The
ChevroletChevrolet , also known as Chevy , is a brand of vehicle produced by General Motors Company . Founded by Louis Chevrolet and ousted GM founder William C. Durant on November 3, 1911, General Motors acquired Chevrolet in 1918...
Corvair engine was a
flat-6A flat-6 or horizontally opposed-6 is a flat engine with six cylinders arranged horizontally in two banks of three cylinders on each side of a central crankcase...
(or boxer engine) piston engine used exclusively in the 1960s
Chevrolet Corvair-First generation :The 1960 Corvair 500 and 700 series four-door sedans were conceived as economy cars offering few amenities in order to keep the price competitive, with the 500 selling for under $2,000...
automobile. It was a highly unusual engine for General Motors: It was air-cooled, used a
flat designA flat engine is an internal combustion engine with multiple pistons that move in a horizontal plane. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is sometimes known as the boxer, or horizontally opposed engine. The concept was patented in 1896...
, with aluminum heads (incorporating integral intake manifolds) and
crankcaseIn an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...
, with individual iron cylinder barrels. The heads were modeled after the standard Chevrolet
overhead valveAn overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block , and uses pushrods or rods to actuate rocker arms above the cylinder...
design, with large valves operated by rocker arms, actuated by pushrods run off a 9 lobe camshaft (due to the unique engine layout, exhaust lobes operated valves on *both* sides of the engine), running directly in the crankcase bore without an inserted bearing, operating hydraulic valve lifters, as used on most Chevrolet OHV engines.
The flat horizontally opposed ("
flat engineA flat engine is an internal combustion engine with multiple pistons that move in a horizontal plane. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is sometimes known as the boxer, or horizontally opposed engine. The concept was patented in 1896...
") air-cooled engine design, previously used by
VolkswagenVolkswagen is a German automobile manufacturer and is the original and biggest-selling marque of the Volkswagen Group, which now also owns the Audi, Bentley, Bugatti, Lamborghini, SEAT, and Škoda marques and the truck manufacturer Scania.Volkswagen means "people's car" in German, where it is...
and
PorschePorsche Automobil Holding SE, usually shortened to Porsche SE a Societas Europaea or European Public Company, is a German based holding company with investments in the automotive industry....
as well as
LycomingLycoming Engines is a U.S. aircraft engine company, known primarily for its general aviation engines. For most of its history Lycoming has been part of the AVCO group as AVCO Lycoming. In 1987 AVCO was purchased by Textron to become Textron Lycoming...
aircraft engines, offered many advantages. Unlike inline or V designs, the horizontally opposed design made the engine inherently reasonably well balanced, so that counterweights on the
crankshaftThe crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
were generally not necessary, reducing the weight greatly. Eliminating a water-cooling system further reduced the weight, and the use of aluminum for the heads and crankcase capitalized on this weight reduction; so that with the use of aluminum for the transaxle case, the entire engine/transaxle assembly weighed under 500 pounds (225 kilograms). In addition, the elimination of water-cooling eliminated several points of maintenance and possible failure, reducing them all to a single point; the fan belt. As with the Volkswagen and Porsche designs, the low weight and compact but wide packaging made the engine ideal for mounting in the rear of the car, eliminating the weight and space of a conventional driveshaft.
Two years after its 1960 debut, the Corvair engine gained another unusual attribute: it was the second production engine ever to be equipped from the factory with a
turbochargerA turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
, released shortly after the
OldsmobileOldsmobile was a brand of American automobile produced for most of its existence by General Motors. It was founded by Ransom E. Olds in 1897. In its 107-year history, it produced 35.2 million cars, including at least 14 million built at its Lansing, Michigan factory...
Jetfire V8.
Aircraft hobbyists and small volume builders, perhaps seeing the Corvair engine's similarity to Lycoming aircraft engines, very quickly began a cottage industry of modifying Corvair engines for aircraft use, which continues to this day. The Corvair engine also became a favorite for installation into modified Volkswagens and Porsches, as well as dune buggies and homemade sports and race cars.
