Editing Chevrolet big-block engine (section)

====ZL1====
The all-aluminum 1969 ZL1 version of the 427 engine was developed primarily for [[Can-Am]] racing,{{cn|date=May 2024}} which did not require homologation to compete,; it was very successful in cars like the [[McLaren M8A|McLaren M8B]]. The ZL1 specifications were nearly identical to the production L88 version of the 427, but featured an aluminum block in addition to aluminum cylinder heads. The first Corvette with the RPO ZL1 engine package was built in early December 1968 and featured aluminum closed chamber heads shared with the L88. Both L88 and ZL1 optioned cars continued to be built with closed chamber heads until approximately March 1969, when the open combustion chamber aluminum heads finally were in production and began being fitted to the L88 and ZL1 engines. The ZL1 engine also featured a lightweight aluminum water pump, a camshaft that was slightly "hotter" than the L88's, and a specially tuned aluminum intake manifold. Like the L88, the ZL1 required 103 [[Octane rating|octane (RON)]] (minimum) fuel (102 octane RON [Sunoco 260] represented the highest octane gasoline sold at common retail stations), used an unshrouded radiator, and had poor low-speed idle qualities – all of which made the two engines largely unsuitable for street use. 

As impressive as the ZL1 was in its day, actual engine dyno tests of a certified production line stock ZL1 revealed {{cvt|376|hp|kW|0}} SAE net with rated output swelling to {{cvt|524|hp|kW|0}} [[Horsepower#SAE gross power|SAE gross]] with the help of optimal carb and ignition tuning, open long tube racing headers, and with no power-sapping engine accessories or air cleaner in place.<ref name=CRG-COPO427>{{cite web |last1=Glowacki |first1=Bill |title=COPO 427: The Relentless Pursuit of Acceleration |url=http://www.camaros.org/copo.shtml |department=CRG Research Report |year=2014 |publisher=Camaro Research Group |access-date=November 1, 2014|display-authors=etal}}</ref>  A second engine dyno test conducted on a second production line stock (but recently rebuilt and partially blueprinted) ZL1 revealed nearly identical figures for the various "gross" conditions.<ref>{{cite magazine |title=Chevy 427 Dyno Results |url=http://members.cox.net/harddrivin1le/ZL1DYNOTEST.JPG |archive-url = https://web.archive.org/web/20111112211831/http://members.cox.net/harddrivin1le/ZL1DYNOTEST.JPG | archive-date = 2011-11-12 | pages=20–24|magazine = Musclecar Enthusiast |url-status=dead }}</ref>

Period magazine tests of the ZL1 were quite rare due to the rarity of the engine itself. ''High-Performance Cars'' tested a production line stock, but well tuned, example and recorded a 13.1 second/{{cvt|110|mph}} {{convert|1/4|mi|m|0}}, which correlates quite well with the previously referenced {{cvt|376|hp|kW|0}} SAE Net figure. ''Super Stock and Drag Racing Magazine'' recorded an 11.62 second/{{cvt|122.15|mph}} {{convert|1/4|mi|m|0}} in a professionally tuned ZL1 Camaro with open long-tube S&S equal-length headers, drag slicks, and minor suspension modifications, driven by drag racing legend Dick Harrell{{Citation needed|date=April 2025}}. Using Patrick Hale's Power/Speed formula, the {{cvt|122.15|mph}} trap speed indicated low 11-second ET (elapsed time) potential (e.g. with larger drag slicks) and suggested something on the order of {{cvt|495|hp|kW|0}}, "as installed", in that modified configuration{{Citation needed|date=April 2025}}. This large difference in power suggests that the [[Original equipment manufacturer|OEM]] exhaust manifolds and exhaust system were highly restrictive in the ZL1 application, as was also the case with the similar L88.

The then-staggering $4,718 cost of the ZL1 option doubled the price of the 1969 Corvette, resulting in just two production Corvettes (factory option at dealer) and 69 of the 1969 Camaros (non-dealer option from factory – COPO 9560) being built with the ZL1.

Chevrolet capitalized on the versatility of the 427 design by producing a wide variety of high-performance, "over-the-counter" engine components as well as ready-to-race [[Automobile engine replacement|"replacement" engines]] in shipping crates. Some of the components were developed to enhance the engine's reliability during high RPM operation, possibly justifying the use of the description "heavy duty." However, most of these items were racing parts originally designed for Can-Am competition that found their way onto dealers' shelves, and were meant to boost the engine's power output.

Beginning in 1969, the highest performance 427 models were fitted with the new open (vs. closed) chamber cylinder heads, along with design improvements in crankshafts, connecting rods, and pistons, adopted from the Can-Am development program.

Chevrolet gave all 427 engines except the ZL1 a torque rating of {{cvt|460|lbft|0}}.