Chevy Big Block series- the 427 variations
The Chaparral and McLaren M8B raced using the 1969 ZL1 Mark IV version of the 427 with impressive results. Specifications and mechanics of the L88 production model of the engine are virtually identical to the ZL1 although the block and heads are cast from aluminum rather than iron dropping the weight by 110 lbs-now with a dry weight of 575 lbs. (261 Kg). Other peripheral pieces such as the water pump and the special race tuned intake manifold is also of cast aluminum contributing to the lower weigh scale reading which is now in the same ball park as the Chevy small block cast iron power plants. The combustion chamber in the ZL1 extends into the cylinder heads, it sports a racier camshaft, no shroud on the radiator, and the idle is very ropy. This racing engine will only run on fuel with a high octane rating of 103 or greater making the race engine unsuitable for road use. The highest octane fuel commonly available at any public service station is octane 102 RON fuel (Sunco 260).
The ZL1 engine produced results that turned this power plant into a legend and subsequent dyno tests rate the engine at 376 SAE net horse power with surges at higher rpm of up to 524 gross hp. The particular engine tested optimal carburetor tuning, perfect ignition timing, open long tube racing headers, no air cleaner, and no power reducing accessories. There was another dyno test done on a different ZL1 engine this time in a COPO Camaro. This engine had been newly rebuilt and partially blueprinted but produced similar results with almost identical figures. The ZL1 427 engine was never produced in large quantities so very few units were available for testing ’69 and ’70. A well-tuned ZL1 engine in a stock car the engine not uncommonly turns in recorded times of 13.1 seconds for the quarter mile and reaching 110 mph which supports the 376 Net hp figure. Super Stock and Drag Racing Magazine recorded a professionally tuned ZL1 Camaro driver by drag race legend, Dick Harrell, doing the quarter mile in 11.62 seconds and achieve a speed of 122.15 mph. This Camaro is also equipped with S&S equal length headers, drag slicks, and has a few minor suspension revisions as well. Patrick Hale developed an accepted power/speed formula that suggests the speed trap time and the speed of 122.15 mph could have been reduced with larger racing slicks. The quarter mile results also suggest that the entire exhaust system from the manifold to the pipes was restricting the power in the production version of the L88 and the ZL1 engines. Extraordinary performance has a cost and the 427 with the ZL1 option for your 1969 Corvette was $4,718.00 which doubled the sticker price of a new Corvette in 1969. There were only 69 Camaro models with the COPO 9560 option roll off the assembly line. There were also 2 Corvette units with this factory ordered, but dealer installed, option produced in 1969.
Chevrolet turned the adaptability of the Mark IV big block components into a cash cow. They kept their parts retailers bins full of assorted high performance parts including complete replacement engines in crates; ready to drop into any appropriate model Chevrolet. Most of these items were originally meant for the Can-Am competition racing not for “over the counter” retail. They were marketed as heavy duty which is possibly an acceptable term for the equipment but actually most of these parts only increase the engines dependability at high rpm. The top power option 427 engines beginning in 1969 are equipped with a new style open “open chamber” cylinder head, up graded crankshaft, improved piston, and connecting rods which are all a result of the Can-Am racing program.
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