1956 285HP Engine - Pontiac GTO Forum
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Location: Gastonia, NC - Born & raised in Connecticut - 31 years
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1956 285HP Engine

My first car was a 1956 Pontiac 4-Dr Ht when I was 16. It was 19 years old then. So I have a soft spot for the '56's. I also have a factory 2 x 4 intake for the '56 which I picked up when I owned my '56. The waterneck is not original nor is the linkage.

The blue & white car was at the Pontiac Nationals. It is a documented and restored original 285HP car with 3-speed on the column. It was for sale as well.

Here is the Pontiac that started it all, the 1956 Pontiac with the optional 285HP dual 4-barrel engine. This was Pontiac's entry for Nascar racing and was to be readied for the Daytona Speed Week in February 1956. Junior Johnson is known to have wrecked 5 of them. The engine was rated at 285HP @ 5100 RPM's and 330 Ft lbs of torque @ 3600 RPM's. These engines were later available as production engines and as a dealer installed option. It is believed that 200 - 205 manifolds were produced making the number of cars manufactured near 200 with about 12 cars known to exist. A/C was not available with this engine and it had poor streetability as it was a race engine.

In June 1956, 73 year old race car driver Ab Jenkins drove a 285HP Pontiac over a 10 mile circular course set-up at the Bonneville Salt Flats. It was an attempt to break the 24 hour American unlimited and C-Class record. The car averaged 126.02 for the first 100 miles and averaged 118.375 MPH over the 24-hour period to break the existing record which Jenkins had set 24 years earlier in a special Duesenberg racing car. Jenkins drove the car for 18 hours while his son drove it for 6 hours. The distance covered was 2,841 miles.

Motor Trend test drove the car and covered its performance in the July 1956 edition. Gas mileage in stop & go traffic was 11.4 MPG. 0-60 MPH took 11.9 seconds and the 1/4 mile stood at 18.2 seconds @ 75.5 MPH. However, the author pointed out that the car only had 66 miles on it and performance was not going to be the best until it had been broken in with more miles on the car. The car exhibited an unpleasantness around town driving, but when taken to the open road, the "beast" settled down and showed a real potential for high speed acceleration.

The block code was HY. The short block was the same as any 316 cubic inch engine. Pontiac offered the 7.9 compression ratio in the economy engine by using a dished piston and 8.9 in the standard engine using a flat top piston. Both engines used head casting #522010 . The standard head casting #522010 could be milled .072 per a Pontiac Service Bulletin to achieve a 10-to-1 compression. It appears this was done at first and the completed heads were stamped with the letter code "A" to identify them. A later and separate head casting #522845 , is said to have a smaller combustion chamber to acheive the 10-to-1 compression ratio. However, The valves were the same diameter size as the standard head except 3/32" longer to compensate for the head milling which would have lowered the valve stems and changed valve train geometry if the standard valves had been used. Heavier dual springs were used on the valves and no oil shields were used on the intake valves. 97 octane was required on this engine.

The intake was produced with 2 casting numbers. Cast in January-February is the "Developmental" intake identified as D-32960. The later March-September production casting number is #523554 . The intake uses a special waterneck similar to the 1957 tripower.

Two identical Rochester carbs with chokes and idle circuits were fitted to the cast iron intake. They were not progressive, but were hooked in unison. A special fuel pump with larger valves was used to ensure adequate fuel flow at high speeds. A special 2/4 Bbl air cleaner was used which looks similar to the Cadillac 2x4 air cleaner. The small "pods" that housed the oil bath air cleaners are offset and could swivel out away from the engine rather than removing them for ease of making engine adjustments - something the Caddy or Chevrolet air cleaner didn't do.

The ignition included a Delco dual point distributor with no vacuum advance. A heavy duty coil and resistor block were added. Special mounting brackets were used for the coil and generator with the generator getting a larger 3.5" diameter pulley (vs stock 2.875" dia) to keep the RPM's down at high speeds. Engine timing was 10 degrees BTC @ 650 RPM's while the mechanical distributor advance provided an additional 20 crank degrees @ 4000 RPM's for a total of 30 degrees.

The camshaft was part #522869 . Intake duration was 289 degrees while exhaust duration was 298 degrees. Lift was .409" intake/.413" exhaust. Lobe Separation Angle was 111.2. This was a radical cam in a 316 cubic inch engine. Solid lifters were first employed in the engine and later a special hydraulic lifter was used with a higher bleed down rate to allow for higher RPM's without lifter "pump-up." The specail lifters were visibly different and stamped with an "A".

Other special engine parts rounded out the package like special valve covers, draft tube, gas lines, and valley cover, just to mention a few. Pontiac also offered a compliment of heavy-duty suspension parts aimed at racing. The 285HP engine was also used by drag racers........and at least 1 moonshine runner.
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