Mopar A Engines
| A Engine | Years (USA)* | Bore | Stroke |
|---|---|---|---|
| 277 | 1956 | 3.75 | 3.12 |
| 301 | 1957 | 3.91 | 3.12 |
| 303 | 1956-57 | 3.81 | 3.31 |
| 313 | 1957-64 | 3.88 | 3.31 |
| 326 | 1959 (Dodge) | 3.95 | 3.31 |
| 318 | 1957-67 | 3.91 | 3.31 |
The A engine family was a modern, relatively efficient, and durable design produced from 1956 through 1966; its progeny, the LA engine, would start in 1964 and proceed into the 21st Century in various forms. The basic blocks are similarly sized and hard to tell apart from the outside, though the A's polyspherical heads are considerably larger than the LA's heads. Bill Watson wrote:
The A block was fractionally bigger in external dimensions than the LA block, although it was heavier due to the new casting techniques. The LA block 273 weighed 55 pounds less than the poly 318, both used 4.46" bore centres, and both were 21.4" in length, without water pump, crankshaft, etc. The poly heads are much wider and heavier than the LA's wedge heads and that gives the A block engines the appearance of being bigger than the LA engines.
The A engines also went under various trade names, include Red Ram. It was an overhead valve design with dome-shaped heads.
| 1957 Plymouth Figures | 277 | 301 | 318 |
|---|---|---|---|
| Taxable Horsepower | 45 | 49 | 49 |
| Gross Horsepower | 197@4,400 | 215@4,400 | n/l |
| Torque (lb-ft) | 270@2,400 | 285@2,800 | n/l |
| Compression Ratio | 125-165 psi | ||
| Bore x Stroke | 3.75 x 3.125 | 3 29/32 x 3.125 | 3 29/32 x 3 5/16 |
| Compression | 8:1 | 8.5:1 | 9.25:1 |
| Firing Order | 1-8-4-3-6-5-7-2 | ||
Parts interchange: A to LA (Bill Watson)
As for internals, the 273 used the poly (A) 318 crankshaft,
bearings, bearing caps, vibration damper, and conecting rods. The 273
and 318 both had a 3.31" stroke. Pistons were different, though, as the
bores were different while camshafts could not be shared due to the
different valve arrangements.
The sharing of parts was one of the things Chrysler bragged about when the 273 was introduced. But little on the 273 LA was shared with the earlier 277/301. The LA 273 had a longer stroke and smaller bore than the 277/301.
In comparing what was and was not shared, the timing chain of the A was used on the LA. But the early hemis and their poly equivalents (Dodge, DeSoto, Chrysler) and the first Plymouth polys (241, 260, 270) all shared a different timing chain.
Canadian notes (Bill Watson)
The 303 was introduced in Canada before the U.S. Plymouth Fury came on the market. It was used in the Canadian-built 1956 Dodge Custom Royal (2-bbl) and 1956 Chrysler Windsor (4-bbl). In 1957 is was used as the standard V8 in the 118" wheelbase Plymouth and Dodge models.
The 313 V8 appeared in 1957 in the Canadian Custom Royal. For 1958, the 313 became the standard V8 for the 118" wheelbase Plymouth and Dodge models. It was available in Plymouth and Dodge models through 1964, and was replaced by the 318 for 1965. The poly 318 was last used in Canadian production on the 1967 models.
The Canadian 1958 Dodge Custom Royal used the poly version of the 354, shared with the Canadian-built DeSoto Firedome and Chrysler Windsor. Chrysler of Canada did not start using the B block V8 until 1959.
The A engines: 277, 301, 303, 318, 326
(Horsepower figures are gross until 1971.)
Bill Watson noted:
The poly head first appeared in 1956, with Plymouth using a 241 cid version and Dodge using a larger-bored version with 270 cid. In mid-year Plymouth increased the bore of the 241 to 3.56" for 260 cid. Plymouth used the 270 with poly heads in 1956, but replaced it with a new 277 engine, the first A block. It shared little with the Dodge V8 and came only as a poly. The early hemi heads will not fit on the A block.
So, the 303-cid V8 was used, based on the 277 V8 block, with the 3.75" bore replaced by a 3.81" bore. The adoption of the 277 size over the 270 reduced costs - they could share crankshafts and piston rods.
Chrysler also offered a poly head engine in 1955 on the Windsor, using a small bore version of the 331 (3.63" vs 3.81") for 300 cid. The Windsor never came with a hemi engine, using poly heads through 1958.
The A engine was built through 1967, actually, with 1966 being the last year in the U.S. and 1967 in Canada. The US-built 1967 LA 318 has engine number prefix C318 while the Canadian 1967 poly A 318 has engine prefix CC318. (The "C" stands for the 1967 model year while the second "C" for the poly stands for Canada)
Joshua Skinner wrote:
In 1957, the 277 grew to 301 ci with a 3.91" bore and the same 3.12" stroke. Also available beginning in 1957 was 3.91" bore and 3.31" stroke engine netting 318ci. The hottest version of the early A engine was the 1957 Fury 318 with dual quads producing 290 horsepower, the same rating as a 340 6-pack. The lesser versions were rated at 230 hp (318 2v) and 260 hp (318 4v, made from 1958 to 1962). The 1959 Dodge "Red Ram" engine was part of the A family (325 or 326 cid).
Bill Watson noted:
Chrysler produced three different hemis during the 1950s, with different blocks for Dodge, DeSoto, and Chrysler. DeSoto never built a poly engine, although they did use the A-block poly in the export DeSoto Diplomat, the Dodge-based poly in the 1957 DeSoto Firesweep and Chrysler's 354 poly in the Canadian-built 1958 DeSoto Firedome.
We have a more detailed description of these engines - click here.
(Drew Beck reminded us of the 303 V8 used only in the 1956 Plymouth Fury, 240 hp with a four barrel carb; and the Dodge-only 1959 326 V8.)
In 1960, the 318 cubic inch Red Ram V8 produced 230 gross hp at 4,440 rpm, and 340 lb-ft of torque at 2,400 rpm, fed by a two-barrel carb and using a 9:1 compression ratio.
Nicholas Challacombe wrote:
I have a 1962 Bristol 407 with an A type engine of 313cu inches or 5130 cc. It has a four barrel Carter carb 3131s and the engine bore is stated in the work shop manual as 3.875/3.877 inch. These engines came from Canada. Apparently the 318 is a 313 bored out by 30 thou.
All Bristol 407s have the 313 as did all 408s except for the last 18 which had 318. All the Bristol 313s had a perfomance pack and produced 250 hp.
(The photo at the start of this section is the 313, rated at 220 horsepower (gross) in Australian Royals.)
Click here for more on the poly-head engines
(Click here for repair tips | click here for performance tips)
