In 1962 and 1963, Oldsmobile offered a short-lived turbocharged version of the compact F-85. Called F-85 Jetfire, it used a high-compression aluminum V-8 engine with a complex, troublesome fluid injection system. Chevrolet also developed a simpler turbocharger installation for the air-cooled flat-six engine of the rear-engined Corvair. The Corvair offered turbocharged engines from 1962 to 1966.
Chevrolet Turbocharges the Corvair
By that time, news of the Oldsmobile turbocharger was beginning to spread, both in the industry and within GM. In June 1961, the project unexpectedly became a race, as Chevrolet began a crash program to add a turbocharger to the Corvair.
The ostensible rationale for turbocharging the Corvair’s air-cooled “Turbo-Air” flat six was similar to the rationale for turbocharging the F-85: There were limits to how much Chevrolet could increase the displacement of the air-cooled flat-six engine — at that time 145 cu. in. (2,372 cc) — and extracting more horsepower risked hurting driveability. As it was, the RPO 649 High Performance Turbo-Air engine had rather racy valve timing and a noticeably lumpy idle.
During this period, there was a good deal of aftermarket hop-up equipment available for the Corvair, including at least three different engine-driven supercharger kits. Chevrolet engineers claimed to have considered and rejected a crankshaft-driven supercharger, saying it would have consumed too much power, taken up too much space, and coexisted too uneasily with the blower belt that drove the engine’s cooling fan. There was probably something to those arguments, but it also can’t have escaped Chevrolet that there was the possibility of a world first.
The Corvair turbo package, developed by engineers Robert E. Thoreson and James O. Brafford, bore only the broadest resemblance to its Oldsmobile rival. Chevrolet used a larger turbocharger, supplied by the Thompson Products Valve Division of Thompson Ramo Wooldridge, Inc. (later TRW, Inc.), with a 2.97-inch (75.4-mm) turbine driving a 3.00-inch (76.2-mm) centrifugal impeller, drawing through a 1.31-inch (33.33-mm) Carter Model YH side-draft carburetor and producing maximum boost of 11 psi (0.76 bar) from about 3,500 to 4,500 rpm. The turbocharger had no wastegate, boost being regulated solely by the restriction of the single-throat carburetor and dual-outlet muffler.
The turbocharged engine combined the hotter camshaft from the RPO 649 engine with the lower 8.0:1 compression ratio of the base Corvair six, and incorporated a host of modifications to enable the air-cooled engine to survive the greatly increased temperatures and pressures that accompanied turbocharging: a nitrocarburized (Tufftrided) chromium steel forged crankshaft; exhaust valves of Nimonic 80A nickel-chromium alloy with chromium-silicon steel valve stems and aluminum bronze valve guides; reinforced pistons with chrome-plated compression rings; stronger connecting rods; and an oil separator to deal with the increased blow-by. Because prolonged periods at maximum boost could increase cylinder head temperatures precipitously, Chevrolet also opted to include a cylinder head temperature gauge as standard equipment on turbocharged cars.
Perhaps the Corvair engine’s most unusual feature was in its distributor, which provided an initial spark advance of 24 degrees before top dead center (BTDC) and replaced the usual vacuum advance with a pressure-controlled retarding device that could retard the spark timing by up to 9 degrees under boost, to prevent detonation.
The Oldsmobile F-85 Jetfire and Chevrolet Corvair Monza Spyder
Oldsmobile officially announced its turbocharged engine when the 1962 models debuted in the fall of 1961, but production was delayed until spring. Chevrolet beat Oldsmobile to the punch both in offering turbocharged preview cars for the press to sample and in delivering production models in dealerships, albeit only by about two weeks. Both cars went on sale in April 1962, the world’s first turbocharged production cars.
Oldsmobile and Chevrolet took different approaches to marketing their respective turbocharged engines. Chevrolet made the turbocharger part of a new “Spyder” option package (RPO 690) for the Corvair Monza, and initially required buyers to also order various a number of other performance options. Oldsmobile initially told the automotive press the turbocharged engine would be available as an option on all F-85 models, but when it finally arrived in showrooms, it was offered only on a new top-of-the-line F-85 model, called Jetfire.
Where the Spyder package was available on Monza coupes and convertibles, the F-85 Jetfire was sold only as a two-door hardtop — the sole pillarless hardtop in the F-85 line — with a list price of $3,049, $355 more than a Cutlass coupe. The price premium wasn’t outlandish compared to contemporary aftermarket supercharger kits, which typically cost at least $300 (not including installation, if you weren’t equipped to do it yourself), but it was still a lot of money for 1962.
Aside from its hardtop roof, the F-85 Jetfire was identified by dual wind splits on the hood, brushed aluminum side trim, distinctive emblems, and dual exhaust outlets. Inside, the Jetfire was largely similar to the F-85 Cutlass, with a deluxe interior featuring bucket seats, “Morrocceen” vinyl upholstery, full carpeting, and chrome highlights. Standard equipment included a center console, on which was mounted a “Turbo-Charger” gauge whose needle swung between green “Economy” and red “Power” quadrants to indicate when the engine was operating under boost. The gauge was more a gimmick than a useful instrument, and its position and angle made it difficult to see while driving. Unlike the Spyder package, which included a new instrument panel to accommodate the head temperature gauge and a tachometer, the Jetfire made do with the standard F-85 dashboard, which remained free of distracting instrumentation other than the speedometer and fuel gauge.
