The C300C Hemi Engine (C76-300)
The C300 engine powered the sport-luxury Chrysler 300C, getting 375 to 390 gross horsepower from 392 cubic inches - in 1957 and 1958. (Torque was a full 420-430 lb-ft.) Serial numbers on these engines started with NE57-1001, but those numbers are shared with a milder 325 horsepower version. This was a 90 degree V8 fitted with two four-barrel carburetors. The basic engine design was similar to the poly head V8s. Some C300 unique features include pistons made of tin-coated aluminum alloy rather than cast aluminum. The only car to get the C300 engine was the Chrysler 300C.
The C300 was of the same family as the Fire Power V8s. It is essentially a bored and stroked 354 Hemi at heart. One interesting note is the fact that this "early Hemi" engine family was Chrysler's first series of V8 engines - they started out with the Hemi, and then developed the polyspherical head versions to save money. The Hemis had large valves for good flow, room for cooling around the exhaust valves, and opposing valve placement, again for good airflow. One advantage of the Hemi other than efficiency and flow was the ability to run very high compression ratios for the time. These engines were shared across all divisions, in different forms (bore, stroke, carburetion, etc). The series was introduced in 1951 and retired rather quickly in 1958 due to expense and weight issues.
Connecting rod bushing was steel-backed bronze, with interchangeability listed as "all."
The camshaft was a chain drive with five steel-backed babbit bearings, and thrust taken by a thrust plate. The timing chain was non-adjustable with 68 links, a pitch of .375", and a width of 1 1/8". The engine used mechanical tappets, horizontal slot with steel strut pistons made of tin-coated aluminum alloy and weighing 700 grams. The piston pins were full floating, offset toward the right of the engine. Each piston had three rings - two for compression, one for oil.
Intake valves were made of silicon chromium steel, with a 2" head and 5.031" length to the top of the valve face. Adjustment was at the rocker arm. The seat angle was 45 degrees. Exhaust valves were nickel treated manganese - chromium nickel steel with a 1.75" head diameter and 4.990" length, again adjusted at the rocker arm. There were 16 outer valve springs, 16 inner valve springs.
The heads had hemispherical combustion chambers - no surprise since it's a Hemi - with iron alloy valve seat inserts.
A rotary full pressure oil pump was used, driven by the camshaft and maintaining 40 to 65 pounds of pressure from 40 to 50 mph. A clogged filter could drop that 15-20 pounds.
Our source wrote: "The 392 hemi spec sheet is different than one in service manual, as it is for solid tappet '300' engine, not hydraulic Imperial engine. The 1957 service manual doesn't have info for solid tappet engine, only hydraulic."
|Bore and Stroke||4.00" x 3.90"||Compression Ratio||9.25:1|
|Compression Pressure at 150 rpm (plugs removed, wide open throttle)||150 to 180 lb||Maximum variation between cylinders||20 lb|
|Cylinder numbering (front front of engine): left bank||1-3-5-7||Right bank||2-4-6-8|
|Fully counter-balanced, with tri-metal bearings||Journal diameter||2.687 to 2.688|
|Crank pin diameter||2.374 to 2.375||Maximum out of round permissible||.001"|
|Main bearings||5||Desired diameter clearance||.001 to .0025"|
|End play||.002" to .007"||Maximum allowable before reconditioning||.010"|
|Thrust taken by||#4 main bearing||Finish at rear seal surface||Diagonal knurling|
|Interchangeability of bearings: upper and lower||1, 2, 4
|Upper and lower #5 not interchangeable|
Connecting rods and bearings
|Drop forged I beam, length:||6.951||Weight (less bearings)||27.6 oz|
|Bearings||Tri-metal||Diameter and length||2.375 x 7/8|
|Diametral clearance desired||.0005" to .002"||Maximum allowable before reconditioning, side clearance||.0025", .006 to .014"|