Cant we invent carburetors that atomize fuel as good as fuel injectors by now?

[nascarnation]

Been too long since I looked at any of this stuff...

On a carb, at idle or off idle, isn't the fuel going in after the throttle blade? The boosters above the plate are in action for large openings, right?

I have to ask as the one time I looked down at a running TBI setup, I realized that it was squirting right at the plate, and basically turning back into liquid gas. Maybe that was a poorly running setup (probably was, it was quite old) but the picture has stuck with me since. Seems like TBI gets better fuel control but not necessarily better mixing.

On grasswaymotorsports(?) there was a poster who claimed to be at GM back in the day; he stated that the only reason they went to TBI over Quadrajet was because of NOx. The carb was better on all other fronts. I can't validate that claim but mentioning for completeness--TBI was a speedbump as port injection was always better. TBI was just cheaper and easier to changeover from a carb setup.

Carbs, with all their component parts and required fine tolerances were a manufacturing problem. The TBI eliminated so much of that. It was easier to manage software calibrations than mechanical complexity.
Instead of building and managing the production control of dozens (sometimes hundreds!) of variations of a carb model you were building and installing one basic injector unit.

Same thing happened with automatic transmissions. Instead of manufacturing dozens of different valve body configurations with specific springs and valves and orifices, you have a basic hardware set and manage the electronic calibrations.

 

[97prizm]

Carbs have no problems with atomizing fuel, that's a common misconception. Motorcycles probably took the cab tech the furthest and when many models switched to FI they actually lost HP and we started seeing choppy throttle and unpredictable response.

But FI is much better for emissions and fuel economy, so naturally manufacturers dropped carbs.

This is one of the ways you can spot a US spec 1990 Countach. The euro spec continued with a carburetor but due to tightening emissions Lamborghini installed Bosch K jetronic fuel injection on the US version.

 

[Bladecutter]

Technophobia strikes again, and creates a thread about wanting to go back to the good old days of carbs.
No.
Just no.

The whole point of going to port injection was to get the fuel injector as close to the intake valve as possible.
One fuel injector for each cylinder provides cleaner emissions, and more power.
Better cold start performance, and better high temperature operation.
ECU can adjust the mixture for changes in altitude and air density.

So many advantages for fuel injection over carbs.

 

[Mechanician]

Technophobia strikes again, and creates a thread about wanting to go back to the good old days of carbs.
No.
Just no.

The want to go back to simpler times isn't the answer most of the time.
I always think of how complicated indoor plumbing is.
Pipes that can leak, pipes that can plug up, all usually in walls or under concrete, and there's the water bill every month for most people.
With an outhouse, and a bucket, you won't have any of those problems.

 

[CorvairGeek]

Carbs are fuel dumpers, especially Holleys. The Q-Jet was a great carb for driveability...
A carb might equal or beat FI on the Dyno, but that's at full power.

I need to get my Oldsey's 4-Jet rebuilt; there aren't many great rebuilders left. Lars wouldn't do it for me. Kudos if you know who he is...

I love carbs. I have one of the last unmolested Q-Junks on the shelf.

Your Olds has a Quadrajet? I thought they were all the old Rochester 4 barrel until '66?

EDIT: I see now I think you meant the old Rochester 4 barrel. My misunderstanding.

 

[SubieRubyRoo]

Atomize? Yes. Control the amount and exact timing? No way.

You can’t avoid wetting the intake ports either with a carb. This is another big reason why carbs aren’t quite as “clean” on tailpipe sniffing. Liquid fuel doesn’t burn well.

 

[JimPghPA]

Cooling the air in the compression chamber allows higher compression ratios and leaner mixtures resulting in more available hp and and MPG. Cooling the air before it is inside the cylinder can't accomplish the same total amount of cooling, because that cooled air being in the intake manifold ends up getting some heat transfered into it by those passages, and valve(s). Also, the fuel vaporizes better when exposed to the high heat of compression, though the pressure is somewhat working against this (I think, but might possibly be wrong about that).

Total result, spraying fuel into the cylinder cools the air and fuel mixture better resulting in the above advantages.

Throw turbocharger into the whole thing and the very significant increase of compression temperatures, and DI really starts to look like a great idea.

Just run some good "complete fuel system cleaner" with a good amount of PEA in it, like Red-Line SI - 1 once in a while and you should be OK.

 

[JimPghPA]

You can’t avoid wetting the intake ports either with a carb. This is another big reason why carbs aren’t quite as “clean” on tailpipe sniffing. Liquid fuel doesn’t burn well.

Wetting the intake manifold results in cooling that intake manifold when that fuel vaporizes. That is cooling that does not happen on the intake air. And that is a big deal when your trying to keep the air / fuel charge cool so you can use high compression.

 

[JeffKeryk]

Your Olds has a Quadrajet? I thought they were all the old Rochester 4 barrel until '66?

EDIT: I see now I think you meant the old Rochester 4 barrel. My misunderstanding.