Like any F-85, the Jetfire’s standard transmission was a column-shifted three-speed manual (a Warner Gear T-85 unit with unsynchronized low), although very few cars were so equipped — according to Jetfire expert Jim Noel, just 16 ’62 Jetfires and a further 45 ’63s had the manual three-speed. Sometime after launch, a floor-shifted four-speed manual transmission (the ubiquitous Warner Gear T-10 box with its “wide-ratio” gearset) became optional, listing for $199.80. However, most Jetfires had automatic transmission, the unloved three-speed Hydra-Matic, a $189.00 option.
(We’ve observed that there’s some argument about whether the Hydra-Matic used in the Jetfire and other Y-body Oldsmobiles had three or four speeds. The answer is “three,” although 1962 Oldsmobile brochures and factory literature described the Hydra-Matic as a four-stage (“4-S”) transmission, arguing that the small amount of additional torque multiplication the “Accel-A-Rotor” in the fluid coupling provided when starting from rest in first (or reverse) constituted an additional “stage.” By that standard, Chevrolet’s two-speed Powerglide, whose torque converter provided additional torque multiplication in both low and high gears, could also be considered a four-speed automatic!)
The Jetfire came standard with the same 3.36:1 axle ratio used on the Cutlass, although the taller 3.08:1 “expressway” axle used on the manually shifted F-85 was theoretically optional, and an anti-spin differential was available for an extra $43.04. Standard tires were 6.50-13, although 7.00-13 and 6.00-15 tires were optional. Suspension and brakes were standard F-85 fare, and unless you talked a dealer into installing the police car chassis parts, the only heavy-duty option available was stiffer rear springs, intended for trailer towing.
Typically for this era, Jetfire buyers paid extra for features like backup lights, two-speed windshield wipers and windshield washer, and outside mirrors. There was also the usual range of options, including power steering, power brakes, power windows, tinted windows (either all around or just the windshield), air conditioning, and radio. A fully loaded Jetfire listed for almost $4,100, about as much as a well-equipped 1962 Chevrolet Impala Super Sport with a 409 cu. in. (6,702 cc) engine.
The Turbo-Rocket Engine
Naturally, the principal attraction of the F-85 Jetfire was not the tinsel, but the “Turbo-Rocket” engine, identified by a “T” suffix in the engine serial number and immediately recognizable thanks to its distinctive side-mounted air cleaner and the turbocharger’s prominent exhaust inlet and outlet pipes.
The Turbo-Rocket engine had the same 10.25:1 compression ratio as the four-barrel Cutlass engine and used the same camshaft as its normally aspirated siblings. However, despite the single-throat carburetor, the turbocharged Jetfire engine claimed 215 gross horsepower (160.3 kW) and 300 lb-ft (406.7 N-m) of torque. This was 30 hp (22.4 kW) more than the Cutlass engine and 65 hp (48.4 kW) more than the Corvair Monza Spyder, which claimed 150 gross horsepower (111.9 kW) and 210 lb-ft (284.7 N-m) of torque, although the Corvair engine had a modest edge in specific output: 1.036 hp/cubic inch (63.24 hp/liter), versus 0.999 hp/cubic inch (60.94 hp/liter) for the Olds.
With a light foot on the accelerator, it was possible to drive the Jetfire with little or no boost. At idle, engine exhaust flow was barely enough to overcome the turbine’s inertia, and at “road load” (i.e., in steady-speed top-gear cruising), the turbocharger loafed at around 3,000 rpm at 30 mph (48 km/h), only exceeding the 10,000-rpm mark above about 50 mph (80 km/h). However, the little turbine responded swiftly to a tap on the loud pedal, accelerating by as much as 30,000 rpm in less than a second. With a more aggressive throttle foot, boost pressure began to build by as little as 1,200 engine rpm. Upon achieving maximum boost — officially 5 psi (0.34 bar), “5 to 6 psi” (0.34 to 0.41 bar) according to the Jetfire service manual — the wastegate would begin to open, holding boost at a more or less constant level until the turbine reached its maximum speed, which corresponded to about 4,000 engine rpm at wide open throttle. If the wastegate controller was disabled (intentionally or not) or the bypass valve failed to open properly, boost pressure exceeding 6.5 to 7.5 psi (0.45 to 0.52 bar) would close the auxiliary throttle valve, restricting airflow to the compressor.
Above 4,000 engine rpm, boost pressure would gradually taper off as engine speed increased, limited by carburetor venturi area. Although the Jetfire engine would rev to 5,000 rpm or more, there was little to be gained by doing so, as power fell off sharply above about 4,600 rpm. This was to some extent by design; the small carburetor’s limited high-rpm breathing made it difficult to overspeed the turbocharger. (The turbine’s normal maximum speed was 96,000 rpm, but the rotating assembly was balanced for up to 100,000 rpm, and its burst speed was 150,000 rpm, providing a greater safety margin than most crankshaft-driven superchargers of the time.)