140
The initial Corvair engine displaced 140 CID and produced 80 hp (60 kW). The high performance optional "Super TurboAir" version, introduced mid 1960 with a special camshaft and revised carburetors and valve springs produced 95 hp (70 kW).
145
In 1961, the engine received its first increases in size via a larger bore. The engine was now 145 CID and the base engine was said to produce the same 80 hp (60 kW). The new high performance engine was rated at 98 hp (73 kW). In 1962 the high performance engine was rated at 102 hp (76 kW). The high compression 102 hp heads were added to the Monza models equipped with Powerglide when the standard engine was ordered, giving an 84 hp engine rating. 1962 engines returned to automatic chokes after a one year only manual choke on 1961 models.
The ultimate performance was found in the Spyder model, which became available with a turbocharged engine rated at 150 hp (112 kW). The turbocharger was mounted on the right side of the firewall behind the rear seat, fed by both exhaust manifolds; a single side-draft carburetor mounted on the left side of the firewall fed directly into the turbocharger's intake, with a chromed pipe leading from the turbocharger's outlet to what would otherwise be the carburetor mounting pads on the intake manifolds, which were integral parts of the heads. The turbocharged heads received some valve upgrades to improve durability. Exhaust valves on turbocharged engines were made from a non-ferrous material used in jet engine turbine buckets, called "
Nimonic 80-ANimonic is a registered trademark of Special Metals Corporation that refers to a family of nickel-based superalloys. Nimonic alloys typically consist of more than 50% nickel and 20% chromium with additives such as titanium and aluminium. The main use is in gas turbine components and extremely high...
". All other Corvair engines had slight upgrades in valve and
valve seatThe valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed...
materials as well for 1962.
164
The engine's stroke was increased from 2.6" to 2.94", resulting in a displacement of 164 CID for 1964. Power output was boosted to 95 hp (70 kW) for the base model and 110 hp (80 kW) in the high performance normally aspirated engine, while the Turbocharged engine remained rated at 150 hp for this year. This increase in stroke was the maximum the engine could tolerate, to the point that the bottoms of the cylinder barrels had to be notched to clear the big end of the connecting rods.
For the 1965 model year, all engines had the head gasket area between the cylinder and the head widened, with a new design folded "Z" section stainless steel head gasket virtually eliminating any risk of head gasket failure. A 140 hp (104 kW) version with four single barrel
carburetorA carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
s, and a progressive linkage was introduced in 1965 as option L63 'Special High Performance Engine' and was standard equipment on the Corsa model. The carburetors consisted of a single barrel primary and a single barrel secondary on each head, connected by a progressive linkage; in addition, the heads featured a 9.25:1 compression ratio, and the cars received dual exhaust systems. Engines supplied with the automatic transmission after spring 1965 were modified with a camshaft from the 95 hp base engine, and a special crankshaft gear that retarded its timing 4 degrees- the former to increase torque and smooth the idle with the Powerglide transmission, the latter to restore some of the peak horsepower lost at higher engine speeds by the economy contoured camshaft with short timing.
1966 engines were basically carryover from the 1965 models, however Corvairs sold in California (except Turbocharged models) now featured the General Motors Air Injection Reactor System (AIR), an emissions control system consisting of an engine driven air pump that drew filtered air from the air cleaner, and injected a metered amount into the exhaust manifolds via tubing to promote complete oxidation and combustion of exhaust gasses to lower emissions. Specially calibrated carburetors and slight changes to the ignition timing and advance curves were part of the package. The AIR system had an unfortunate effect of substantially raising exhaust gas, valve and head temperatures, particularly under heavy loads and this was a drawback on the Corvair where engine cooling could not be easily improved to cope with the higher temperatures. Nonetheless, performance and drivability were not noticeably affected in most circumstances. In 1968, all Corvair (and other GM) engines got the AIR system for every market. The combined heat load imposed by the AIR system, along with air conditioning, made air conditioning unavailable as an option after 1967, and on all earlier Corvairs with the AIR system.
