Editing Chevrolet big-block engine (section)

===427===
{| border="0" style="float:right;"
|-
|[[Image:1966 Chevrolet Corvette 427 engine.JPG|thumb|150px|L36 427 in a 1966 [[Chevrolet Corvette]]]]
|-
|[[Image:SC06 1967 Chevrolet Corvette 427 L89 engine.jpg|thumb|150px|L71 427 in a 1967 [[Chevrolet Corvette]]]]
|}
The highly successful and versatile {{cvt|427|cuin|L|1}} version of the Mark IV engine was introduced in 1966 as a production engine option for full-sized Chevrolets and Corvettes. The passenger vehicle 427 should not be confused with the tall deck 427 which was designed for light trucks and busses. The bore was increased to {{cvt|4+1/4|in|mm|0}}, with power ratings varying widely depending on the application. There were smooth running versions with [[hydraulic lifters]] suitable for powering the family [[station wagon]], as well as rough-idling, high-revving solid lifter models usually applied to a minimally equipped, plain-looking, two-door [[Chevrolet Biscayne|Biscayne]] [[sedan (car)|sedan]] fitted with the {{cvt|425|hp|0}} version of the 427 (RPO [[Chevrolet L72|L72]]).

Perhaps the ultimate 427 for street applications was the {{cvt|435|bhp|PS kW|0}} at 5800&nbsp;rpm and {{cvt|460|lbft|Nm|0}} at 4000&nbsp;rpm of torque [[Chevrolet_L72#L71|L71]] version available in 1967 to 1969 Corvettes, and in the Italian [[Iso Grifo]]. This engine was identical to the {{cvt|425|hp|0}} L72 427 (first introduced in 1966), but was fitted with 3×2-barrel [[Holley Performance Products|Holley]] [[carburetor]]s,<ref>{{cite web|url=https://www.carfolio.com/specifications/models/car/?car=44242|website=carfolio|title=1967 Chevrolet Corvette 427 L71, 1968 MY 19400|access-date=July 3, 2018}}</ref> known as "[[Tri-Power]]," in lieu of the L72's single 4-barrel carburetor. Both engines used the same high-lift, long-duration, high-overlap camshaft and large-port, cast-iron heads to maximize cylinder head airflow (and, hence, engine power) at elevated engine-operating speeds. Consequently, the engines offered very similar performance and resulted in a car whose performance was described by one automotive journalist as "the ultimate in sheer neck-snapping overkill". Typical 2000s-era magazine road tests of Corvettes with the engine yielded 0-{{cvt|60|mph|km/h}} in 5.6 seconds and [[Dragstrip|{{convert|1/4|mi|m|0}}]] in 13.8 second at {{cvt|104|mph}} range for both the L72 and L71.<ref>{{cite web|url=https://www.myclassicgarage.com/knowledge-base/1967-Chevrolet-Corvette|archive-url=https://web.archive.org/web/20180704063500/https://www.myclassicgarage.com/knowledge-base/1967-Chevrolet-Corvette|url-status=dead|archive-date=July 4, 2018|website=myclassicgarage|title=1967 Chevrolet Corvette|access-date=July 3, 2018}}</ref><ref>{{cite web|url=https://www.motortrend.com/news/1967-chevrolet-corvette-427-1968-porsche-911l-in-head-2-head/|website=motortrend|title=1967 Chevrolet Corvette 427 vs. 1968 Porsche 911L|date=13 August 2014|access-date=July 3, 2018}}</ref>

In 2011, ''Super Chevy Magazine'' conducted a chassis [[dynamometer]] test of a well documented, production-line, stock but well-tuned L-72 "COPO" Camaro, and recorded a peak {{cvt|287|hp|kW|0}} at the rear wheels, demonstrating the substantial difference between 1960s-era SAE "gross" horsepower ratings and horsepower at the wheels on a chassis dynamometer. Wheel horsepower (which is obtained at the drive wheels and thus takes into account drivetrain power loss of the transmission, driveshaft, and differential, as well as all accessories) does not equate to [[Horsepower#SAE net power|SAE net HP]] (which is horsepower at the flywheel, but with all essential peripherals included (such as the water pump, alternator,  and air cleaner), accessories (such as a power steering pump, if fitted), a stock exhaust system, and all required emission controls, none of which are accounted for in SAE gross, which only measures gross flywheel horsepower).<ref name="superchevy1">{{cite web |last=Hill |first=Patrick |url=http://www.superchevy.com/technical/additionaltech_perfdir/sucp_1102_chevrolet_muscle_car_dyno_wars/viewall.html |title=Chevrolet Muscle Car Dyno Wars |website=Superchevy.com |publisher=Super Chevy Magazine |date=February 1, 2011 |access-date=November 1, 2014}}</ref>

The RPO L89 was an L71 fitted with aluminum heads. While this option produced no power advantage, it did reduce engine (and hence, vehicle) weight by roughly {{convert|75|lb}}.{{cn|date=May 2024}} Although the difference in straight line performance was negligible, the weight savings resulted in superior vehicle weight distribution and improved handling and braking.

