26-11-08, 03:08 PM
(Questo messaggio è stato modificato l'ultima volta il: 26-11-08, 03:08 PM da flatpaolo.)
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The highly successful and versatile 427 cubic inch (7.0 L) version of the Mark IV engine was introduced in 1966 as a production engine option for full sized Chevrolets and Corvettes. The bore was increased to 4.25 inches (108 mm), 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 that resembled racing powerplants.
Not every version of the 427 was available in every car, and ordering the highest performance versions often required that other options be added to or deleted from the car (for example, power steering wasn't available with the high performance models). This relationship between engine configuration and vehicle options often resulted in what was jokingly referred to as a "racing taxicab," the description usually applied to a minimally equipped, plain looking, two door Biscayne sedan fitted with the 425 horsepower (317 kW) version of the 427? (RPO L72), resulting in a vehicle whose performance was the polar opposite of a taxi. This lightweight, big-block Biscayne was also commonly referred to as "Bisquick."
Perhaps the ultimate 427 for street applications was the 435 horsepower (324 kW) L71 version available in 1967 to 1969 Corvettes, and in the Italian Iso Grifo. This engine was identical to the 425 hp (317 kW) L72 427 (first introduced in 1966) but was fitted with three two barrel carburetors in lieu of the L72's single 4 barrel. Both engines utilized the same high lift, long duration, high overlap camshaft and large port, cast iron heads in order to maximum cylinder head flow (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 magazine road tests of the day yielded sub-6 second zero to 60 miles per hour times and quarter miles in the mid 13 second/106 MPH range for both the L72 and L71.
RPO L89 was an L71 fitted with aluminum heads (often dealer installed). While this option produced no power advantage, it did reduce engine (and hence, vehicle) weight by roughly 75 pounds (34 kg). This resulted in superior vehicle weight distribution for improved handling, although any difference in straight line performance was essentially negligible.
The most legendary version of the 427 was undoubtedly the 1969 ZL1 engine. It was developed primarily for Can-Am racing, where it was very successful in cars like the Chaparrel 2F and McLaren M8B. The ZL1 had specifications nearly identical to the production L88 version of the 427, but featured an all-aluminum cylinder block in addition to aluminum cylinder heads, which dropped total engine weight into small block Chevy territory (approx. 575 lb/261 kg dressed). The engine was also fitted with the new open combustion chamber cylinder heads, a light weight 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 RON (minimum) fuel, which made both engines largely unsuitable for street use in an era where 102 octane RON (Sunoco 260) represented the highest octane gasoline sold at common retail stations. Impressive as the ZL1 was in its day and despite the "larger than life legends" surrounding it, actual engine dyno tests of a certified production line stock ZL1 revealed 376 SAE net HP, with output swelling to 524 Gross HP 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. ZL1 DYNO TEST - COPO CAMARO WEBSITE 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. 2nd ZL1 DYNO TEST Magazine tests of the ZL1 were quite rare due to the rarity of the engine itself. "High Performance Cars" tested a production line stock version and recorded a 13.1 second/110 MPH quarter mile, which correlates quite well with the previously referenced 376 Net HP figure. "Super Stock and Drag Racing Magazine" recorded an 11.62 second/122.15 MPH quarter mile in a ZL1 Camaro that was professionally tuned and driven by drag racing legend Dick Harrell, although that car was equipped with open long tube S&S equal length headers, drag slicks and minor suspension modifications. The 122.15 MPH trap speed indicated very low 11 second ET potential (e.g. with larger drag slicks) and suggested something on the order of 495 "as installed" HP in that modified configuration. This large difference in power suggests that the OEM exhaust manifolds and exhaust system were very restrictive in the ZL1 application, as was also the case with the similar L88.
The race-prepped ZL1s that were utilized in Can-Am racing were capable of developing something on the order of 600 "as raced" HP as the result of complete engine blueprinting, fuel injection, more aggressive cam-shaft grinds, custom fabricated, power optimizing long tube racing headers, dry sump lubrication and various other power and durability enhancing changes. It is this figure that is often erroneously cited as the "actual" output of production line stock ZL1 passenger car engines (e.g. 1969 COPO 9560 Camaro).
The 4718 dollar cost of the ZL1 option doubled the price of the 1969 Corvette, but resulted in a car with exceptional performance for its day. Just two production Corvettes (factory option at dealer) and 69 Camaros (non-dealer option from factory - COPO 9560) were 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 (marketed as "heavy duty" or "extra capacity" components to mask their intended racing application), as well as ready-to-race "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 on to dealers' shelves, and were meant to boost the engine's already impressive power output. As a result of this activity, the 427 quickly became dominant in drag racing.