As we noted earlier, this boost curve was designed to emphasize midrange torque, which it did. Oldsmobile’s published torque curves (which unfortunately we don’t have in reproducible form to include here) indicate that at wide open throttle, the Turbo-Rocket engine’s gross torque output was about equal to that of the normally aspirated Rockette engines just off idle and surpassed them by about 1,400 rpm, cresting in a fat swell from the arrival of maximum boost around 2,100–2,200 rpm to the 3,200 rpm gross torque peak. Even as torque began to decline at higher rpm, the Turbo-Rocket retained a significant torque advantage over both the two-barrel and four-barrel normally aspirated engines. By contrast, the Corvair Monza Spyder engine didn’t reach 1 psi (0.07 bar) boost until 2,500 rpm, and its gross torque peak was a rather lonely spire, climbing sharply to a narrow peak between 3,200 and 3,400 rpm before dropping off almost as precariously. The Corvair engine could rev higher, but the turbocharged Oldsmobile engine had more torque over virtually the entire operating range, meaning more horsepower at all speeds.
Nonetheless, the drop-off in power at higher rpm made clear that the Jetfire’s “1 horsepower per cubic inch” gross output — at 4,600 rpm — was strictly a paper rating. In the April 1963 issue of Motor Trend, editor and engineer Roger Huntington presented the results of a revealing series of tests conducted by drag racer Dick Griffin, using a four-speed 1963 F-85 Jetfire provided by Demmer Tool & Die Company in Lansing (which would later assemble the 1968 Hurst/Olds) and taking not only acceleration times, but also accelerometer readings that enabled Huntington to calculate actual horsepower at the clutch. In stock form, Huntington estimated that the Jetfire engine had an as-installed output of 155 hp (115.6 kW) at 3,800 rpm with 5.5 psi (0.38 bar) maximum boost, the latter confirmed with a calibrated manifold pressure gauge. Griffin and Huntington subsequently learned that Oldsmobile had fitted some early 1963 Jetfires with the 2.00-inch (50.8-mm) tailpipe used with the four-barrel Cutlass engine rather than the 2.25-inch (57.2-mm) exhaust pipe used on the 1962 Jetfire, only to revert to the wider pipe as a running change after realizing that the narrow ones cost too much power. Fitting the wider tailpipe to the Demmer car added what Huntington calculated was an additional 5 hp (3.7 kW).
Based on this data, we would estimate that the net output of a healthy stock Jetfire fresh out of the showroom was between 150 and 160 horsepower (112 and 119 kW) at 3,800 to 4,000 rpm. This was not as much stronger than the Corvair Monza Spyder as the engines’ respective gross ratings would suggest; a Spyder engine in good tune had at least 120 to 125 net horsepower (89.5 to 93.2 kW). However, we would estimate that the Jetfire made at least 15 net hp (11 kW) more than the normally aspirated four-barrel Cutlass engine, and substantially more torque as well.
Huntington unfortunately didn’t calculate net torque curves for the engine in Griffin’s Jetfire, but 155 hp (115.6 kW) at 3,800 rpm would require 214 lb-ft (290 N-m) of torque at that speed, which was probably at least 600 to 800 rpm beyond the turbocharged engine’s torque peak. Our very tentative guess — which we must emphasize is our surmise, not Huntington’s — is that the Turbo-Rocket engine’s net torque curve was approximately the same shape as the gross torque curve, peaking at perhaps 250 lb-ft (340 N-m) at something between 2,800 and 3,000 rpm, which was the operating regime for which the turbocharger was optimized. (As a point of interest, 250 lb-ft (340 N-m) was also the nominal input torque capacity of the light-duty Hydra-Matic transmission used on the F-85, although the units used on Jetfires had a somewhat higher torque capacity.)
Oldsmobile noted that all aluminum Rockette V-8s required a longer-than-usual break-in period (a consequence of the hard iron cylinder liners), and sure enough, Griffin found that about 3,000 miles (4,800 km) of wringing out provided a noticeable increase in engine power. He also tinkered with the boost controller by adding shims to the spring that controlled the wastegate bypass valve, a warranty-voiding modification that raised maximum boost pressure to 6.5 psi (0.45 bar) — as much as the system would permit without disabling all the various boost-limiting features — and increased net output at the flywheel to an estimated 175 hp (130.5 kW) at 4,000 rpm. That output would require 230 lb-ft (312 N-m) of torque at 4,000 rpm, which suggests a higher net torque peak (perhaps as much as 270 to 275 lb-ft (365 to 373 N-m)) and a commensurately fatter torque curve. However, even with that modification and running with open exhausts, the turbocharged engine was still 10 hp (7.4 kW) shy of its gross power rating.
Nevertheless, for 1962, these were quite decent figures for a mildly tuned street engine of this displacement, and the Turbo-Rocket engine remained smooth, quiet, and flexible, displaying almost none of the turbo lag that afflicted the peaky turbocharged Corvair engine. In most respects, the turbocharger installation made a 215 cu. in. (3.5-liter) engine perform like a normally aspirated 300 cu. in. (4.9-liter) V-8, while adding just 36 lb (16.3 kg) — 11 percent — to the weight of the engine. Also, even at its maximum speed, the AiResearch turbocharger consumed only 6 hp (4.4 kW), less than half as much as a Paxton-McCulloch supercharger producing about the same boost.
