[ Edit | View ]
Date Posted: Monday, December 30, 10:09:21am|
General Motors designed a special 302 cu in (4.9 L) (referred to as 5.0 L) engine exclusively for the production Z/28 Camaro in order for it to meet the Sports Car Club of America SCCA Trans-Am Series road-racing rules from 1967–1969. It was the product of placing the 283 3.00 in. stroke crankshaft into a 4.00 bore 327 block. The 1967 302 used the same nodular cast-iron crank as the 283, with a forged-steel crankshaft that was also produced. This block is one of 3 displacements, 302/327/350, that underwent a crankshaft bearing diameter transformation for 1968 when the rod-journal size was increased from the 2.00 in. diameter small-journal to a 2.10 large-journal and the main-journal size was increased from 2.30 in. to 2.45. The large-journal connecting rods were heavier and used 3/8 in. diameter cap-bolts to replace the small-journal's 11/32. 1968 blocks were made in 2-bolt and 4-bolt versions with the 4-bolt center-three main caps each fastened by two additional bolts which were supported by the addition of heavier crankcase main-web bulkheads. When the journal size increased to the standard large-journal size, the crankshaft for the 302 was specially built of tufftride-hardened forged 1053-steel and fitted with a high-rpm 8.00 in. diameter harmonic balancer. It had a 3/4-length semi-circular windage tray, heat-treated, magnafluxed, and shot-peened forged 1038-steel 'pink' connecting rods, floating-pin in `69, and forged-aluminum pistons with higher scuff-resistance, better sealing single-moly rings. Its solid-lifter cam, known as the '30-30 Duntov' cam named after its .030/.030 in. hot intake/exhaust valve-lash and Zora Arkus-Duntov (the first Duntov cam was the .012/.018 1957 grind known as the '097, which referred to the last three digits of the casting number) the "father of the Corvette", was also used in the 1964-65 carbureted 327/365 and F.I. 327/375 engines. It used the '202' 2.02/1.60 valve diameter high-performance 327 double-hump `461 heads, pushrod guide plates, hardened 'blue-stripe' pushrods, edge-orifice lifters to keep more valvetrain oil in the crankcase for high-rpm lubrication, and stiffer valvesprings. In 1967, a new design high-rise cast-aluminum dual-plane intake manifold with larger smoother passage turn runners was introduced for the Z/28 that the LT-1 350 1969 Corvette and 1970 Z/28 engines were equipped with until the Q-jet carburetor returned in 1973. Unlike the Corvette, the exhaust manifolds were the more restrictive rear outlet 'log' design to clear the Camaro chassis's front cross-member. It had a chrome oil filler tube from 1967 to 1968, unique chrome valve covers that had neither the Chevrolet name or an engine displacement decal pad stamped into them, and a chrome 14.00 x 3.00 in. drop-base open-element air-cleaner assembly on a 780cfm vacuum secondary Holley 4-Bbl carburetor. A 'divorced' exhaust crossover port heated well-choke thermostat coil was used to provide cleaner and faster engine warm-up. Its single-point distributor had an ignition point cam designed to reduce point-bounce at high-rpm along with a vacuum diaphragm to advance ignition timing at idle and part-throttle for economy and emissions. Balancer and water-pump pulleys, as well as optional power-steering pulleys, were deep-groove for fan belt retention at high-rpm. In 1969, the 302 shared the finned cast-aluminum valve covers with the LT-1 350 Corvette engine. Conservatively rated at 290 hp (216 kW) (SAE gross) at 5800 rpm and 290 lb-ft at 4800, actual output with its production 11:1 compression ratio was around 376 hp (280 kW) with 1.625 in. primary x 3.00 secondary tubular headers that came in the trunk when ordered with a 1967 Z/28, and associated carburetor main jet and ignition timing tuning. In 1968, the last year for factory headers, they had 1.750 in. primaries x 3.00 secondaries. A stock 1968 Z/28 with the close-ratio transmission, optional transistorized-ignition and 4.88 gear, fitted with little more than the factory plenum cowl cold-air induction and headers, was capable of running 12.9 second/108 mph 1/4-mile times on street tires.
After the 1967 Trans-Am campaign with the 4-Bbl induction system producing more horsepower than the competing auto makers' 8-Bbl systems, for 1968 Chevrolet developed a factory 'cross-ram' aluminum intake-manifold package using two Holley 600cfm mechanical-secondary carburetors for Trans-Am racing. It was available only as off-road service parts purchased over the Chevrolet dealership parts counter. With the Chevrolet '140 1st-design off-road cam, the package increased a stock 302's hp from 360 hp to approximately 400. Chevrolet went so far as to carry the positive crankcase ventilation (PCV) system over to the cross-ram induction system to retain emissions compliance mandated for U.S.-produced cars beginning in 1967, that also provided full-throttle crankcase pressure venting to the intake air to burn its vapors. Engines prepared for competition use were capable of producing 465 hp with little more than the 8-Bbl induction, ported heads with higher pressure valvesprings, roller rocker arms, and the '754 2nd-design road-race cam. 1967/1968 models' cowl-induction system had an enclosed air-cleaner assembly ducted from its passenger side into the firewall cowl above the heater core. In 1969, factory ZL-2 cowl-induction hoods were available for both the single and dual four-barrel induction systems that were sealed to the air-cleaner base ensuring cooler, high-pressure, dense air from the center of the base of the windshield was supplied to the engine for combustion smoothness and maximum power production. Another popular service-parts-only component used on the 302 was the magnetic-pulse Delco transistor-ignition ball-bearing inductive-ignition distributor, introduced in 1967 and also used in the L88 427 Corvette, that eliminated the production breaker-point ignition allowing greater spark energy and more stable ignition-timing at high engine speeds.
The 302's bore/stroke and rod/stroke geometries made it a natural high-rpm engine and were responsible for its being among the more reliable production street engines homologated for full-competition across all the American makes winning back-to-back Trans-Am Championships at the hands of Mark Donohue in 1968 and 1969. Trans-Am rules required that all engine components have original equipment manufacturer production part numbers and be purchased through the respective factory dealerships. However, with engines built by Al Bartz, Falconer & Dunn and Traco Engineering, the pinnacle of the 302's use in professional racing was its being the primary engine that powered the outstanding but overshadowed 1968-1976 SCCA Formula 5000 Championship Series, a SCCA Formula A open-wheel class designed for lower cost. The engine was also popular in Formula 5000 racing around the world, especially in Australia and New Zealand where it proved slightly more powerful than the Repco-Holden V8. Weighing 1350 lbs., with a 525-550 hp iron block and head engine positioned near the car's polar moment for responsive turn pivoting, a Hewland 5-spd. magnesium transaxle, and 10 in. wide 13 in. front/20 in. wide 15 in. rear magnesium wheels, it produced incredibly exciting racing. They ran 0-60 mph in 2.8 seconds and over 180 mph. Reminiscing about the series, mid-70's Australian F5000 driver Bruce Allison said, “We never used first gear at the start. We started in second, and even then there was so much torque, you’d get wheelspin through third and fourth gears.” Prepared with a Lucas-McKay mechanically-timed fuel-injection individual-stack magnesium induction-system that was paired with ported production-car double-hump iron heads, a rev-kit fitted roller-lifter camshaft, roller bearing rocker arms, and a virtually stock production crankshaft, it had a lasting impact on the series' ability to conduct high car-count finishes and close competition events by the degree of mechanical success it provided to a series filled with star international Grand Prix drivers like David Hobbs, Brian Redman, Jody Scheckter and Mario Andretti.
[ Post a Reply to This Message ]