The 140 hp engine was officially discontinued for '67, but became optional in 1967 as COPO 9551-B, not a regular production option. Chevrolet sold 279 of these engines in the 1967 model year, 232 with manual transmissions, and 47 with Powerglide transmissions. Only six were sold with the four carburetor engine and the AIR injection system required by California emissions standards. These figures include 14 Yenko Stingers and 3 Dana Chevrolet variants of the Stinger. Due to demand, the 140 hp engine returned as an RPO for the 1968 model year, and was available until the end of the Corvair's run in spring 1969.
Both the 140 hp engines and the Turbocharged engines had many special quality features not shared with lesser Corvairs- Moly insert top rings, stellite tips and faces on the valves, a Tufftrided (cold gas hardened) crankshaft, and Delco Moraine '400' aluminum engine bearings- the quality of the 140 hp Corvair engine for materials is directly comparable to the Rolls Royce V8 of that era, item for item. It was a fabulous bargain for the $79 premium it commanded over the basic 95 hp engine. Performance of the 140 hp engine was better than you might expect, with a 5200 rpm peak horsepower output, it offered road performance in a Corvair comparable to contemporary Cadillac models of the day.
The turbocharged engine now developed 180 hp (134 kW). Contemporary reviews describe a similarity in power between the turbocharged and four-carburetor engines throughout the low and mid rpm range, with the turbocharged engine being superior only when it was possible to sustain boost continuously. The turbocharged engine's long suit was highway acceleration, flooring the accelerator at turnpike speeds produced ferocious acceleration in the upper speed ranges as the turbocharger began to boost, reaching manifold pressures approaching 15 PSI. No wastegate was used on the Corvair turbocharged engine; boost was controlled by careful balancing of exhaust restriction, mostly via the muffler, and intake restrictions from the smallish Carter YH carburetor used. Pre-ignition and knock under boost was controlled using a novel 'pressure retard' device, essentially a modified vacuum advance device, on the specially curved distributor, as boost pressures built, ignition advance was progressively reduced to preclude detonation.
Problems
The Corvair engine design was so unusual that good dealer service and maintenance was spotty. Mechanics, unused to the aluminum head and crankcase, would frequently overtighten threaded fasteners and spark plugs, stripping the threads out of the aluminum, requiring extensive repair.
Due to the greater
thermal expansionThermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
of aluminum, hydraulic valve lifters were used to maintain correct lash as the engine heated and the cylinders expanded. These were relatively trouble free and did not require periodic adjustment. Tuning issues related to the dual (or quadruple) carbs in non-turbocharged Corvairs sometimes led to erroneous diagnosis of valve issues in Corvairs - in fact, the Corvair had top quality valve materials in all models and valve jobs were almost never required. The valve train in most engines usually functioned perfectly for the life of the car. However, 140 hp engines did have a high percentage of dropped valve seats.
Early engines were subject to occasional failures of the head gasket, between the heads and the cylinder barrels; this was addressed in later models by increasing the width of the sealing area and redesigning the gasket material and cross section, eliminating any issues.
The large cooling fan located on top of the engine required the fan belt to bend from the vertical plane of the crankshaft to the horizontal plane of the fan, causing additional stress. Chevrolet engineers designed a unique fan belt, which many owners and dealers replaced with an inappropriate design. The correct fan belt, properly installed to proper tension, worked well, while other belts even of proper size installed loose or tight would break frequently, giving the engine fan and belt design an undeserved bad reputation. Since failure of the cooling fan on an air-cooled engine leads to immediate overheating much more quickly than in a water-cooled engine (within 15 seconds at the high RPM when the belts were likely to fail), mechanically inclined owners would routinely carry a spare belt and the -inch box end wrench needed to change the belt, in addition to adding a large and eye catching warning light in parallel with the normally sized factory generator/alternator warning light (the "GEN/FAN" light), and belt guides were added to reduce the tendency to throw a belt. Aftermarket manufacturers made available differently sized pulleys which reduced the fan speed to 1.3 or 1.2 times engine speed, rather than the stock 1.5; this reduced the tendency to throw or break a fan belt for engines which spent most of their time at higher RPM.