Turbo-Rocket Fluid Injection
Based on all that, the Jetfire’s Turbo-Rocket engine seemed like a winner, but inevitably, there was a catch.
Compressing air increases its temperature due to adiabatic heating and friction from the compressor. When compressed air is drawn into an engine’s intake valves, the pistons compress it again during the engine’s compression stroke, which heats the air even more. This added heat increases the risk that part of the mixture will explode rather than burning in a controlled manner when the spark plugs fire, an event known as either preignition or detonation, depending on whether it occurs during or after the completion of the compression stroke. The greater the heat, and the greater the danger of preignition or detonation, either of which can cause severe engine damage.
During the period when Oldsmobile developed the Jetfire, the conventional wisdom was that in a supercharged engine, adding boost pressure of 6 psi (0.41 bar) was equivalent to a 2-point increase in compression ratio. Given the octane ratings of contemporary premium fuels, a compression ratio of 11.0:1 was considered the practical upper limit for a normally aspirated street engine running on pump gasoline, so the practical limit for a mildly supercharged street engine was about 9.0:1. Even those limits could be dicey for an engine with too much carbon buildup, requiring adjustments to ignition timing to avoid engine knock. That was why when Studebaker-Packard first offered a McCulloch supercharger as a factory option in 1957–1958, the compression ratio of the Studebaker V-8 was reduced to a mere 7.5:1, making for weak performance at lower engine speeds despite seemingly robust gross ratings of 275 hp (206.1 kW) and 333 lb-ft (451 N-m) of torque.
Nevertheless, Oldsmobile had insisted on a 10.25:1 compression ratio for the Turbo-Rocket engine. One of the goals for the project was that the turbocharged engine’s off-boost performance should be at least as good as that of the regular-fuel two-barrel F-85 engine, and with the single-throat carburetor and the added back pressure and additional frictional and pumping losses created by the impeller, that would have been difficult to achieve without a higher compression ratio. Moreover, even under boost, a lower compression ratio would have involved greater sacrifices in fuel economy and torque than Oldsmobile engineers were prepared to accept. Oldsmobile apparently never actually built any low-compression turbocharged engines for evaluation, but it seems likely that such an engine would have been no more powerful than the four-barrel Cutlass engine, rendering the more complex turbocharger installation somewhat pointless.
The obvious problem was that with such a high compression ratio, detonation became a risk with anything more than minimal boost. At full throttle, the compressor raised the intake charge temperature by up to 140 degrees Fahrenheit (60 degrees Celsius), and retarding the ignition timing (as Chevrolet did with the Spyder engine’s boost-operated spark control) and/or enriching the mixture to prevent detonation would have significantly reduced torque and fuel economy. This was a dilemma that had arisen during the development of supercharged aircraft engines prior to World War 2, and the solution Oldsmobile adopted would have been familiar to military flight and maintenance crews of 20 years earlier: fluid injection, using what Oldsmobile dubbed “Turbo-Rocket Fluid.”
Fluid injection, more precisely known as antidetonant injection (ADI), was first tried on aircraft engines during WW1 and again in the early thirties, but the availability of higher-octane aviation fuels had delayed its widespread adoption until WW2. By 1941, however, fluid injection systems were being hastily added to many military aircraft engines as a way to extract more horsepower for takeoff and in what U.S. armed forces called “war emergency power” mode. After the war, ADI had seen some use in civilian aircraft, and there were a number of attempts to market fluid injection systems for car and truck use, the earliest of which was probably the Thompson Products Vitameter, first advertised in 1945. The GM Research Laboratories’ 1958 experimental Oldsmobile engine had also used fluid injection to control detonation.
ADI is often called “water injection,” but while pure water is effective as an internal coolant, its high freezing point makes it impractical for many ADI applications. Antidetonant fluids generally include least 30 percent ethyl or methyl alcohol, which isn’t as effective as water as a coolant, but usefully lowers the freezing point of the fluid and allows greater detonation-limited power output. During WW2, methanol was preferred over ethanol, although both were used, and it wasn’t uncommon to also add small amounts of soluble lubricants or anti-corrosion additives to help protect rubber hoses and seals from the alcohol’s corrosive effects. Despite its silly name, Oldsmobile’s Turbo-Rocket Fluid was fairly typical of wartime antidetonant fluids: a 50–50 mixture of distilled water and methyl alcohol with a small amount of corrosion inhibitor. (For comparison, the Thompson Vitameter used “Vitol,” later renamed “Vitane,” an 15-85 water-alcohol mixture supplemented with soluble oil and a few cubic centimeters of tetraethyl lead.)
AiResearch was originally supposed to develop the ADI system along with the Jetfire turbocharger, but the initial version was unsatisfactory, so the final system was designed by Rochester along with the special Model RC carburetor. Boost pressure exceeding about 1.0 psi (0.07 bar) would pressurize the antidetonant fluid reservoir and the underside of a float chamber in the fluid control valve assembly. This forced fluid into the float chamber and applied boost pressure to the diaphragm under the float, unseating two diaphragm-operated check balls and allowing intake vacuum to draw a small amount of Turbo-Rocket Fluid through the fluid outlet in the throttle bore, below the primary throttle valve. (Pedants may wish to note that this is technically carburetion rather than injection, and indeed, some sources describe the Jetfire throttle bore as a “water carburetor.”)