Beginning in 1969, the highest performance 427 models were fitted with the new open (vs. closed) chamber cylinder head, s which along with design improvements in crankshafts, connecting rods and pistons adopted from the Can-Am development program, resulted in an engine with substantially increased performance and reliability. This development culminated in a specialty version of the engine called the ZLX, which was essentially a ZL1 engine built with the L88 engine's sturdy, four bolt main bearing iron block (it has been suggested that "ZLX" was a code name for ZL1 crossover). The ZLX, available as a short block assembly or complete "replacement" engine in the crate from a few dealers, was a resounding success and became a best-seller by after market racing components standards?the closest thing to an all-out competition engine ever offered to the general public.
Chevrolet gave all 427 engines except the ZL1 a torque rating of 460 ft?lbf (624 N?m).
First
Year Last
Year Engine
Code Features Compression
ratio Factory
Gross Power
Rating
1966 1969 L36 4-barrel 10.25:1 390 hp (291 kW)
1966 1966 L72 4-barrel + solid-lifters, more aggressive cam and high flow cylinder heads 11.00:1 425 hp (317 kW)[1]
1967 1969 L68 L36 with 3x2-barrel carbs. 10.25:1 400 hp (298 kW)
1967 1969 L71 L72 with 3X2 barrel carbs. 11.00:1 435 hp (324 kW)
1967 1969 L89 L71 + aluminum heads; RPO L89 also applied to L78 "375 HP" 396 engine with aluminum head option. 11.00:1 435 hp (324 kW)
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[2] 430 hp (321 kW)[3]
1969 1969 ZL1 Aluminum block with open chamber "3946074" aluminum heads; cam even "hotter" than L88's; upgraded parts similar to L88's 12.00:1 430 hp (321 kW)
1970 1977(?) ZLX L88-ZL1 hybrid; iron block with aluminum heads 12.25:1 430(?) hp (321 kW)
Notes:
^ Chevrolet actually advertised this engine as 450 hp (336 kW) for a short period of time. There is speculation over whether this engine actually put out 450 Gross HP, or if this was a marketing oversight that was later corrected.
^ 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
^ L88 was rated for 430 hp (320 kW) at 5200 rpm. With stock exhaust manifolds and operation in the 6,800 rpm range, it was generally accepted that the engine was capable of producing in excess of 500 Gross HP with free-flowing (open) long tube headers.
The highly successful and versatile 427 cubic inch (7.0 L) version of the Mark IV engine was introduced in 1966 as a production engine option for full sized Chevrolets and Corvettes. The bore was increased to 4.25 inches (108 mm), 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 that resembled racing powerplants.
Not every version of the 427 was available in every car, and ordering the highest performance versions often required that other options be added to or deleted from the car (for example, power steering wasn't available with the high performance models). This relationship between engine configuration and vehicle options often resulted in what was jokingly referred to as a "racing taxicab," the description usually applied to a minimally equipped, plain looking, two door Biscayne sedan fitted with the 425 horsepower (317 kW) version of the 427? (RPO L72), resulting in a vehicle whose performance was the polar opposite of a taxi. This lightweight, big-block Biscayne was also commonly referred to as "Bisquick."
Perhaps the ultimate 427 for street applications was the 435 horsepower (324 kW) L71 version available in 1967 to 1969 Corvettes, and in the Italian Iso Grifo. This engine was identical to the 425 hp (317 kW) L72 427 (first introduced in 1966) but was fitted with three two barrel carburetors in lieu of the L72's single 4 barrel. Both engines utilized the same high lift, long duration, high overlap camshaft and large port, cast iron heads in order to maximum cylinder head flow (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 magazine road tests of the day yielded sub-6 second zero to 60 miles per hour times and quarter miles in the mid 13 second/106 MPH range for both the L72 and L71.
RPO L89 was an L71 fitted with aluminum heads (often dealer installed). While this option produced no power advantage, it did reduce engine (and hence, vehicle) weight by roughly 75 pounds (34 kg). This resulted in superior vehicle weight distribution for improved handling, although any difference in straight line performance was essentially negligible.
