And now add to it the proliferation of turbocharging in mass produced engines. Carbs struggle with forced air induction. FI lends better to tuning for power and efficiency across various RPM ranges.
Cant we invent carburetors that atomize fuel as good as fuel injectors by now?
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Webers just look so freaking cool, though.Motorcycles used CV (constant velocity) carbs for years and I believe there are still a few models that may have them (Suzuki DR650 for example). They have a variable venturi and do provide better control over the air/fuel ratio than conventional fixed diameter venturi carbs.
I don't know that I noticed any massive gain in MPG with them. I did notice a decrease in throttle response when compared to a conventional carb. We would try all sorts of tricks to make the vacuum operated slide (variable venturi) pull up or open faster.
These carbs did not work well for hard core dirt bike riding, such as a dual sport bike ridden on a motocross track, as the slide's weight would 'close' the carb when landing from a jump. Causing the engine to lose power just when needed and when traction was highest.
I converted my KLR600 from a Mikuni CV carb to a conventional Del'Orto pumper carb of the same size. The difference was remarkable. The variable venturi carb was not ideal for good performance.
Back in college, I had a '66 Mustang with downdraft Weber carbs. They worked really well with stunningly great throttle response, they would ice up though. MPG was acceptable, and peak power was on par with a single plane intake manifold and big Holley carb, with much better low end and no bogging. Today, the setup is again popular, and my old college roommate's brand new 347 cubic inch Ford small block makes a solid 550+HP.
EDIT: I guess my point is that such carb setups can be designed to provide even fuel distribution for each cylinder. And/or can be designed to provide excellent atomization. 2 strokes often use very crude carbs with great results. The air/fuel movement through reed valves, around the hot crankshaft, and through hot transfer ports helps with atomization.
Hot rodders used to put a raised section between the carburetor and the intake manifold. I assume the idea was to provide better fuel air mixing. But it raised the carburetor which then interfered with the hood.
I see and smell too much of that. Out of the box, untuned, junky Edlebroke replacement carb with the choke only half open. Factory air cleaner and heat stove tossed, Vac advance plugged or not working on the distributor. Running on seven of eight cylinders. I could go on for days.
To the op, annular booster carbs help atomisation, but the intake manifold and cold running temps can wreck it again
Yup. If you had a Shinto master tuning the thing every 500 feet altitude increments and it was in hot weather, you could eke out a few HP over the injected rig.
The ubiquitous 1" spacer.
It can provide a more even "smoother" signal to the carb at low RPM when you have lumpy cam
Carbs have a maximum of 15 psi (atmospheric pressure) to break the fuel into droplets. Port FI is tens of lbs of pressure, GDI is hundreds of pounds. Carbs also have an inertia problem on rapid throttle change where, the air flow can respond almost instantly but the more dense fuel will lag behind matching the air. Thus the need for accelerator pumps and idle dashpots.
When I got my first car with just TBI I couldn't believe it ran just as good with a cold engine as it did when hot.
When I got my first car with just TBI I couldn't believe it ran just as good with a cold engine as it did when hot.
Plus most users care more about driveability than max HP. I know I gladly sacrifice some power if it means it just goes always under any conditions
I believer Thunderhead289 (that's his youtube name) sells his "carb cheater" with closed loop feedback. Use an O2 sensor and a servo to somehow adjust carb tuning screws on the fly--I think that is the concept, but since I have no plans to go and own an old car, I haven't dug into it more. No idea how well it works.
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Different length runners have different "resonance frequency", better for performance at different RPM.
Thus the variable length intakes used on some modern fuel injected engines, to squeeze out all possible power across the range.
This is another example of why, if simply installing a different air filter was worth the effort, they would do it themselves.
The different length runners to the cylinders from a centrally mounted carb, or injector, isn't near ideal.
The mixture can't be maintained constantly to all the cylinders.
Any "straight" cylinder arrangement, like an old 6 cylinder, is even worse.
The old Hot Rod raised intakes were a crude solution to help this problem.
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.
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.
Yes. We "could" do lots of things but the real question is "should" we do those things. Unless it really pays off somehow the answer is no.
Interesting
A self tuning & closed loop carburator
I think that's called TBI
I'm intrigued by this product for tuning older normal carburators properly, as no one around me has a gas analyzer or the know-how to use it
The propane enrichment method (Mopar) needs the analyser, and I need to brush up on using a vacuum gauge to do it
GM invented the "self tuning feedback carburator" many decades ago
It was called Computer Command Control, and I've had to learn far too much about it against my will
Mine will run right, some day
Pulse width modulating the mixture control seemed to be the last hurrah of the carb in passenger cars
Been too long since I looked at any of this stuff...Interesting
A self tuning & closed loop carburator
I think that's called TBI
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.
Didn’t mean to I imply that carbs don’t work well, they do, and worked well for over a century, but it’s a lot easier to get fuel to atomize with that higher pressure spray on a fuel injection set up, and that was the original question.
For a while, carbs still flowed more air than contemporary FI set ups, and I’m thinking of the original GM TPI, their first “performance” multiport injection system, that was flow restricted. If you wanted to build more power on a mid to late 80s small block Camaro, for example, you bought a carbureted car, not the “TPI” performance model.
Intake charge cooling and ultimate vaporization through the entire intake tract is another matter. TBI did well with both.
The precision with which fuel could be metered, as well as the ability to work under positive and negative “G”, is why FI was developed for race cars and fighter aircraft a long time ago.
Cost is why carburetors continued on regular cars, and to some degree, regular aircraft, long after FI was developed.
For a while, carbs still flowed more air than contemporary FI set ups, and I’m thinking of the original GM TPI, their first “performance” multiport injection system, that was flow restricted. If you wanted to build more power on a mid to late 80s small block Camaro, for example, you bought a carbureted car, not the “TPI” performance model.
Intake charge cooling and ultimate vaporization through the entire intake tract is another matter. TBI did well with both.
The precision with which fuel could be metered, as well as the ability to work under positive and negative “G”, is why FI was developed for race cars and fighter aircraft a long time ago.
Cost is why carburetors continued on regular cars, and to some degree, regular aircraft, long after FI was developed.
Interesting
A self tuning & closed loop carburator
I think that's called TBI
I'm intrigued by this product for tuning older normal carburators properly, as no one around me has a gas analyzer or the know-how to use it
The propane enrichment method (Mopar) needs the analyser, and I need to brush up on using a vacuum gauge to do it
GM invented the "self tuning feedback carburator" many decades ago
It was called Computer Command Control, and I've had to learn far too much about it against my will
Mine will run right, some day
Pulse width modulating the mixture control seemed to be the last hurrah of the carb in passenger cars
No, TBI has an injector in the throttle body.
Feedback carburetor, like the Q-jet, relies on Venturi effect to get the fuel into the airstream at the throttle body.
The tuned port injection on my 86 and 90 Corvettes was so easy to start and ran flawlessly. They also ran outta steam over 4500 rpm or thereabouts. The cam was optimized for that range.
Properly setting up the Q-Jet on my 68 to run this well takes some doing and is far more finicky reacting to the weather.
Properly setting up the Q-Jet on my 68 to run this well takes some doing and is far more finicky reacting to the weather.
I was able to get 16 to 18mpg highway with carb on my 3 speed auto 454 suburban turning for lean burn with a wide ban O2 sensor with gauge. 20 years newer fuel injected 6L engine suburbans running 4 speed auto with lockup and egr wouldn't even get that. So it would appear that carbs atomize fuel just fine.
I would tune mine for lean burn with a wideband O2 sensor with gauge. It was cheating. Its exhaust smelled like firecrackers. No catalytic converter.
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).