Under boost, the metering system added antidetonant fluid to the mixture at a rate of about one-tenth the rate of fuel flow. The fluid acted as a coolant, absorbing heat to prevent detonation. Contrary to what you might assume, diluting the air-fuel mixture in this way actually added 5 or 6 hp (3.7 to 4.4 kW), which more or less equaled the power consumed by the turbocharger’s additional back pressure. Fluid injection also slightly reduced on-boost fuel consumption.
The rate at which the Turbo-Rocket Fluid was consumed varied considerably with driving style. With the 5-quart (4.7-liter) reservoir, even an aggressive driver would likely have enough fluid for at least a tank or two of fuel. In gentler driving, the fluid supply might conceivably last up to 8,000 miles (12,800 km). (By comparison, a turbo-supercharged WW2 fighter engine could consume a 15-gallon (57-liter) supply of antidetonant fluid in just five minutes of war emergency power.) A low-fluid warning light on the otherwise useless console-mounted Turbo-Charger Gauge illuminated when the reservoir fell below about 15 percent of its capacity. There was a bracket in the engine compartment for carrying an extra bottle in case you needed to top up while out of range of an Oldsmobile dealer, as the service manual was emphatic not to use substitute fluids.
If the fluid supply was exhausted, the metering float would drop to the bottom of its chamber, opening the boost limit control valve and closing the auxiliary throttle valve. This didn’t completely block airflow to the compressor, which would have stalled the engine, but it restricted airflow enough to limit boost to no more than 1.0 psi (0.07 bar), at which level Oldsmobile claimed the engine could get by indefinitely without fluid injection. As an additional precaution against overboost, the fluid reservoir pressure cap would pop open if boost pressure exceeded 6.5 to 7.5 psi (0.45 to 0.52 bar); with the pressure cap open, the fluid metering float would drop and the auxiliary throttle valve would open to restrict airflow, just as if the system were out of fluid. (The cap could be closed and reset, but doing so required opening the hood.) If the engine was shut off, a depressure valve in the throttle body was supposed to exhaust any residual pressure in the fluid reservoir within two minutes, to prevent fluid from entering the cylinders in liquid form and causing hydrostatic lock.
This was all very elaborate, but it’s difficult not to see the Turbo-Rocket Fluid system as a serious miscalculation. Even a completely automated ADI system required a reasonably advanced level of knowledge; a driver or pilot didn’t necessarily need to understand the principles involved or the finer points of the system’s operation, but they did need to grasp at least generally what the fluid injection system was for, what would happen if it failed or the fluid supply was exhausted, that the fluid reservoir needed to be periodically checked and replenished, and which reservoir to fill. It was one thing to fit an ADI system to a military aircraft or race car, where the system would be refilled and inspected regularly and crews could be trained in how to properly use and maintain it, but this was a lot to ask of an average passenger car owner of no particular mechanical knowledge or aptitude.
Granted, cars of this era required far more regular maintenance than modern automobiles do, so Oldsmobile may have rationalized the ADI system as no worse than an engine requiring a quart or two of oil between changes, which was considered normal at the time. However, even an owner who had their car regularly serviced by the dealer might still run out of fluid at an unexpected moment, and we doubt the typical service station attendant of the time would have thought to ask, “Top up yer Turbo-Rocket Fluid?” while wiping the windshield and checking the oil.
Given the design parameters for the Jetfire, Oldsmobile would probably have been better off compromising a bit on the compression ratio and adding an air-to-air or air-to-water intercooler to reduce the temperature of the compressed mixture before it entered the intake manifold. Intercoolers were not new technology; they had been used for decades with other types of air compressors, and both Büchi and Rateau had noted that it might be desirable to use an additional radiator to cool the compressed intake charge. Intercoolers had been common on supercharged aircraft engines since the twenties, despite significant penalties in weight and aerodynamic drag, and were an essential feature of WW2 turbo-superchargers. AiResearch was certainly familiar with charge cooling, having built aftercoolers for cabin pressurization systems since the late thirties and intercoolers for aircraft engines since around 1941.
As far as we’ve been able to determine, Oldsmobile either never considered the possibility of intercooling or else dismissed it at an early conceptual stage. Packaging would probably have been a concern, as Olds engineers were very keen to minimize the size and weight of the turbocharger installation (for obvious reasons, given the dimensions of the F-85 engine bay), and they wanted to keep the impeller as close as possible to the intake manifold to reduce lag. The ADI setup scored well in those respects, but for the kind of car the Jetfire was intended to be and the kind of performance it offered, the fluid injection system was a mistake — both too much of a gimmick and not enough of one. It would become the Jetfire’s Achilles’ heel.
F-85 Jetfire Performance
Published performance figures for the F-85 Jetfire fell into two general categories: preview drives of early factory demonstration cars on the GM Proving Grounds in Milford, Michigan, which were encouraging, and independent tests conducted in the real world, which tended to be disappointing.