The pushrods were located below the cylinders, each in a separate metal tube between the crankcase and the head; these tubes also served to return oil from the head to the crankcase, and were fitted with
neopreneNeoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range...
O-ringAn O-ring, also known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a disc-shaped cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.The O-ring...
s at each end. After a short time, the neoprene exposed to the intense heat of the head lost resilience and developed a tendency to leak oil which became characteristic of Corvairs; unfortunately, since engine cooling air was diverted to the interior heater (except on early Corvairs equipped with the gasoline-fired heater), this caused an unpleasant odor in the passenger compartment. Improved elastomer "Viton" O-rings with much greater durability became available from aftermarket suppliers.
To address fuel slosh and cut-out issues in very hard cornering, some owners acquired an aftermarket kit to rotate the carburetors through ninety degrees and attach the now colinear throttle shafts of the two carburetors on each side together. However, this also eliminated the progressive feature of the stock carburetor linkage, so that performance could not be optimized both at low to midrange rpm and at high rpm.
Other owners replaced the four single-barrel carburetors with a single four-barrel carburetor, centrally mounted on a manifold with four long arms that attached to the original carburetor mounting pads on the heads. While this caused the carburetor and manifold to be slow to warm up to
operating temperatureAn operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
and therefore caused problems with flooding and cold temperature operation, it eliminated linkage problems, simplified tuning the carburetor, and provided access to the large variety of four-barrel carburetors available on the market. This modification was especially ill-suited to models with the Powerglide automatic transmission.
A factor which would have, in itself, led to the demise of the air-cooled engine design was the rapid and relatively large temperature variation of the air-cooled engine with variations in load and rpm; this would have made meeting the upcoming emissions requirements of the 1970s difficult. Engine temperatures on lower performance Corvairs with the AIR system were comparable to the Turbocharged models in some situations - head temperatures under full throttle could exceed 600 °F (315.6 °C).
Corvair engines swapped into Volkswagens
Initially, the cooling fans were designed with a twist to the vanes, so that they were only efficient when rotating in the correct direction. Early on, however, the vanes on the fan became vertical and radial, so that the fan functioned identically in either rotation. Whatever the reason for this change, one effect was that the engine could easily be configured to run in the direction opposite from stock. This proved useful for those who swapped the engine into
Volkswagen BeetleThe Volkswagen Type 1, widely known as the Volkswagen Beetle or Volkswagen Bug, is an economy car produced by the German auto maker Volkswagen from 1938 until 2003...
s and
dune buggiesA dune buggy is a recreational vehicle with large wheels, and wide tires, designed for use on sand dunes or beaches. The design is usually a modified vehicle and engine mounted on an open chassis. The modifications usually attempt to increase the power-to-weight ratio by either lightening the...
, since the Corvair engine's normal direction of rotation was opposite to that of the Volkswagen (and most other automobiles). Otherwise, the ring gear of the Volkswagen differential had to be flipped over by 180 degrees to allow the transmission's forward and reverse directions to be correct.
This swap was fairly common at the time, with the Corvair engine serving to give a power boost to Volkswagen Beetles, dune buggies, and Karmann Ghias. Excessively vigorous use of first gear would break the
transaxleIn the automotive field, a transaxle is a major mechanical component that combines the functionality of the transmission, the differential, and associated components of the driven axle into one integrated assembly....
(the prudent driver would avoid first gear altogether), and the engine cover of the Karmann Ghia would not close completely with a Corvair engine in place, but otherwise the swap was relatively problem free, as such things go.