I think the full size BB cars got Q-Jets in 65 or late 65, not sure. I put an Edelbrock manifold and decent Q-Jet on temporarily. Sorry I ever did it. My car is a 97K survivor. It's perfect.

 

[emmett442]

Carbs, with all their component parts and required fine tolerances were a manufacturing problem. The TBI eliminated so much of that. It was easier to manage software calibrations than mechanical complexity.
Instead of building and managing the production control of dozens (sometimes hundreds!) of variations of a carb model you were building and installing one basic injector unit.

Same thing happened with automatic transmissions. Instead of manufacturing dozens of different valve body configurations with specific springs and valves and orifices, you have a basic hardware set and manage the electronic calibrations.

TBI eliminated none of that. There were adjustments to be made in both systems. TBI was still a function of the venturi, just like a carb. The injectors were above the throttle plates.

BUT TBI made the adjustments automatic. All did was eliminate throttle plate (idle speed) and mixture screws. A dynamic system able to adjust for abnormalities. Rather than using a screwdriver, the computer worked servo motors. But the end result was the same.

Not until port injection was there a real, functional difference. And under ideal conditions, the carb can even best that. It's Achilles heel is that it cannot adjust for environment where FI can.

 

[ecotourist]

The ubiquitous 1" spacer.

It can provide a more even "smoother" signal to the carb at low RPM when you have lumpy cam

Yes that's the right idea but more like a 4 - 6" deep spacer. That's how their carburetors ended up above the hood line, and many hoods on hot rods ended up with large holes in them. And of course many hot rods had no hood at all.

I have always thought that much spacer must have reduced the throttle sensitivity. But with high air + fuel flow rates perhaps not as much as I imagined.

 

[SammyChevelleTypeS3]

I know history has erased the Motorcraft variable venturi carb but I had one one a land barge Ford Country Squire station wagon I think in the early 80's. It was a company car and On the highway that thing would get over 32mpg with a 302 v8. I heard of people getting 50+ mpg in the smaller cars with that motor and carb . That was an amazing combination since it performed flawlessly and returned great performance and mileage.

Those Motorcrafts were really good ones in its day and was used a lot by Ford on their smaller cui engines. The 302cui engine was one of the best / popular engines Ford has put out. Ford produce many of the carb models and then kept on with the 302s into the EFI ones that actaully caused the rebirth of the Mustangs.
The last 302cui Ford engine I had , EFI type in a F150 was one of the absolute best engine I have owned. My 302s never were known for great mpg but carbs or EFI they all ran great with never an issue.

 

[ecotourist]

Seems to me the BMW 2002 Tii (which was considered a hot car in its day) had mechanical fuel injection.

But the BMW 2002 Ti (a European spec) had a carburetor. And it was even hotter. I've only driven one and it was quite a ride.

 

[oil pan 4]

True, but I bet that 6L 'burb meets current emissions regulations while the leaned out carb might not meet requirements for its year of manufacture (maybe it does, if it's a 3/4T with the looser standards).

Obviously it was making tons of NOx. For about 99% of the land area of the United States NOx emissions are irrelevant.

 

[The motor guy]

The carb on my commercial mower is like ice cold when running. Or part of it is. I just can't remember the name at the moment. I think it's the part between the engine and the carb where it all gets mixed together

 

[SC Maintenance]

Even if you could build a better carb it would be of no value. The huge benefit of EFI is that the ECU can instantly add or remove fuel via a simple pulse width. Short and long term fuel trims ensure a perfect burn near instantaneously in almost any conditions, and in order that they are useful, you need a fuel injector - the closer to the burn point the better.

Atomizing fuel really isn't the issue.

 

[factorytuned2012]

how about an old

Bendix-Stromberg pressure carburetor​

 

[barryh]

A carb can't adjust for varying barometric pressures and temperatures like FI can.

Not for temperature but CV carbs for the most part do automatically adjust for changes in barometric pressure as lower air pressure due to altitude will lift the needle less. So on the main circuit CV carbs are fine at altitude. Fixed jet carbs and the pilot/idle circuit of a CV carb do not compensate for changes in air pressure.

 

[fdcg27]

It seems to me that any carb must adjust for ambient air pressure changes seamlessly, since each intake stroke draws in a fixed volume of air and air at lower ambient pressure will have less mass for that volume, with therefore less pressure drop to draw fuel out through the jets.
Tell me where I'm off base on this.

 

[Mechanician]

It seems to me that any carb must adjust for ambient air pressure changes seamlessly, since each intake stroke draws in a fixed volume of air and air at lower ambient pressure will have less mass for that volume, with therefore less pressure drop to draw fuel out through the jets.
Tell me where I'm off base on this.

Agreed there are some automatic adjustments built in. Don't forget the lowered air pressure on top of the fuel in the float bowl - pushing the fuel through the jet.
But none of this is as accurate as an electronically controlled, closed loop system, like a modern fuel injected engine.