303 CID Engine Detail

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General Information

Note: The information contained in all of the "Engine Detail" sections should be read before proceeding with modifications, etc., because some information that applies to all engines, or all small blocks or all big blocks, might not be duplicated in every section.

For the 1949 model year Oldsmobile introduced the Rocket V-8 engine. This was a truly revolutionary development for those times. To help put this engine in perspective, Ford was the recognized "fast car" with its flathead V-8 engines. No other affordable car of the day could approach Fords performance potential. The Ford V-8 engines of the day were rated at 100 horsepower and they had at least 15 years of development to get there. The new Oldsmobile Rocket engine was rated at 135 horsepower, a 35% increase!!

This new engine incorporated a number of unique designs all with the idea of raising the compression ratio from the days standard of approximately 6:1 to an eventual 12:1. The Rocket engine never reached the 12:1 goal, but but it's offspring came very close. The new engine combined for the first time (excluding the almost simultaneous introduction of the similar Cadillac engine) a 90 degree V-8 with overhead valves and slipper pistons. This Rocket had 303 cubic inches, a 7.25:1 compression ratio, two barrel carb and could produce 135 hp at 3600 rpm, and 263 lb-ft of torque at 1800 rpm.

Interestingly, Oldsmobile didn't have a standard transmission that they felt could stand the torque of this new engine, so Hydra-matic was the only transmission choice for the 1949 Rockets. In 1950 Olds raided Cadillacs parts bins and used their standard 3-speed, a transmission that had an excellent reputation among hot rodders of the time. 1951 and on Olds used a "selector-type" 3-speed transmission that is considered much inferior to the 1950 units.

The 303 engine has earned a reputation as being remarkably trouble free. With proper maintanence the engine should give 100,000 miles with little trouble. Heads and blocks just didn't seem to ever crack, these engines were way over engineered! Some have described this engine as an early, indestructable, version of the small block Chevy. That descripition is not entirely correct however, actually the Chevy engine was an updated version of this engine!

The 303 engine was used in various forms from 1949 to the 1953 model year, and in 1954 the engine was enlarged to 324 cubic inches. This was a result of increasing the bore from 3 3/4 inches to 3 7/8 inches. The engine was again enlarged in 1957 to 371 cubic inches and again to its final size of 394 cubic inches in 1959.

Any engine from 1949 thru 1958 will bolt into a 1949 to 1953 body without much trouble. Olds did go to 12 volt electrics in 1953, so that would likely be the biggest problem area in swapping these engines. Car equipped with the 303 and power steering used different intake manifolds than non power steering cars. These first engines also had interchangeable left and right exhaust manifolds.

The 303 Rocket did have one weak area however, a noisy valve train! Much of the problem originated in the poor oils available in the early days and was increased dramatically by not paying strict attention to oil change intervals. If it is necessary to replace valve train components some of the scarce (read expensive) oe parts can be substituted with more common (read much less expensive) small block Chevy parts.

All Olds 303 cam bearings are the same as Chevy #2 and #5 bearings. It takes three sets to make one, but its still much less expensive. Each bearing will need an oil hole drilled, but thats it. An Olds cam has a large base circle (large lobes) and they are becoming rare. A worn cam may be reground and reused with a set of small block Chevy lifters for much less than NOS Olds cam and lifters. You can still use the Olds push rods this way, they're the correct length!

Finally, proper lifter preload must be assured to keep your Rocket from ticking away. Lifter preload is when all the clearance is out of the valve train with the valve closed, the distance the pushrod seat in the lifter is below it's retainer. The correct spec is 0.030" to 0.050" for all stock applications.

Rod bearings are the same as those used in Pontiac 326 cubic inch to 455 cubic inch motors into the 1970's. Main bearings are not used by any other motors so they will be more rare. The main bearings are all the same except for the last (#5) bearing which is larger, and the thrust bearing. The bearing caps are numbered on their right side. If it is necessary to turn the crank 0.010" to 0.020", you won't weaken it.

303 Rocket Specs
Bore and Stroke 3 3/4 x 3 7/16 inch
Displacement 303.7 ci
Compression Ratio 7.25:1
Maximum Brake Horsepower 135 @ 3600rpm
Maximum Torque 263 lb ft @ 1800rpm
Oil pressure 40 psi
Tune up Specs
Spark Plugs AC 45; gap .030
Timing Between two balls on crank pulley (1949), middle of slot on pulley (others)
Idle Speed 375 RPM in drive (425 RPM w/manual trans)
Head Bolt Torque 65-70 lb-ft.
Compression pressure 120 psi @ cranking speed
Valve spring pressure 141 lbs @ 1 1/2in.
Valve seat angle 45 degrees
Point gap 0.016"
Piston Specs
Ring gap: Compression:
Sealed Power: 0.008"
Perfect Circle: 0.010"
Ring gap: Oil: same
Wristpin diameter 0.9803" - 0.9807"

Bearing Specs
Connecting rod bearings:
Journal Diameter 2.2488" - 2.2498"
Bearing Clearance 0.0009" - 0.0029"
Rod end play 0.002" - 0.011"
Rod Bolt Tension 45 - 50 ft-lbs

Main bearings:
Journal diameter #1,2,3,4 2.498" - 2.499"
#5 2.623" - 2.624"
Clearance #1,2,3,4 0.0005" - 0.003"
#5 0.002" - 0.0035"
Main bolt tension #1,2,3,4, 100 ft-lbs
#5 140 ft-lbs

[ Thanks to Ernie Johnson for this information ]


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