cazalea
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Kraftstoffeinspritzsystem aka Fuel Injection
We had a little discussion recently about the SPICA fuel injection system in the Alfa Montreal coveted by Nicolas, and it motivated me to create a short post. I will try to explain how these systems work (or not) and why they are better than carburetors (or not) and how they evolved...
First concept: Two ways to get the fuel into the engine (pardon me for using a drug culture analogy):
Carburetors are like snorting -- fuel is drawn in along with a stream of air
Fuel injectors are like shooting up -- fuel is pushed in via pressure through a small nozzle
Second concept: Engine venturi vacuum
When a piston is drawn down in the one of the cylinders, outside air wants to rush in as it is being pushed by atmospheric pressure to fill the space the piston formerly occupied. The activity of this rushing air could be called negative pressure but we commonly say vacuum. An Italian named Venturi discovered if you put a restriction / valve / choke in the air's path, it can modify the "strength" of a vacuum. When you move your foot on the throttle in a gasoline engine, it is moving a valve in the intake air stream, increasing or decreasing the mass and flow of incoming air, and the vacuum can be used to pull in fuel at the same time.
Carburetors allow an engine to draw in fuel from a reservoir (known as the float bowl) and suck it into the engine to be burned. Here's a diagram of the type of carburetor used on Jaguar, MG, Volvo, etc. You see the float chamber on the right, a pipe with fuel going to the intake air stream, a floating needle to adjust the amount of fuel being pulled in, and a throttle valve. Plus some other stuff.
Third Concept: Diesel and Gas Engines are fundamentally different
Diesel engines produce no vacuum because they are not choked! They have no throttle valve like a gasoline engine. Therefore, you can't find carburetors on a diesel engine -- diesels are always fuel injected and run only when fuel is pushed into their combustion chambers. When the fuel stops, the engine stops (most of the time). To develop a diesel engine, we had to find a way to push / inject fuel. This is much more expensive solution than the free vacuum in a gasoline engine and its simple carburetor, but there are other compensations to make it worth the money and complication.
Fourth Concept: Diesel MUST be fuel injected; Gas engines MAY be fuel injected
Because fuel injection systems push precise amounts of fuel under high pressure (because otherwise it would be pushed back out by combustion!) they are more expensive than carburetors. A necessity on diesels and a luxury on gas engines, the first production fuel injection system is credited to Mercedes-Benz in the 1950's 300SL. A very expensive car (then as now), it provided M-B sufficient revenue to adequately develop a complex MECHANICAL fuel injection pump system derived from their diesel system.
As you can see, the pump sits next to/on the engine, is driven by a shaft, has external fuel lines feeding an injector for each cylinder that goes right into the side of the combustion chamber, lots of fittings, etc. Precision and Expensive - as the Germans prefer.
At the same time (mid-Fifties) manufacturers all over the world were trying to get efficient and economical fuel injection systems into production. Here's an image of the first Chrysler semi-ELECTRONIC fuel injection system -- a couple dozen cars were sold but due to disastrous customer responses and sub-10 mpg economy, were quickly recalled to the factory and converted to back to carburetors.
At the same time, across Detroit GM and Chevrolet were having much more success with their MECHANICAL fuel injection system on the Corvette V8 small-black and a few other Hi-Perf models. These are legendary today but had lots of teething problems which GM was able to resolve.
At the same time in the aftermarket, Stu Hilborn in Southern California introduced a fuel injection system for drag racing. It's the lovely, stereotypical array of intake stacks that deliver direct, unrestricted flow to each of the cylinders. Here's a Hilborn injection setup for a 427 Ford engine. Notice this shows no mechanical pump like the Mercedes System above. The pressure comes from an electric pump mounted elsewhere.
In case you are wondering how the Hilborn system can be so simple, it's a ALL or NOTHING system. This injection system is basically idle OR full throttle. It cannot be driven on the street, practically or legally.
PERSONAL NOTE: Hilborn is a large, successful business still located about 75 miles from me. The company is now run by Stu's daughter Edris (shown below). We went to the same college circa 1970. I confess I made a point to try to meet her because even then I knew about her dad's fame in the drag racing world. But I haven't connected with her since, and this picture I found is the first I've ever seen.
