fuel systems

Factual Questions
1

okay… me and my boyfriend got into an argument about this one… i say carbureted cars do not have throttle bodies… carbureters were replaced with throttle body fuel injection systems… he says carbureted cars also had throttle bodies… he (of course) thinks that he is right, so i need some experts to prove him wrong. ya know… since i’m just a girl.

also… what were some of the last cars that were carbureted? he said that camrys- or some car similar was carbureted up until the mid-90’s… is that true?

2

When carbs were overtaken by throttle body injection (TBI) varied with the manufacturer. Tell BF to think of it this way: a carburetor is a means of regulating the amount of fuel which is finely atomized and mixed with intake air before being fed to the cylinders for combustion. A TBI unit is an efficient spray unit, so why have a carburetor and a TBI?

3

Of course they had throttle bodies. In fact, “throttle body fuel injection” is really an inferior type of injection. It’s basically a carb with a single injector instead of carb. jets. It let manufacturers sell cheap cars and advertise them as being fuel injected – yeah, okay, there was some benefit; it was computer controlled, specific amounts, and was better than traditional carbueration.

4

IIRC, the last cars sold in the US with carbs were Hyuandai’s and they switched to fuel injection in the early 90s. And carbs do have throttle bodies, however, the carbed throttle bodies are probably quite different than the TBI systems, so you could say that you’re both right.

And tell your boyrfriend that you should never argue with a woman, because you won’t win, and that if I’d listened to that advice, I wouldn’t be nearly forty and still single.

5

A throttle body is just the assembly that holds the throttle plate. Most of them are a casting with a round hole for the air/fuel mixture to pass through into the intake manifold.

To control the amount of air/fuel mixture (i.e. to throttle it), a movable plate fits into the hole. When the plate is in the same plane as the hole, it fills the hole and very little mixture gets through. When the plate is rotated on its side so it’s perpendicular to the hole and aligned with the direction of flow, the hole is basically wide open and you get maximum air/fuel mix into the engine.

Check out this link for pictures of a few different throttle bodies:

http://www.edelbrock.com/automotive/throttle_bodies.html

Carburetors have throttle plates just like throttle body injection systems. I seem to recall (it’s been almost 30 years since I rebuilt a carb) that some carbs had an actual separate throttle body that the main body of the carb sat on top of, and in some carbs the throttle body was simple the lower part of the main carb body casting.

Either way, the function is essentially the same. I’d have to go with the boyfriend on this one.

6

I’ve been in the auto business for way more years then I care to think about. When I first read the OP I thought, that the boyfriend must be a moroon, of course a car with a carb would not have a throttle body, then it occurred to me we are dealing with semantics.
To quote RJKUgly

In a carb the term is throttle plate, I don’t think I ever heard the term throttle body when referring to a carb, only an injected cars uses this term. The first use of the term throttle body that I recall was with GM TBI systems or Bosch K Jetronic both from the late 70’s early 80s.
Throttle plates are found on all gas engines regardless if they have a carb, or FI. Again on every carb I have ever seen the throttle is the lower part of the carb, not a separate part, late an injected throttle body is. The throttle bore, and butterflies may be bolted onto the bottom of the carb, but they are considered part of the carb, and if you buy a new or rebuilt carb, come already bolted on. For these reasons, I am going with the BF being wrong, and krystalkf being right. Not because of carbs not having a throttle, and a throttle bore, but because of the common usage of the terms.

7

Perhaps this is an issue of semantics. When I speak of a carburetor, it is a mechanical device, excepting electronic components such as dithering solenoids and a bimetal choke control, and it can operate absent all electronic interface.

The same can’t be said for those TBI units to which I’ve been exposed.

8

I thought I could remember some carbs that had a separate casting that held the throttle plate, but I could very easily be wrong. It has been a long time since I did much work on a carb.

I guess this is a question of semantics.

In regards to the throttle plate, the difference between carbs and TBI units is that the throttle plate assembly is only part of a carb. You also have the float, the bowl, the jets, the choke, idle jets, etc. Whereas with a TBI you basically have the throttle plate assembly and the Injector nozzle.

Thus the term “throttle body” describes a major component of a TBI, but doesn’t really apply as well to a carb (especially if it isn’t a separate component) because the throttle plate is a smaller part of the whole.

And as Rick says, the term “throttle body” is pretty much (possibly totally) confined to talking about TBI units.

Still, carbs and Throttle Body Injection units both have a component that looks pretty much the same and perform the same function in pretty much the same way. To me, this suggests that they both have that particular component, whether you call it a body, an assembly, or just a plate.

I’d still go with the boyfriend.

9

These answers are essentially correct, but I think fail to clear up the confusion behind the question.

All cars, injected or carbureted, have throttle plates (throttles).

As mentioned, in some carburetors the throttles are (or throttle is) in the main body of the carb. In others, they are in a separate detachable portion of the carb which is called a throttle body. This is the official correct term for that part of the carb, which can be seen in repair manuals and rebuild instruction sheets.

Fuel injected cars have their throttles in discrete throttle bodies, as obviously it’s not possible for the throttles to be in the main body of the carb.

NOT ALL FUEL INJECTED CARS HAVE THROTTLE BODY INJECTION.

The phrase “throttle body injection” – the complete phrase, all three words together – refers to systems where the injectors (usually two) are located in a housing just above the throttle body, delivering the gas in the same place a carburetor would. This is in contrast to “port fuel injection” (sometimes named differently, e.g. multiport injection, sequential injection, etc.) where there is one injector per cylinder, located in the intake port. This puts the fuel delivery closer to the cylinder, which is more efficient, which is why throttle body injection has been abandoned for port injection.

But again, even port injected cars have throttle bodies. What they do not have is throttle body injection.

So, some carbureted cars had throttle bodies, but they were a portion of the carburetor, not discrete units such as we see on injected cars.

Carburetors were replaced with fuel injection systems, but not necessarily with throttle body injection systems. The first electronic fuel injection (Bosch type) was port injection. Its prototype debuted in the 50’s, and the developed system was used on European cars in the 70’s (and maybe late 60’s). I didn’t see any throttle body injection until the 80’s, when the American manufacturers started designing their own fuel injection. During the 80’s and 90’s when fuel injection was becoming common, both throttle body injection and port injection were widely used.

We hear the term “throttle body” a lot more nowadays because fuel injected cars – both throttle body injected and port injected – have throttle bodies which are stand-alone parts, like fuel injectors and fuel pumps are stand-alone parts.

I believe the last carbureted car sold in the U.S. was a '90 or '91 Subaru Justy.

10

The factory service manual for my 1969 Chrysler Newport refers to a part of the carb as a “Throttle Body” so the term was in use before TBI units became common on cars.

11

And even diesel engines with direct fuel injection into the cylinder still have a throttle plate in a throttle body.

Now, the La’Rhone radial engine did not have a throttle body or throttle plate.

12

Thread drift, but this can’t be allowed to stand.

Very, very few diesels have either throttles, throttle plates, or throttle bodies. Mercedes, I believe, did at one time experiment with such to improve engine braking, but otherwise diesels never throttle the air. Only fuel flow is controlled.