Polyspherical Engine
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Introduction

    Older style 277-301-318 engines are called A engines.  They were produced from 1956 to 1966.  The 'LA' engine was introduced in 1967 and is still produced today.  This has led to some confusion with the added popularity of the newer 'LA' engines, also called 'A' engines.  The two engine families are closely related, but their parts are not completely interchangeable.  To avoid confusion, it is best to refer to the earlier engines as the "old style" engine series.

    The old style engine series is not very popular with hot rodders and performance enthusiasts because of the lack of performance parts.  The most popular hot rod items such as headers, camshafts, intake manifolds, and cylinder heads (like the W2) that are available for the 318-340-360 are not for the old style engines (but if you know where to look and look hard enough you can find these parts)
    The old style 'A' engine was introduced in 1956 as a 277 cubic inch engine with 187 hp standard.  The 301 and 318 engines were introduced in 1957.  The 318-2bbl has 230 hp while the 4 bbl had 260 hp.  Which was the higher output for the old style 'A' engine.

Block

    The bellhousing bolt pattern on the rear of the block is the same on all 'A' engines, including the 1964-present 'LA' engines.  The old style engines use two engine mount brackets (left and right) that are the same, while the newer 'LA' engines have a left and right bracket.
 
 

Year
Engine
Bore x Stroke
1956
277
3.74'' x 3.12''
1957
301
3.91'' x 3.12''
1957-1966
318
3.91'' x 3.21''

Crankshaft

    It is interesting to note that the main journal diameter of the 277-301-318 family is 2.50", and the rod bearing diameter is 2.12" both the same as the newer model (273-318-340) engines.  The new series 318-360 "sleeved" if it is extremely worn and stock pistons are to be used.  The vibration damper timing tape can be used on all old style 'A' engines.  The 1/2" hardened head bolt washers (P4120459) can be used.  However, the old style engine used a different head gasket than the newer engines.  The timing chain and sprockets are interchangeable.  The roller timing chain sprocket set is P4120262.

Cylinder Head

    The 277-318 old style cylinder head is generally called a poly-sphere.  Looking at the strange valve angle it appears to be a modified Hemi.  It certainly isn't a wedge.  The casting number is 2268341.  Analyzing these cylinder head port shapes and valve angles today we'd call this head a semi-hemi or a canted valve.  These style heads are very popular in racing today, they are made by the other manufacturers.  But these other engines didn't exist in 1957 when the canted valve 318 was introduced.  They weren't brought out until the mid 60's.  The old style 318 was years ahead of it's time.  The cylinder heads and valve covers are not interchangeable with the new engines and serve as the best way to identify the two engine groups.  The two families of engines the old style (277-301-318) and the newer 'LA' engines (273-318-340) can be identified (one or the other) by the valve location.  The 'LA' family (273-360) has the valves located all on one side.  The older style valve covers are attached by two bolts in the middle ends of the valve cover.  The newer 'LA' engines use five small screws around the outside of the cover.

Camshaft and Valve Gear

    Old style 'A' engines use the same 1.685'' valve spring installed height as the 340-360.  The best performance spring is P4120249  for camshafts up to .500'' lift for race camshafts up to .640'' lift valve spring P3412068 is the best.  With this race spring, a titanium retainer (P4007178 should be used.  For general high performance applications using the P4120249 valve spring, Viton Valve seals (P4120492) are recommended.  To centerline the camshaft, the offset key package (P7286500) is required.  Old style 'A' engine rocker arms are different for the newer 'LA' group.

Oiling System

    The oil-pump distributor drive shafts are the same.  For high performance application, the heavy duty shaft with hardened tip (P3690715) should be used.

Induction System

    The factory performance options were rather limited for this engine family although the 4-bbl Carburetor and manifold were used on the 318 up to 1962.  It was rated at 260 hp.  Since then it has only been used as a 2-bbl.  There is also a 4-bbl manifold available from Weiand for this engine, since the original piece may be hard to obtain.  The 8-bbl manifold is even more rare  and would be next to impossible to obtain.  Edelbrock even at one time made a six bbl manifold for these engines that use three old 50's style Ford carbs.  these manifolds are even rarer.

Engine Assembly

The old style 318 blueprint specs are as follows:
 

Year Engine Headcc Deck Height
65-66 318 70.6 .012'' Above Block
64 318 71.6 .003'' Above Block
63 318 71.6 .012'' Above Block
62 318 2-bbl 73.6 .003'' Above Block
62 318 4-bbl 66.5 .003'' Above Block
60-61 318 all 71.6 .003'' Above Block
Old Style 273-301-318 'A' Engine Torque Specs.
 
 
Part
Foot Pounds
Inch Pounds
Connecting Rod Nut-Plain
45
-
Cylinder Head Bolt
85
-
Main Bearing Cap
85
-
Camshaft Nut
125
-
Camshaft Lockbolt
35
-
Camshaft Thrust Plate
-
210
Chain Housing Bolt
30
-
Clutch Housing Vent Hole
-
100
Clutch Housing Pan Drain Plug
35
-
Crankcase Vent Outlet Pipe
-
15
Crankshaft Bolt
135
-
Cylinder Head Cover
-
36
Engine Front Mounting
    To Engine Bosses
    To Frame
    To Frame Bracket Stud
45
85
20
-
-
-
Engine Rear Mounting
    To Transmission
    To Frame
35
35
-
-
Flywheel Housing to Cylinder Block
50
-
Flywheel Housing Cover
-
100
Intake Manifold
30
-
Oil Level Indicator Tube Bracket
-
130
Oil Pan Drain Plug
35
-
Oil Pan Bolt
15
-
Oil Pump Cover Bolt
15
-
Oil Pump Attaching Bolt
35
-
Oil Filter Base Attaching Bolt
30
-
Oil Filter Cover Bolt
30
-
Oil Filter Tube
30
-
Rocker Shaft
27
-
Valve Tappet Cover
-
50
Vibration Damper Bolt
-
200
All information is obtained the Mopar Performance book "Engines".

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