Back to the fuel injection... as things evolved into the Sixties, US manufacturers focused more on carburetors, while many European companies were still playing with mechanical fuel injection. Here's the aforementioned SPICA system on an Alfa motor. Notice the similarity to the M-B system on the 300SL, though the Alfa pump is driven by a belt rather than a shaft.
Here's a Kugelfischer system on the front corner of a Ford V6 engine -- it was also used on BMW2002 ti, and Peugeot 504 models along with many others.
The downside of all these systems was the need for a high-pressure, engine-driven mechanical pump, multiple lines, injectors, compensators, starting (choke) systems, etc. Additional enrichment or leaning of the mixture could only be attained by fiendish cams, ramps, notches, etc in the mechanical pumping system, or by vacuum switches, valves and bleeds.
WATCHTECH NOTE: The complex compensation system dilemma is akin to the mechanical perpetual calendars that some of us enjoy -- just as it's hard to implement the Gregorian Calendar mechanically, so it is hard to tweak the injection system to suit all the irregularities in mixture DEMANDED by maniacal racers, Sunday drivers or emission-fearing regulators.
Here's the final, best mechanical system from Bosch, the CIS with feedback control:
ELECTRONIC FUEL INJECTION SYSTEMS
The industry asked itself "Could we apply more computer power and do a better job, having come a long way since 1958?"
Bendix in the USA played with it for a long time and finally threw their hands up and said We can't make money at this!
They sold their system off to ROBERT BOSCH who said Yes, we can make this work!
PERSONAL NOTE: This may seem like ancient history to some of you guys, but at the same time as the date stamped on this system diagram, I was writing the first Fuel Injection Diagnosis and Training Manual in the US aftermarket, and my head was deeply into this stuff. I'm summarizing today primarily from memory, and from flipping through one of my books where I am happy to see my name at the top of the list of contributors. You can buy one on ebay for $5 so it's apparently not considered a precious vintage item...
I think I will stop here before going into onboard diagnostics OBD systems.
My point is this - the EARLY injection systems had many troubles. At that time we were "engineering in the dark" under pressure of bean counters, regulators, racing governing bodies, etc. Over the past 50 years those cars worth spending money on (like a 300SL) have been improved by aftermarket solutions OR careful tweaking by devoted restoration shops. The less-beloved injection systems have died miserable deaths.
Is it better to have a dead stock original, a modified system, or a converted-to-carburetors engine?
Personally, because I already have enough grief in my life, I vote for avoiding these models entirely OR springing for the modified, enhanced fuel injection.
Cazalea
More posts:
Kraftstoffeinspritzsystem aka Fuel Injection
We had a little discussion recently about the SPICA fuel injection system in the Alfa Montreal coveted by Nicolas, and it motivated me to create a short post. I will try to explain how these systems work (or not) and why they are better than carburetors (...
Thanks
Thanks for this thorough summary. I recognize a lot probably because I lived in the US late seventies and later on late eighties and it brings back memories of 5he hot rods and the illegal drag races (even on base) Todays car technology is incomparable no...
Fuelie 'Vettes are fairly well known . . .
. . . but there were other GM vehicles outfitted with Rochester injection, including the '57 Chevy (saw one on the 10 Freeway in the '80s) and '58 Pontiac Bonneville. I didn't know about Chrysler's experimentation until several years ago. They must've bee...
. . . and, of course, you knew . . .
. . . this was coming. My money's on the Wedge ;-)
And I used to think developing these systems was tough!
Imagine writing technically-correct, rhyming lyrics to a drag race song sung by surfer dudes with no knowledge of what they were singing about ...
Dennis Wilson, the middle brother and drummer of the Beach Boys, was . . .
. . . both a car guy and a surfer. Brian Wilson has the songwriting credit for Shut Down , but I've gotta believe Dennis was the tech consultant. ;-) ...
Certainly a "Car Guy" in some respects
Sadly he was a very troubled man and took it out on everyone and everything, especially his vehicles. Extracts from a 1984 article in Rolling Stone "Wilson was famous for letting people crash at his house — when he had one. In 1968, Charles Manson and his...
“In 1956 Oldsmobile was experimenting with Rochester fuel injection, at the GM desert proving grounds but offered the Rochester triple-carburetor J2 option for 1957“
I also found some details on the Rambler version of the Bendix Electrojector system. In contrast to Chrysler’s 20 cars produced, Rambler built 6 unofficially and 0 officially. It wouldn’t start under 45-50° F because they had no scheme for cold start enri...