Preview tests consistently reported 0–60 mph (0–97 km/h) times of about 8.5 seconds, which was brisk for this era, if not in the same league as the hottest big-engine full-size cars of the time. Probably the most complete summation of these preview drives was presented in the June 1962 issue of Car Life, whose results included the following figures for a 1962 Jetfire with Hydra-Matic, the standard 3.36:1 axle and 6.50-13 tires, a curb weight of 2,860 lb (1,297 kg), and a test weight of 3,160 lb (1,433 kg):
- 0–30 mph [0–48 km/h]: 2.9 seconds
- 0–60 mph [0–97 km/h]: 8.5 seconds
- 0–100 mph [0–160 km/h]: 28.2 seconds
- Standing quarter mile, elapsed time: 16.5 seconds
- Standing quarter mile, trap speed: 80 mph [129 km/h]
Those figures made the Jetfire substantially quicker than the regular Oldsmobile F-85 Cutlass with its normally aspirated four-barrel V-8, examples of which Oldsmobile helpfully provided for comparison. The Cutlass, which had the same transmission, gearing, and tires as the Jetfire and weighed 40 lb (18.1 kg) less, needed 10.9 seconds to reach 60 mph (97 km/h) and 37.0 seconds to reach 100 mph (160 km/h).
The Car Life editors didn’t record an observed top speed for the Jetfire, but asserted that it would reach 107 mph (172 km/h) “under favorable circumstances.” Unless “favorable circumstances” included different gearing, we’re skeptical, since reaching that speed with the 3.36:1 axle would have required the engine to pull to 5,100 rpm in high. Most contemporary performance tests found the Turbo-Rocket engine ran out of breath in top gear at approximately the same point as the normally aspirated Cutlass (if not sooner, given the smaller carburetor), giving the Jetfire a similar top speed: around 103–104 mph (165–167 km/h).
Subsequent tests of the production Jetfire, farther away from the ministrations of Oldsmobile engineers, found its acceleration notably less impressive, as summarized in the following table. (Note that all metric equivalencies in brackets are our calculations, not included in the original test results.)
|Magazine||Issue||Transmission||Axle Ratio||Curb Weight||Test Weight||0–30 mph [0–48 km/h]||0–60 mph [0–97 km/h]||Quarter Mile [400 m] Elapsed Time||Quarter Mile [400 m] Trap Speed|
|Motor Trend||Sep. 1962||Hydra-Matic||3.36:1||2,856 lb [1,295 kg]||3,250 lb [1,474 kg]||3.7 seconds||10.2 seconds||18.7 seconds||80 mph [129 km/h]|
|Car Life||April 1963||4-speed||3.36:1 (see Note 1)||2,930 lb [1,329 kg]||3,290 lb [1,492 kg]||3.2 seconds||9.8 seconds||17.1 seconds||80 mph [129 km/h]|
|Motor Trend||April 1963||4-speed||3.36:1 (see Note 2)||2,880 lb [1,306 kg] (see Note 2)||3,050 lb [1,384 kg] (see Note 2)||3.5 seconds||9.1 seconds||17.0 seconds||83 mph [134 km/h]|
- Note 1: This second Car Life test car had 6.50-14 tires, a $13.45 option on 1963 Jetfires without air conditioning, which should have slightly reduced (numerically) its overall gearing compared to the standard 6.50-13 tires, although that difference wasn’t reflected in the spec sheet’s calculated data.
- Note 2: Dick Griffin tested this car with non-stock 7.00-14 tires (which also would have slightly reduced overall gearing compared to the standard 6.50-13 tires), and with only a half-tank of fuel; weights with a full tank would have been about 50 lb (22.7 kg) greater. The listed acceleration figures are for his initial test run, without additional break-in miles or the subsequent “adjustments” to the boost controller.
Both the 1962 Motor Trend and 1963 Car Life reviews complained about the disappointing acceleration and wondered if their Jetfire test cars weren’t producing their full rated power. However, it’s interesting to note that their quarter mile trap speeds (the speed at which the car crossed the quarter mile line) were identical to the earlier preview drive, which, given the cars’ similar weight and gearing, suggests that their actual horsepower was probably about the same. (Griffin’s car was 3 mph (5 km/h) faster through the quarter, but its test weight was about 200 lb (90 kg) lighter, which likely accounted for most of the difference.)
Why were the preview cars quicker? They clearly had the benefit of more thorough break-in — the subsequent road test cars all had significantly less mileage — but it’s also possible the Oldsmobile press preview cars had had some of the same kind of boost controller fiddling Dick Griffin’s car later received, which would have provided a noticeable increase in torque (and thus stronger acceleration) through most of the rev range. Any such adjustment might have still technically been within allowable specification, and in any case wouldn’t have been detectable without installing a proper manifold pressure gauge, so it would rate at least a B+ in the realm of creative road test preparation, a minor art form in this period.
