Dual throttle bodies, flow sensors, and computer controlled injectors – the stuff of the last 20 years delivered in 1958.

The Surprising Technology of the 1958 Chrysler 300D

Continued –

The system had issues, but all could have been fixed with more development. Frankly it is a sin that the system was installed and dumped so fast – and that Chrysler and AMC, who also was going to employ it, didn’t make any attempt to refine it. If they had, perhaps the Muscle Car and high-performance era would not have died. There are many reasons why it died still-born, and we’ll discuss how it worked and why it failed below, but four factors have to be recognized to understand why it never went any further.

• • The carburetor was cheap to make, and the industry built around that type of fuel delivery was huge. Turning those manufacturers away from their bread and butter – and the huge contracts they had with the auto manufacturers would have been like trying to get the Titanic to pivot away from the iceberg.
  • Computer science was so new and so foreign to the engineering departments at Chrysler, AMC, and others that in-house redevelopment was impossible. Relying on Bendix to fix the issues was not only threatening, but considered untrustworthy.
  • There was no such thing as emissions science or control in 1958. People knew about smog, but the root cause was still in question.
  • And if you wanted more performance? Just bold on a few more carburetors and add a radical camshaft, and there you go . . .

The Bendix “Electrojector”

Look familiar? It should – it’s the basis of all the computer-controlled fuel delivery we use today.

The story is one of a significant engineering breakthrough, but perhaps a little before its time. In fact, this system, developed by Bendix, called the “Electrojector” system, is the basis of what we see in all cars today – including the 2005-2023 Hemi. Bendix Corporation provided many electronic systems to the aircraft industry – and in that was early in on onboard interactive engine management computer systems. By 1955 they were well versed in what to do and how to do it.

Almost all of the processes that our current systems do to manage fuel flow and mixture control were developed in the 1958 original Electrojector system. We’ll talk about it in about it more detail, but know that a year or two later, the system was licensed to Bosch, who developed it and used it to handle emissions and performance in the late 70s. That system became the grandfather of today’s computer-controlled fuel management induction systems.

Let’s talk about the system how it ended up in a Chrysler 300D, and how it impacted the performance of those famous high-performance cars. First, let’s tackle the components that Bendix pioneered: the computer, the injectors, and the fuel pump.

The Computer. Understand that the computer management of anything in 1957, when it was developed, was almost science fiction. Frankly, computers doing even the simplest computations were as big as a two-car garage, and none of them could do interpretive reaction to input. They merely to a per-selected program and processed the data fed into it – usually with “punch cards”.

The computer was smaller than a loaf of bread – tiny for its time, but it handled all the decisions except spark plug firing.

A computer that could gather information such as throttle opening air flow, and temperature and then compute what fuel a metering device should deliver would have been the size of your house! The “Electrojector” computer was the size of a small loaf of bread! The formulas for what to interpret and what to do were pre-programmed and stored in the device! Looking at your phone, tablet or desktop computer – or even seeing the “E PROM” that manages this type of operation today seems ho-hum – but in 1957?

The Injectors. The 1957 injector is, for all intents and purposes, the same as we use now! Signaling for the computer told the injector how much fuel to dispense and timing of the injector pulse was regulated by a combination of mechanical signals from the distributor and the computer. They even considered a second computer to manage this timing process, but they felt that the mechanical timing was sufficient.  In actuality, the mechanical actuation was a good idea because it didn’t require a lot of wiring and was a device attached to an ordinary distributor – simple and foolproof.

The Fuel Pump. For the first time and in-tank electric fuel pump was used, just like we do today! It provided 20-35 lbs. of pressure.

The Manifold Pressure Sensor. One of the keys to the system was a device that could sense the drop in manifold pressure as the car began to accelerate. This sensor is the backdrop to what we call a “speed density” system. The relationship of this sensor to the injector is how the system managed fuel flow demands.

The manifold Pressure sensor did the job that our current MAF sensors do

There a quite a few more pieces to the process, and if you want to read the engineers’ full discussion of exactly how the system works and what components are involved, you can read the entire SAE engineering paper HERE.

We know now how much more efficient this type of system is over a carburetor, which has the fuel measuring and delivery engineering of a toilet bowl (really). Without this type of system, the horsepower and emissions of today’s cars would be unobtainable.

Conclusion. So how did it work out from an operational and performance point of view? Tom Hoover, the father of the 1954-72 Hemi, was an engineer at Chrysler when the first units were installed in a 1957 Chrysler 300C. Starting, regardless of the weather conditions, was instantaneous, and the need for warm up was almost non-existent. It was totally ubiquitous to the driver, with only the instant response to throttle pressure far better than a carbureted car. Fuel mileage increased as well, but in 1958 someone driving a Chrysler 300 hardly cared about that.

Performance. It was documented that acceleration was a minimum of 10% better. In order to increase performance by that much, at least 15% more horsepower was required. Using the factory horsepower figure of 380 for the 1958 Chrysler 300D, it would have meant that the fuel injected engine likely made about 435 advertised HP. Tom Hoover also told me that the Fuel Injected car accelerated “like Jack the Bear”, confirming that increase. A 300D with carburetors ran 16.1 in a documented test.  A 10% increase in acceleration would result in a quarter mile time of less than 15 seconds, which would have been incredible for a US passenger car in 1958.

What Happened.  If it was so great, why didn’t it stay in production? Like many innovative ideas quickly pressed into service, there are usually “teething problems”. First and foremost, was the system’s reliability. Three things impacted that: service personnel technical knowledge, damaging engine heat, and using analog (radio) signaling to the injectors.

As you likely know, heat will damage any computer system, and Chrysler erred by placing the computer under the hood of the car. Worse, this was not a printed circuit computer but a wires and capacitor unit that could easily deteriorate under heat, vibration, and time. Computer failure was common. Second, the unit had to be serviced by technicians who had never seen a computer and did not understand anything about such a thing. Third, the system’s radio signaling could easily be interfered with by AM radio stations and police band transmissions, causing the system to shut down (safely, at least, but there was no limp home.

Owners generally did not take full advantage of the power potential of the engine. And the hot and cold starting of carburetor systems, while not perfect, was well developed by this time. Most could not see the value of the system costing about $5000 in current money. Of course, the failures were a big negative.

After a few months, the cars with the system were recalled and replaced with the dual 4-barrel carburetor induction system. Chrysler did not want to deal with the issues and the publicity. Some 4-5 cars did not have the system replaced, and some do exist today, whether they run or not would be the question. Some retained the system and did not return it to Chrysler, but did use the replacement system with the dual 4-barrel setup for regular use and kept the system for “show”.