A
conversion kit was also made that would allow the complete Corvair powertrain to be installed in the
Volkswagen Type 2The Volkswagen Type 2, officially known as the Transporter or Kombi informally as Bus or Camper , was a panel van introduced in 1950 by German automaker Volkswagen as its second car model – following and initially deriving from Volkswagen's first model, the Type 1 , it was given the factory...
. The original Volkswagen axles and constant-velocity joints were bolted to the transaxle using adapter plates. Both manual and automatic transmissions could be used. A converted Type 2 could be distinguished by the distinctive Corvair engine cooling outlets below the rear bumper, but it would otherwise appear to be stock.
Trivia and arcana
At the time of the Corvair's introduction the dealer mechanics had no training in air-cooled engines, or the thermal problems of aluminum engines (as the engines warmed up and cooled down the cast iron cylinder barrels expanded and contracted at a different rate than the aluminum crankcase and heads). Add that situation to the early Corvair engines having problems with head gaskets. The result was that the first-year Corvairs gained a reputation of head gasket problems. More than one Corvair dealership hired a local independent Porsche mechanic to come in and train their mechanics in the differences of air-cooled engines, with an emphasis on head gaskets, and the problem(s) went away.
Many Corvair engine fans acquired a second life after the demise of their engines, mounted bottom side out on the outside of the wheels of
CorvetteA corvette is a small, maneuverable, lightly armed warship, originally smaller than a frigate and larger than a coastal patrol craft or fast attack craft , although many recent designs resemble frigates in size and role...
s involved in road-racing, in order to pull air through the
brakeA brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
s and keep them cool. Lightweight and cheap, they were perfectly sized.
The single carburetor on each head of the two-carburetor engine was not mounted symmetrically in the center of the intake manifold, where it might be intuitively placed, but offset from the center, between the middle and end cylinders. Although sometimes erroneously cited as an engineering error, this was in fact an example of clever attention to detail; had the carburetor been placed in the center of the manifold, the center cylinder would have received a significantly greater air/fuel charge than either end cylinder. Instead, the carburetor was situated so that the firing order required the air flow to reverse itself when filling either of the nearer cylinders, whereas the airflow to the far cylinder was merely an extension of the airflow to the center cylinder, which was just prior in the firing order. This allowed for a more balanced filling of the three cylinders, and smoother operation.
High-performance parts manufacturer
EdelbrockEdelbrock, LLC is a specialty performance automotive and motorcycle aftermarket parts manufacturer based in Torrance, California. The company has five locations, including four in Torrance: its headquarters, a distribution center and museum, the Russell division , and the exhaust plant...
made available a set of larger-bore aluminum cylinder barrels (with cast-iron liners to withstand wear); when combined with their aluminum pushrods, the rate of thermal expansion of all parts of the valve train became compatible, so that solid valve lifters could be used, rather than the hydraulic lifters required by the stock cast iron cylinders. This in turn allowed the engine to run to higher RPM; in conjunction with the increased torque resulting from the increase in cylinder bore, this resulted in a substantially more powerful engine.
In addition, "stroker" crankshafts with longer stroke were quickly made available for the original engine. When Chevrolet increased the stroke of the stock engine, however, there was no longer room to increase it any further.
Immediately after the car became available with the original two carburetor engine, a number of manufacturers began to sell conversion kits for attachment of four carburetors, with either two stock carburetors, two of the ubiquitous
Stromberg-People:*Lyndon Stromberg, American sculptor and designer*Karl Stromberg, the villain in the James Bond film The Spy Who Loved Me*Joseph R. Stromberg, historian with the Ludwig von Mises Institute*Glenn Strömberg, Swedish soccer player...
