Ford of Canada produced flathead V-8 engines up to 1954, the same block used for all Ford of Canada products. The Ford and Meteor did not get a 6-cylinder engine until mid-1956, and even then the engine was imported. Although the ohv V8 was introduced in Mercury and Monarch for 1954, Ford and Meteor would not get it until 1955.
General Motors used the Chevrolet engine in Pontiacs for many years. The Canadian-built Pontiac did use the American flathead six from 1940 to 1954. All the other G.M. lines used imported engines, including Pontiac straight-eights, in the years they were built in Canada. But General Motors was a much larger company, even in Canada, especially after World War II.
In 1951 Chrysler of Canada began importing V-8 engines for the Canadian-built Chrysler Saratoga. The DeSoto FireDome V8 engine was imported starting in 1952 and the Dodge V8 in 1953. When Plymouth came out with its V8 for 1955, that engine was imported for the Plymouth Belvidere and Dodge Mayfair. The lower-priced Plaza, Savoy, Crusader and Regent all remained 6-cylinder only. Thus the V-8 engines offered in Canada from 1951 to 1955 were identical to the American firm, as the engines were built in Detroit.
During 1955 Chrysler of Canada underwent an expansion program, building a new V-8 engine plant, expanding the Windsor assembly plant and building a string of parts depots across the country as the firm ended the old area distributor network and had dealers connect directly to Chrysler.
For the 1956 model year, Chrysler of Canada began building V-8 engines for the Canadian market. The Plymouth and Dodge used, first, the 270-cid V8 then switched to the 277-cid V-8. The 303-cid V8 shared much with the 277-cid V8, including the heads, and had a 3.81" bore and 3.31" stroke, compared to the 277-cid's 3.625"x3.25". It was used in Canadian-built Dodge Custom Royal and Chrysler Windsor models. Also, the engine was exported to Detroit for use in the Plymouth Fury, and no, it was not available in Canadian-built Plymouths or 115"-wheelbase Dodges in 1956.
And here lies Chrysler Canada's problem - that larger Dodge. The American Ford company built Ford, Mercury and Lincoln. The Ford went against Chevrolet and Plymouth, the Mercury against Oldsmobile and DeSoto, and the Lincoln against Cadillac and Imperial. General Motors also had the Pontiac and Buick, with Pontiac going against the Dodge and Buick against Chrysler.
The larger Dodge was not a big seller, with 2,650 produced for 1954 model year, 3,650 in 1955, 7,000 in 1956, 7,048 in 1957, and 4,345 in 1958. If Chrysler had imported the Custom Royal, the 303 and 313 may very well have not come about. Instead, Chrysler Canada could have followed the American Plymouth engine development.
The 313-cid V8 was derived by boring out the 303-cid V8. Both had a 3.31" stroke, but the 313 had a 3.875" bore compared to the 3.81" of the 303. The 313 was introduced in 1957 for the Dodge Custom Royal, while the smaller Dodges and Plymouths got the 303. For 1958, the 313 V8 moved down to the small Dodges and Plymouths while the Canadian-built Dodge Custom Royal went to the 325-cid V8.
In the same years in the U.S., Plymouth used the 277-cid V8 in 1956 and again in 1957 for the Plaza. By enlarging the bore from 3.75" to 3.91", Plymouth got the 301-cid V8, used in all but the Fury in 1957. The Fury used the 318-cid which was the 301 stroked to 3.31". In 1958, the 318-cid V8 was used by all Plymouth V8 models, with a 350-cid ("B" block) optional.
To save money, Chrysler of Canada kept the 313 instead of boring the block out to 3.91" for 318-cid. The extra 5-cid just was not worth the expenditure, I suppose. Both engines had an advertised 225 horsepower. Chrysler was also facing a shrinking market at this time. In 1955 calendar year Chrysler of Canada produced 97,444 cars, which fell to 91,119 in 1956, 69,421 in 1957, 44,131 in 1958 and 42,618 in 1959. The "Forward Look" of 1957 may have sold like hotcakes in the States, but in Canada it bombed.
Remember, Chrysler of Canada built its own "A" series engines, from blocks to cranks to pistons to heads to camshafts. This was the result of the new V-8 plant opening in late 1955. The switch to the 318-cid for 1965 was made in anticipation of the Canada-US auto trade agreement. Also, Chrysler of Canada did not begin production of the new thin-wall, wedge-head "LA" engine until 1968 model year, one year after the U.S. parent did. Something to watch out for when restoring a 1967 Plymouth Fury or Dodge Polara/Monaco model. Chrysler of Canada continued to build the slant-six and the 318-cid V-8 into the very early 1980s. The engine plant was closed, along with the old Maxwell-Chalmers plant on Tecumseh Avenue, as cost-cutting measures to save the company from bankruptcy.
As to the 1955 Chrysler Windsor 301-cid Spitfire V-8, it is actually a small-bore poly-head version of the 331-cid hemi V-8. The two engines shared crankshaft, oil pan, timing chain, timing chain cover, camshaft, and connecting rods, to mention a few bits. Pistons, heads and manifolds were different, of course. The engine was offered in both Canadian and American built 1955 Chrysler Windsor models, and Chrysler of Canada imported the engine.
As to why the 1955 Chrysler Windsor 301 seems smaller than the 1956 Dodge Custom Royal 303, it may be an optical illusion. Although the big American-style Dodge shared bodies with Chrysler from 1941 to 1952, and again from 1957, the 1953 to 1956 Dodge bodies were shared with Plymouth. To compare, the overall width of the 1956 Chrysler was 78.8" with a 60.4" front tread, The 1956 Custom Royal was 74.6" wide with a 58.9" front tread. So the engine compartment on the Dodge was undoubtedly narrower than on the Chrysler. Only a tape measure could tell for certain, though.
Convertibles were not a large seller from the 1930s through to the early 1960s. From 1948 to 1951, due to government currency restrictions, Canadians could import a convertible from the U.S. only with government approval. The first Plymouth-based Dodge convertible sold in Canada was the 1954 Mayfair. By my computations, only about 179 were imported.
Chrysler of Canada began building convertibles in 1963, and built 108 6-cylinder 440 series convertibles and 318 V-8 convertibles, still very small potatoes. Although the American Dodge for 1963 was available as 330/440/Polara, the Canadian Dodge was 220/330/440 with no Polara series.
The term "Chryco" was used by Chrysler of Canada for its parts department from the 1930s into the 1970s. The more the Canadian market was integrated with the American, the more the name "Mopar" was used in Canada. At the same time, the "Autopar" name disappeared. It was used by Chrysler of Canada for its line of parts for non-Chrysler dealers, much like Prestolite, Champion, and the like. Chrysler offered everything from ignition parts, hoses, brake parts to tires under the "Autopar" name.
Myself, I refer to my 1962 and 1965 Valiants as "Chrycos". My 1965 Valiant Owners' Manual and Accessories Catalogue refer to Chryco parts, and not Mopar. My old 1978 Aspen and Monaco Brougham coupes, though, were Mopars.
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