Throwback Thursday-1962: the Oldsmobile Jetfire explained

The turbocharger is so ubiquitous now that even those who have no interest in cars to speak of will have at least heard of him.

That’s probably in part because these devices are fitted to all types of engines these days, from 0.9-litre three-cylinder superminis up to V12s in supercars, and in part because the word “turbo” in essence has come to mean something powerful and cool during the 1970’s.

However, this technology has not been in the mainstream for very long. In fact, while the turbocharger was invented way back in 1905 and used in American aircraft during the second World War, its first automotive application was not until 1962.

Turbos appeared in a pair of General Motors (GM) models: in the first place, the Chevrolet Corvair Monza and, after a few weeks, the Oldsmobile Jetfire. These were not the first forced induction cars, however, cars, including that of Graham’s eight-cylinder engine (1934), Cord 812 (1937) and Studebaker Golden Hawk (1957) already had used superchargers.

On the 27th of April 1967, the Coach of the JP Norbye explained how the Jetfire of the novel device worked.

“By the addition of the turbocharger to the [3.5-liter, aluminum-block] engine V8, the Oldsmobile engineers have gained a 40% increase of power in the mid-speed range,” he wrote. In fact, the turbo engine made 215bhp, offering a 0-60 mph in less than 9.0 sec. And, surprisingly, this was done “without affecting the engine’s flexibility, durability, or fuel economy”.

“These results could not have been obtained by the increase of the cylinder capacity of the engine or the installation of a larger, existing unit. Optimization of the basic V8 engine by raising the compression ratio, the installation of larger carburetors, the review of the adaptation and modification of the camshaft would lead to a higher range of power gain, but a loss of flexibility and an increase in the consumption of fuel.”

The turbocharger was supplied by Garrett AiResearch, an innovative aerospace company whose products include intercoolers, turbines, cabin pressurization systems and the beginning of the flight computers, and whose exploits later included involvement with the first turbo car to win the Indy 500, the first turbo car to win at Le Mans and the first production turbodiesel car (the US-market-only Mercedes-Benz 300SD 1978).

The idea for the use of a turbocharger had come from GM’s head of engine development engineer, Gil Burrell, who had remembered an extensive technical report on the subject that the company had committed “many years before” and decided to enthusiasm to continue with research, which led him to get in contact with Garrett.

The mechanism that resulted was described by the Coach as “extremely elaborate, with numerous safety devices”.

We said: “Those who are familiar with engine turbo diesel engines [these had already been used in locomotives and trucks] may be surprised that it was necessary to complicate the machinery of both simply because the driving sucks through a carburettor and not a pure admission of air.

“But a little thought made it clear that the blower pressure has to be limited. The high volumetric compression ration of 10.25:1 it is also necessary to inject water-alcohol mixture, and the carburetor is coupled to a measuring device, with connections to a bypass should the fluid reservoir run dry.”

That mixture, comically christened as ‘Turbo Rocket Fluid’ consisted of 50% methyl alcohol and 50% distilled water and a small amount of anti-corrosion additives. This served to prevent the detonation because the first prototypes of the engines suffered from spark knock. The alcohol serves as an anti-freeze, it is possible to use the same fluid, regardless of the weather,” and was applied between the carburetor and the compressor.

We explained the following: “The nozzle is located in a part of the passage that way a long venturi to obtain the desired pressure drop; the ratio of liquid fuel remains close to 10:1 throughout the engine’s rpm range.”

Of course, in a naturally aspirated engine, this fall is created when a cylinder falls during the intake stroke, while the turbo technology enables air to be sent to the engine to a pressure higher than the atmospheric (‘boost’ pressure).

“Under cruising or coasting conditions, with the throttle partially open, there is a high degree of vacuum in the intake manifold, so that there is a check valve in the metering system to prevent the liquid from being absorbed into the motor at low or no boost pressure. When the increase of the pressure in the manifold reaches 1psi, a diaphragm in the fluid metering valve opens a ball check valve, and the pressure in the fluid container tank forces the fluid through a jet nozzle injection.”

Oldsmobile V8 consumed the liquid at a speed of around 8000mpg, but the deposit was a mere of 4.7 liters, which means that it can be emptied in less than 250 miles. When it was empty, the performance would drop significantly (despite the fact that it was perfectly fine to drive the car), which leads to many owners who had not filled out the deposit to take the car back to the dealer and complain.

Given the complexity of the system, it was natural that some cars suffered mechanical problems, too, and all this for Oldsmobile offer to replace the complicated turbocharger mechanism conventional 4 cylinder with carburetor. This means that it is now almost impossible to find an “original” Jetfire because only 9607 examples were produced and most of the owners accepted the offer of a replacement.

The Jetfire’s turbocharger was fitted to the top of the engine, with the turbine and the compressor mounted on a single shaft”. It was smaller than the Corvair, with a compression diameter of 2.5 in (2.4). Its speed range was 6000 to 90,000 rpm in crankshaft speed-of 14,000 rpm, the turbo pressure was only 14.7 psi.

Our report, said: “the Maximum efficiency is designed to come in between 2000 and 2200rpm, but the momentum is still high to 5000rpm. The maximum power is developed at 4600rpm, as against 4800rpm for unblown versions of the V8.

“In normal driving conditions, the turbine will cruise at 40,000 rpm. For maximum acceleration, the throttle is wide open, and the turbocharger has a very fast response, speeding up to about 80,000 rpm in less than a second.”

The most amazing part of all this, the Coach of the man considered, was that “the turbo is absolutely quiet and free of vibrations, not only at a normal speed, but also when it accelerates, reaching a maximum and idling.”

While a valiant effort, neither GM turbo pioneers became trendsetters, with the first real success of turbo cars do not come until the decade of 1970, in the form of the BMW 2002 Turbo, Porsche 911 Turbo and the Saab 99 Turbo – although, sadly, sans Turbo Rocket Fluid.