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250 CU. IN. OVERHEAD CAM 6 ENGINE
Firebird, Firebird Sprint, Tempest, Tempest Custom, Le Mans, Tempest Safari
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Pontiac's famous European sports type engine with its celebrated overhead cam drive has been redesigned for 1968. Now boasting a new standard displacement of 250 cubic inches, the engine provides more torque in all driving ranges, has excellent idle characteristics and performs exceptionally well at all speeds.
An all-new 1-BBL Mono-jet carburetor, designed to significantly reduce exhaust emission and specially calibrated to substantially improve fuel flow for added driving economy, is standard on this engine with manual transmission. With this carburetor, the
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rated brake horsepower is 175 at 4800 rpm, and engine torque is 240 pound-feet at 2600 rpm.
The 4-BBL Quadra-jet carburetor is standard with this engine on Firebird Sprint, and on Tempest, Tempest Custom (except Station Wagon) and Le Mans when the "Sprint" option is ordered. When equipped with this carburetor, the rated brake horsepower increases to 215 at 5200 rpm, while engine torque increases to 255 pound-feet at 3800 rpm.
(Refer to page A-8 for Firebird Sprint features and page E-2 for "Sprint" option features.)
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Cylinder Head and Block.
The chromium iron cylinder head is cast with integral valve guides. The wedge-shaped combustion chambers are deep, and fully contour-machined, as in Pontiac V-8s. This feature promotes smooth, efficient burning of the air-fuel mixture while maintaining a relatively high compression ratio and makes the engine less sensitive to octane ratings of regular fuels. The engine block is unusually rigid, and features short crank-throw span, ideal journal overlap, short forged connection rods and deep skirt design.
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Special Cam Drive -
An outstanding feature of the OHC 6 engine is the belt-driven cam. This belt has a tension member of fiberglass with both sides surrounded by specially compounded chloroprene rubber. The meshing sides has a woven nylon fabric surface which is impregnated with the rubber. Fully oil-resistant, the belt connects the crankshaft, camshaft and accessory drive sprockets. This application permits the belt to drive the distributor, fuel pump and oil pump as one external drive assembly. Clearly defined timing marks make ignition timing extremely simple.
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Camshaft.
The camshaft for this engine is made of a special heat-treated metal alloy known as "hardenable iron," which has exceptional wear characteristics. Bearing surfaces on the camshaft are extra wide for low-contact pressures to contribute to longer engine life. The "Sprint" engine camshaft lobes, of hollow flank design, help improve performance throughout the entire speed range without the need for roller followers. This special design provides excellent idling characteristics without sacrificing the high-performance built into the engine.
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Rocker Arm and Valve Train.
Special heat-treated metal alloy rocker arm have excellent wear characteristics. And the automatic zero valve-lash adjustment is another important feature of this engine. This means that the lash adjuster is designed to permit the rocker arm and valve to operate virtually as one unit, without loss of compression, and with minimum noise, roughness and wear. The lash adjuster is hydraulically actuated, receiving its fluid from the engine lubrication system. The adjuster maintains proper relationship of rocker arm to camshaft lobe so that proper valve action is assured at all times.
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M-4
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