====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}}.

==== Mark IV 427 performance specifications ====
{| class="wikitable"
|-
!First<br />Year
!Last<br />Year
!Engine<br />Code
!Features
!Compression<br />ratio
!Factory<br />Gross Power<br />Rating
|-
|1966||1969|| L36 || 4-barrel || 10.25:1 || {{cvt|390|hp|kW|0}}
|-
|1966||1969|| L72 || 4-barrel + solid-lifters, more aggressive cam and high flow cylinder heads||  |11.00:1 || {{cvt|425|hp|kW|0}}{{efn|Chevrolet actually advertised this engine as {{cvt|450|hp|kW|0}} for a short period of time. There is speculation over whether this engine actually put out {{cvt|450|hp|kW|0}} gross, or if this was a marketing oversight that was later corrected.{{cn|date=May 2024}}}}
|-
|1967||1969|| L68 || L36 with 3×2-barrel carbs. ||  10.25:1 || {{cvt|400|hp|kW|0}}
|-
|1967||1969|| L71 || L72 with 3×2 barrel carbs.||  11.00:1 || {{cvt|435|hp|kW|0}}
|-
|1967||1969|| L89 || L71 + aluminum  heads; RPO L89 also applied to L78 "375 HP" 396 engine with aluminum head option. || 11.00:1 || {{cvt|435|hp|kW|0}}
|-
|1967||1969|| L88 || Racing-spec cam, high-flow aluminum heads (casting #s varied by model year) and some upgraded, competition-grade parts || 12.50:1{{efn|L88 had a 12.5:1 compression ratio with closed chamber heads except during the last half of 1969, when it had open chambered heads that yielded 12.0:1{{cn|date=May 2024}}}} || {{cvt|430|hp|kW|0}}{{efn|L88 was rated for {{cvt|430|hp|0}} at 5200&nbsp;rpm.}}
|-
|1969||1969|| ZL1 || Aluminum block with open chamber "3946074" aluminum heads (the early Corvette RPO engine featured a closed chamber head); cam even "hotter" than L88's; upgraded parts similar to L88's || 12.00:1 || {{cvt|430|hp|kW|0}}
|}
'''Applications:'''
* 1966–1969 [[Chevrolet Biscayne]]
* 1966–1969 [[Chevrolet Caprice]]
* 1966–1969 [[Chevrolet Impala]]
* 1966–1969 [[Chevrolet Corvette]]
* 1968–1969 [[Chevrolet Camaro]] (most were dealer installed, but in 1969 both the L-72 and the ZL-1 were factory options)

'''427 production codes:'''
* LS-1: produced 1969, 10.25:1 compression, Q-jet carburetor, oval port closed chamber heads, hydraulic lifters, nodular iron crankshaft, and two-bolt main caps. It produced {{cvt|335|hp|kW|0}}.<ref name="Muscle Cars Magazine p.63">{{cite journal |journal=Guide to Muscle Cars |date=February 1987 |page=63}}</ref>
* L-36: produced 1966–69, 10.25:1 compression, Holley or Q-jet carburetor, nodular iron crankshaft, hydraulic lifters, oval port closed chamber heads, and two-bolt main caps. It produced {{cvt|385|hp|kW|0}} in 1967–68 full-size cars, {{cvt|390|hp|kW|0}} in 1969 full-size cars and Corvettes (by exhaust system).<ref name="Muscle Cars Magazine p.63"/>
* L-68: produced 1967–69, 10.25:1 compression, [[Pontiac V8 engine#347|Tri-Power]], nodular iron crankshaft, hydraulic lifters, aluminum oval port closed chamber heads, and two-bolt main caps. It produced {{cvt|400|hp|kW|0}}, and was used in Corvettes.<ref name="Muscle Cars Magazine p.63"/>