97 carburetors, or a
RochesterRochester Products Division was a division of General Motors that manufactured carburetors, and related components including emissions control devices and cruise control systems in Rochester, New York...
two barrel carburetor for each bank of cylinders. The means of attachment varied from simple two into one adapters, to machining off the entire top surface of the intake manifold (cast as part of the head), enlarging the internal passages of the manifold, and attaching a new upper surface incorporating the appropriate mounting pads for the new carburetors. Similarly, aftermarket manufacturers provided several means of supercharging the original engine, including belt driven centrifugal, axial flow, or rotary vane type compressors. Chevrolet, seeing the marketing opportunity available in these aftermarket options, of course went on to offer its own four carburetor and turbocharged versions.
Another common modification was to exchange the four carburetors on the 140 hp engine for a single, center-mounted large Holley unit ("IECO Modification"). Metal intake pipes were used to route intake air to each of the four openings over the intake mainfold area, and the center carb was mounted at the crux of this "X" pipe setup. However, most Corvair experts today are of the opinion that the stock multi-carburetor setup is superior to the IECO modification in most ways, including driveability and performance.
Engine Serial Number Codes
The following codes (last two digits of engine serial number) identify the year, size, power, and transmission of the engine
YC 6 cyl. with M/T ......................................1962-64
YH 6 cyl. with M/T.......................................1962
YL 6 cyl. with M/T. A/C................................1962-64
YM 6 cyl. with A/C. HPE...............................1962-63
YM 6 cyl. with T/C. 4 sp. Tr.........................1964
YN 6 cyl. with M/T. HPE ..............................1962-64
YR 6 cyl. with T/C. 4 sp. fr ..........................1962
Z 6 cyl. with A/T .........................................1963-64
ZB 6 cyl. with A/T .......................................1962
ZD 6 cyl. with A/T. A/C ...............................1962-64
ZF 6 cyl. with A/T. HPE ...............................1962-64
ZG 6 cyl. with A/T, A/C, HPE........................1962-64
ZH 6 cyl. with A/T .......................................1962-64
ZJ 6 cyl. with A/T,A/C .................................1962
Y 6 cyl. with M/T HPE ..................................1962-63
RL 6-164 with T/C ......................................1966
RM 6-164 with M/T, SHPE............................1965-67
RN 6-164 with SHPE, P/G.............................1965-67
RQ 6-164 with SHPE, A.I.R............................1966-67
RR 6-164 with A/C ......................................1966
RS 6-164 with M/T, A.I.R..............................1965-68
RS 6-164 with A.I.R .....................................1966
RU 6-164 with M/T, HPE, A.I.R.....................1965-68
RV 6-164 with P/G, A.I.R..............................1965-68
RW 6-164 with HPE, A.I.R., P/G ....................1966-68
RX 6-164 with P/G, HPE, A.I.R .....................1965-67
RY 6-164 with A/C, SHPE ............................1966-67
RZ 6-164 with SHPE, A/C ............................1966-67
RA 6-164 with M/T and A/T........................1965-67
RB 6-164 ....................................................1965-66
RD 6-164 with HPE .....................................1965-67
RE 6-164 with A/C ......................................1965-68
RF 6-164 with HPE, A/C...............................1965-68
RG 6-164 with P/G ......................................1965-67
RH 6-164 with P/G, HPE ..............................1965-67
RJ 6-164 with P/G, A/C.................................1965-68
RK 6-164 with P/G, HPE, A/C .......................1965-68
QO 6-164 with P/G, A.I.R., A/C ...................1967
QP 6-164 with HPE, P/G, A.I.R, A/C..............1967
QQ 6-164 with SPHE,A.I.R.,A/C......................1967
QR 6-164 with SPHE, A.I.R., A/C, P/G............1967
QS 6-164 with HPE, A.I.R., A/C .....................1967
A/C: Air conditioned
A.I.R.: Air Injection Reactor
A/T:Automatic transmission
HPE: High performance engine
P/G: Powerglide
SHPE: Special Hi Perf. Engine
T/C: Turbocharged