Even with the preview cars, testers complained that performance was hampered by the lethargy of the optional Hydra-Matic transmission, which was fitted to more than 80 percent of F-85 Jetfire production. The units fitted to Jetfires were supposed to be recalibrated to suit the turbocharged engine, with different shift points, higher line pressure, and a different band servo, but the results don’t appear to have been any better than the standard Hydra-Matic, whose slow shifts and sluggish response were a frequent complaint among F-85 owners as well as contemporary road testers, who preferred the four-speed manual. In practice, the latter didn’t make a dramatic difference in overall performance, although it did provide better quarter mile elapsed times than did the automatic.
With either the four-speed or Hydra-Matic, the F-85 Jetfire was quicker than the Corvair Monza Spyder at most legal speeds and much easier to drive. Despite a 300 lb (135 kg) weight advantage and shorter gearing, the Spyder engine’s turbo lag and narrow power band put it at a significant disadvantage at lower speeds, although a well-tuned, competently driven stock Spyder might conceivably edge out the bigger, more powerful Jetfire through the quarter mile. The turbocharged Corvair also had a higher top speed than the Jetfire, thanks to superior aerodynamics and a higher rev limit. A 1963 Motor Trend road test of a Monza Spyder convertible found it needed 4.5 seconds to reach 30 mph (48 km/h) and 11.1 seconds to hit 60 mph (97 km/h), but went on to an observed maximum speed of 110 mph (177 km/h) at 5,500 rpm.
Disappointingly, while contemporary Jetfire reviews explained how the fluid injection system was designed to restrict boost if the Turbo-Rocket Fluid tank was empty, we didn’t find any published tests describing the engine’s real-world performance in that state, which seems like it would have been easy enough to arrange. Oldsmobile claimed that performance with the auxiliary throttle valve closed was similar to that of the F-85’s two-barrel regular-fuel V-8, which was adequate but uninspired. (A standard F-85 with Hydra-Matic needed 14.0 to 14.5 seconds to reach 60 mph (97 km/h), with the standing quarter mile coming up in the mid-19-second range with quarter mile trap speeds between 68 and 70 mph (110 and 113 km/h).)
As far as we could determine, only Motor Trend bothered to measure the Jetfire’s fuel economy, reporting an average of 14.1 mpg (16.7 L/100 km), compared to the 15.8 mpg (14.9 L/100 km) they recorded for an automatic Cutlass a year later. A well-broken-in four-speed car, driven with fewer attempts to test the limits of available boost, would probably do a bit better, but the F-85 Jetfire was not outstandingly thrifty, and premium fuel was required, to say nothing of the need for Turbo-Rocket Fluid. We assume that running the engine without Turbo-Rocket Fluid would return somewhat poorer fuel economy than an F-85 with the normally aspirated two-barrel engine, due to the added back pressure of the turbocharger and the additional pumping losses imposed by the auxiliary throttle valve.
Because the Jetfire package did not include any upgrades to the steering, suspension, brakes, or tires, the F-85 Jetfire handled and stopped no better than did any other F-85 or Cutlass. Unlike the swing-axle Pontiac Tempest, the F-85 was unlikely to make any unexpected moves, and it benefited from having less weight on the nose than some of its contemporaries did. However, steering was slow and vague, and the spring and damping rates were chosen for a plush ride on smooth pavement, so there just wasn’t enough body control for anything other than fairly sedate cruising. Brakes were another dynamic sore point: Y-body Oldsmobiles made do with a mere 127 square inches (819 square centimeters) of effective brake lining area, and pronounced nose dive in hard stops made it difficult for the rear brakes to do their share, resulting in long stopping distances and heavy fade even by contemporary standards.
In these respects, the F-85 Jetfire wasn’t any worse than any other F-85 or Cutlass (or for that matter the Buick Special or Skylark), but it wasn’t any better either, disappointing for an ostensibly sporty car. This was a common problem for American Supercars, whose acceleration frequently outstripped their cornering and stopping ability. Oldsmobile would do better with the subsequent A-body 4-4-2, which had a much better-sorted chassis, though not necessarily better brakes.
11 CommentsAdd a Comment
Pleased to see this. Impressive, as usual.
There may have been an antidetonant for other applications at the time. If so, I’m betting that the manufacturer never explicitly marketed it to Jetfire owners.
I’m not sure if Thompson was still selling Vitane by this point, but it wouldn’t have been ideal for the Turbo-Rocket V-8 anyway. At any rate, Oldsmobile literature most emphatically discouraged using substitute fluids, which was understandable, since using a different fluid risked either diminishing the effectiveness of the system or risking it freezing in cold weather.
There were a number of technical papers published toward the end of WW2 summing up wartime experience and best practices with regard to fluid injection, which I suspect the engineers at Oldsmobile (or perhaps Rochester, who designed the final injection system) read and took to heart, as they followed those recommendations quite assiduously.
I remember reading that the F85 – in its earliest development stage – was to have a transverse 60 degree V6, and an automatic transaxle that used the hardware from the Roto-5 automatic but with three chains to connect engine to gearbox to wheels. It was killed early in the development stage – due to cost, of course – but we did get something useful from that project. The 60 degree V6 developed by Olds engineers sat on the shelf until the late 1970s when a narrow V6 was needed for the upcoming X car. The Olds design was handed to Chevrolet to get them started and then they finalized the engine for production. But if you look carefully at the 2.8/3.1 V6 from the early 80s, you can see details in the block – notably timing chain area – that look a lot like the small block Olds V8. In fact, it looks a lot more like an Olds motor than a Chevy.