The most legendary version of the 427 was undoubtedly the 1969 ZL1 engine. It was developed primarily for Can-Am racing, where it was very successful in cars like the Chaparrel 2F and McLaren M8B. The ZL1 had specifications nearly identical to the production L88 version of the 427, but featured an all-aluminum cylinder block in addition to aluminum cylinder heads, which dropped total engine weight into small block Chevy territory (approx. 575 lb/261 kg dressed). The engine was also fitted with the new open combustion chamber cylinder heads, a light weight 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 RON (minimum) fuel, which made both engines largely unsuitable for street use in an era where 102 octane RON (Sunoco 260) represented the highest octane gasoline sold at common retail stations. Impressive as the ZL1 was in its day and despite the "larger than life legends" surrounding it, actual engine dyno tests of a certified production line stock ZL1 revealed 376 SAE net HP, with output swelling to 524 Gross HP 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. ZL1 DYNO TEST - COPO CAMARO WEBSITE 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. 2nd ZL1 DYNO TEST Magazine tests of the ZL1 were quite rare due to the rarity of the engine itself. "High Performance Cars" tested a production line stock version and recorded a 13.1 second/110 MPH quarter mile, which correlates quite well with the previously referenced 376 Net HP figure. "Super Stock and Drag Racing Magazine" recorded an 11.62 second/122.15 MPH quarter mile in a ZL1 Camaro that was professionally tuned and driven by drag racing legend Dick Harrell, although that car was equipped with open long tube S&S equal length headers, drag slicks and minor suspension modifications. The 122.15 MPH trap speed indicated very low 11 second ET potential (e.g. with larger drag slicks) and suggested something on the order of 495 "as installed" HP in that modified configuration. This large difference in power suggests that the OEM exhaust manifolds and exhaust system were very restrictive in the ZL1 application, as was also the case with the similar L88.
The race-prepped ZL1s that were utilized in Can-Am racing were capable of developing something on the order of 600 "as raced" HP as the result of complete engine blueprinting, fuel injection, more aggressive cam-shaft grinds, custom fabricated, power optimizing long tube racing headers, dry sump lubrication and various other power and durability enhancing changes. It is this figure that is often erroneously cited as the "actual" output of production line stock ZL1 passenger car engines (e.g. 1969 COPO 9560 Camaro).
The 4718 dollar cost of the ZL1 option doubled the price of the 1969 Corvette, but resulted in a car with exceptional performance for its day. Just two production Corvettes (factory option at dealer) and 69 Camaros (non-dealer option from factory - COPO 9560) were 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 (marketed as "heavy duty" or "extra capacity" components to mask their intended racing application), as well as ready-to-race "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 on to dealers' shelves, and were meant to boost the engine's already impressive power output. As a result of this activity, the 427 quickly became dominant in drag racing.
Beginning in 1969, the highest performance 427 models were fitted with the new open (vs. closed) chamber cylinder head, s which along with design improvements in crankshafts, connecting rods and pistons adopted from the Can-Am development program, resulted in an engine with substantially increased performance and reliability. This development culminated in a specialty version of the engine called the ZLX, which was essentially a ZL1 engine built with the L88 engine's sturdy, four bolt main bearing iron block (it has been suggested that "ZLX" was a code name for ZL1 crossover). The ZLX, available as a short block assembly or complete "replacement" engine in the crate from a few dealers, was a resounding success and became a best-seller by after market racing components standards?the closest thing to an all-out competition engine ever offered to the general public.
Chevrolet gave all 427 engines except the ZL1 a torque rating of 460 ft?lbf (624 N?m).
First
Year Last
Year Engine
Code Features Compression
ratio Factory
Gross Power
Rating
1966 1969 L36 4-barrel 10.25:1 390 hp (291 kW)
1966 1966 L72 4-barrel + solid-lifters, more aggressive cam and high flow cylinder heads 11.00:1 425 hp (317 kW)[1]
1967 1969 L68 L36 with 3x2-barrel carbs. 10.25:1 400 hp (298 kW)
1967 1969 L71 L72 with 3X2 barrel carbs. 11.00:1 435 hp (324 kW)
1967 1969 L89 L71 + aluminum heads; RPO L89 also applied to L78 "375 HP" 396 engine with aluminum head option. 11.00:1 435 hp (324 kW)
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[2] 430 hp (321 kW)[3]
1969 1969 ZL1 Aluminum block with open chamber "3946074" aluminum heads; cam even "hotter" than L88's; upgraded parts similar to L88's 12.00:1 430 hp (321 kW)
1970 1977(?) ZLX L88-ZL1 hybrid; iron block with aluminum heads 12.25:1 430(?) hp (321 kW)
Notes:
^ Chevrolet actually advertised this engine as 450 hp (336 kW) for a short period of time. There is speculation over whether this engine actually put out 450 Gross HP, or if this was a marketing oversight that was later corrected.
^ 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
^ L88 was rated for 430 hp (320 kW) at 5200 rpm. With stock exhaust manifolds and operation in the 6,800 rpm range, it was generally accepted that the engine was capable of producing in excess of 500 Gross HP with free-flowing (open) long tube headers.
1971 Ford Mustang convertible 429 CJ-R
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1970 AMC AMX 390
1968 Ford Country Squire 390
1988 Chevrolet C10 stepside 292L6
1991 Jeep Wrangler Renegade 4.0HO
2007 Shelby GT-H convertible
