Mopar A Engines
The A engine family was a modern, efficient, and durable design produced from 1956 through 1966; the LA series of V8 engines was based on a lightweight casting of the A engines, appearing in 1964. The A and LA blocks are similarly sized and hard to tell apart from the outside, but the A's polyspherical heads were considerably larger than the LA's heads.
| 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 blocks were slightly larger than the LA, according to Bill Watson, and considerably heavier. Bore center sizes on the LA 273 and A 318 were identical (4.46”) as were bore lengths (21.4”); but the A engine was 55 pounds heavier. The most clearly visible differences is in the heads: the A engines used poly heads and the LA engines used wedge heads. The polyspherical heads were much wider and heavier.
The A engines shared little with the Hemi-based Poly V8s; since Plymouth’s sales were far larger than Dodge or Chrysler, and pricing was lower, the A-type V8 engines needed to be made far more quickly at the new Mound Road engine plant.
The “single shaft” (Hemi-based) Poly can be identified by its separate valley cover underneath the intake manifold; Randy Hicks wrote that the cylinder heads and intake manifolds were interchangeable with any Hemi engines that had the same deck height. A-series Poly engines did not have the separate valley cover underneath the intake manifold, since the intake itself performed this function. Both series of Poly engines — A-based and Hemi-based — were similar in appearance, with scalloped valve covers and a rear-mounted distributor, despite being from completely different engine families.
The A engines went under trade names including Red Ram. It was an overhead valve design with dome-shaped heads. Dodge wrote, “So durable are they that the standard 25,000 mile laboratory tests for wear had to be changed to 50,000-mile and 100,000-mile checks-because no discernible wear showed up until long past the 25,000-mile figure.”
The A-engines slowly replaced the polyspherical-head (“single-rocker”) V8 engines: 277, 301, 331, and 354. A key difference between the A engines and the older poly engines — essentially, Hemi engines with modified combustion chambers and single rocker arms — was in the ease of manufacturing.
While Dodge, DeSoto, and Chrysler had relatively small sales numbers and could live with the low pace of building the poly V8s, Plymouth’s high production required something cheaper and faster to build. The A engines fulfilled that function, with little, if any, performance penalty. Any loss in performance could be made up in cubic inches, and the A engines ran larger than most of the polys.
| 1957 Plymouth Figures | 277 | 301 | 318 |
|---|---|---|---|
| Gross Horsepower | 197@4,400 | 215@4,400 | n/l |
| Torque (lb-ft) | 270@2,400 | 285@2,800 | n/l |
| Compression | 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 | ||
Bill Watson noted that the LA-based 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, though little on the 273 was shared with the earlier 277/301 A-engines.
| 1962 318 figures | 318 truck | 318 2-barrel | 318 4-barrel |
|---|---|---|---|
| Gross Horsepower | 200, 202 | 230@4,400 | 260@4,400 |
| Torque (lb-ft) | 286/288@2,400 | ||
| Compression | 9.0 | 9.0 |
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)
| 1960 318 vs GM and Ford |
Ford 292 | Dodge Red Ram 318 | Chevrolet 283 |
|---|---|---|---|
| 185 hp | 230 hp | 170 hp | |
| 292 lb-ft | 340 lb-ft | 275 lb-ft |
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.
| 1960 Dodge Figures | 277 | 301 | 318 |
|---|---|---|---|
| Gross Horsepower | 197@4,400 | 215@4,400 | 230 |
| Torque (lb-ft) | 270@2,400 | 285@2,800 | 340 |
| Compression | 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 | ||
(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.)
Poly-head engines: 277, 301, 331, 354
| Model | IBP-4002 |
| Rotation | Clockwise |
| Advance Control | Automatic |
| Point Gap | .015 to .018" |
| Breaker Arm Spring Tension | 17 to 20 |
| Contact Dwell (degrees) | 29 to 32 deg |
| Automatic Advance curve (Distributor speed) | |
| 290 to 410 | 0 Deg |
| 410 | 0 to 2 Deg |
| 650 | 4 to 6 Deg |
| 1650 | 8 to 10 Deg |
| Vacuum Advance Curve: Manifold vacuum in inches of mercury | |
| 6.1 to 7.3 | 0 Deg |
| 10 | 4.6 to 6.6 Deg |
| 14 | 10 to 12 deg |
| Condenser Capacity (Microfarads) | .25 to .285 |
| Timing Mark location (marks 2 deg apart) | Fan Drive Pulley |
| Engine Idle Speed (RPM) | 475 to 500 |
| Firing Order | 1-8-4-3-6-5-7-2 |