What hit the showrooms in late 1960 was fairly conventional, but looking at the MSRP that would be in the high $20k in 2023 dollars, there wasn’t much engineering magic they could include without pricing the car out of the market or losing a lot of money on every one they sell.
It’s true that Oldsmobile did experiments with FWD for a car the size of the F-85, but the timetable makes it unlikely it would have been for 1961. The first FWD test mule wasn’t built until early 1960, when the initial production F-85 was very close to pre-production. At that point, the FWD project was at a rather nascent stage (the test mule weighed about 600 lb more than a RWD F-85, the chain drive was still quite crude, they were still evaluating whether they needed two CV joints per side, and I think it was using pieces of an older four-speed Hydra-Matic), so even if the division had been enthusiastic and corporate management had signed off on it for production, I think it would likely have been for a second-generation F-85. There simply wouldn’t have been time to get it into producible shape for 1961.
(There is some confusion on the timeline, stemming in part from the fact that both Oldsmobile Advanced Design Group and the corporate Engineering Staff were working on the project concurrently in different ways. (Oldsmobile asked Engineering Staff to develop a gear-drive transfer unit, which involved a Buick Dual Path Turbine Drive two-speed automatic.) However, Andy Watt, who was head of Advanced, said unequivocally that until early 1960, Oldsmobile FWD prototype development was still only at the stationary test rig stage.)
I have seen Oldsmobile engineers attribute the Chevrolet 2.8-liter V-6 to the abortive Oldsmobile FWD project. However, I’m very skeptical of the idea that it “sat on the shelf” until the seventies or that an almost 20-year-old design for an unproduced Oldsmobile experimental engine would be “handed” to Chevrolet. Weird things happen sometimes, so I suppose it’s not outside the realm of possibility, but it seems more like a piece of internal folklore born of old divisional rivalries. I’ve never found any substantive details about the V-6 used in the FWD mules (neither the SAE paper nor the GM Engineering Journal articles about Oldsmobile FWD development even mention its displacement), and since that engine never got close to production, it’s not a claim that seems particularly verifiable. Also, the “small block” Oldsmobile V-8 — by which I assume you mean the 330/350/307 rather than the aluminum Rockette engine — didn’t yet exist as such in 1960 (the bulk of its initial development was in 1962 and early 1963), although it’s possible that the experimental V-6 previewed certain details later used on that engine. To the extent that the 2.8-liter V-6 looks “like an Olds motor,” it seems more plausible that the source of inspiration was the smaller Oldsmobile V-8, which WAS a production engine, and a very familiar one by the time the FWD X-body cars were in development.
(At a glance, the most obvious resemblance between the 2.8-liter V-6 and the Oldsmobile V-8 is the way the block forms a kind of integral shroud for the timing chain. Oldsmobile said they did that because they wanted to be able to use a flat timing chain cover, while Chevrolet’s explanation was that it allowed them to avoid using a steel backing plate for the cam drive.)
Great article as usual! Thanks.
Not only did turbocharged Corvairs have a cylinder head temperature gauge, there was also an under-dash buzzer that alarmed if the head temp get too high. I’ve read that Chevrolet engineers were worried about sustained high loads like pulling a trailer or climbing a long, steep mountain pass and wanted an audible alarm to get the driver’s attention to back off the throttle.
Some of the period testers noted that while there was a cylinder head temperature gauge, the gauge didn’t provide any specific indication of how high was too high, so supplementing it with a buzzer was prudent. That notwithstanding, adding the new instruments rather than simply an amber “HEAD TEMP” light in the existing panel was a worthwhile move, and suggested that despite the comparative simplicity of the Spyder package, Chevrolet engineers had a clearer idea of its potential market and what those buyers might want.
I think it had all three: a gauge, an idiot light, and a buzzer. I’ve never driven a Corvair turbo but I’ve had several Corvairs and all had a combination head temp/oil pressure idiot light. As far as I know the turbo kept that and added the gauge and buzzer.
Your extensive follow up on later turbocharged cars was fascinating, especially the point about Porsche not producing a 911 turbo until 1975, 13 years after the Corvair turbo. It seems as if the Corvair wasn’t so much a poor man’s Porsche, rather, the 911 turbo should rightly be considered a rich man’s Spyder.
Porsche’s 1978 SAE paper on their turbocharging development makes clear that they were aware of the Spyder and Jetfire (as one would expect), but were not terribly familiar with them, asserting, for example, that they were made only in 1964 and 1965.
At any rate, what’s distinct about how Porsche approached turbocharging was that it was an offshoot of their racing efforts; their first turbocharged 917 was for the 1972–73 Can-Am series, and the development of the 930 and 935 followed that. Competition has shaped a lot of automotive turbocharging development, and so it’s notable that it WASN’T a factor in the creation of the Jetfire or Spyder. Oldsmobile didn’t develop the Jetfire as an homologation special, and while Chevrolet created the Spyder in large part to try to bolster the credibility of the Corvair Monza as a sporty car, it was neither developed for or as a street version of any racing project.
Marvelous. As usual.
I am–again–impressed with both your research and your ability to write about it.