KCS

iTrader: (20)

I have been discussing with others recently about the advantages/disadvantages of carburetors and EFI. One point that came up was that carbs atomize fuel better than EFI. Apparently Warren Johnson said this. I don't totally agree with this, but I don't necessarily think it's completely untrue.

I find it hard to believe that a fuel system operating at over 45 psi, cannot atomize the fuel better than a carb with just a few psi of pressure differential.

I would venture out to say that if it were true, that the key is either in the carb's ability to emulsify the fuel better, or that the draw in the booster is that much greater than the actual main venturi.

Anyone have any thoughts or comments? What influences atomization of a given fuel of the same density, specific gravity, etc.? Is there even enough accuracy in this testing to validate conclusive data?

Steve Bryant

iTrader: (1)

Multi-port fuel injection will atomize fuel better and more consistently by far as compared to a carburetor in my opinion. Direct injection will be a step better than multi-port injection. In some cases, throttle body injection is probably not much better than a carburetor when it comes to atomization.

The main advantages of a carburetor are simplicity and familiarity.

Steve

gametech

iTrader: (1)

I would venture to say in most cases throttle body injection isn't much better (if any) than carburetors. I don't mean because of design, but because of actual implementation. Historically, most TBI setups are junk.

jRaskell

iTrader: (1)

Any time someone injects a comment or statement made by a celebrity expert (and by celebrity, I only mean well known for his field of expertise) into a discussion, the first thing I always wonder and ask is, WHEN was said comment or statement actually made?

Warren Johnson has been around for a long time. Things that were true several decades ago may not be true today. Statements made several decades ago wouldn't necessarily be made today.

Schwanke Engines

iTrader: (1)

I guess I wound agree with jRaskell, you need to know the timeline. You have to think of it this way, if a carb is better, then why hasn't a production car had one on it for 20 some years?
I don't see where a carb could possibly atomize the fuel better than something running at 4 times the pressure. Maybe it mixes with more of the air because it is upstream, but then it takes up air volume and kills air flow?

NJSPDER

iTrader: (2)

TBI set ups do have some advantages in that they keep the consistency of the wet flow system, like a carb.

one of the double edged swords of port type injection systems is that they can take massive advantage of air density. this is great when the air is great and is a property that can be programmed to make max power on days when the air is less than ideal. the issue is consistency over the course of a day and evening at teh track.

wet flow systems can be much more forgiving(not sure if that is the right word to use) when conditions than dry flow. they tend to absorb changes in atmosphere a bit more before hitting that swing into amazing performance between rounds. this is a huge advantage of carb/tbi systems to many weekend warriors around the country.

wet flow works because any form of fuel is evaporative. this stabilizes not only the temperature of the intake charge, but also the humidity in it. this rreduces the difference between outside air densities and those that exist inside the intake manifold.

there are companies and racers playing with what cna best be described as long runner injection systems. think of something along the lines of an old school tunnel ram, with a pair of TB's on top and the injectors mounted as close to the carb flange as they will fit. the result is that you still have all the advnatages of digital fuel and ignition control, while still having the stability of a wet flow manifold.

being from new jersey i am lucky enough to see a few weekends a year that all this theory hits the ******* and the DA drops so low that you could make serious power running your engine on budwiser. you hear terms like "mine shaft" when the DA hits -1500ft

1 FMF

iTrader: (1)

my comment is more of a tangent than an answer.
with what little i know about fluid dynamics and the premise of an engine is nothing more than an air pump the way i picture the comparison is:

efi - where fuel is sprayed directly before the valve via injector (multi-port fuel injection) the advantage is near equal mass air to every cylinder provided the intake manifold design and manufacture is good. All there is is air flowing through the intake. advantage is with a good large throttle body and good intake design you can get minimal air flow losses and have the potential for huge airflow into the engine. And with equal airflow you can get optimal tuning (emissions, economy).


carb- fuel is mixed into the airstream as it passes through the carb. Disadvantage would be the obstruction of the airstream so one would think you would never get as much potential air flow into the engine as an efi setup, juggling the size of throttle body versus carb.
But, when fuel is mixed into the airstream prior to entering the intake manifold, an air/fuel mixture is much more dense than just an airflow. Can a carb setup, properly sized, give more volumetric efficiency at high rpm?
With an air/fuel mixture being more dense and when flowing at high speed (at high rpm) can you get more cylinder filling capability from momentum compared to an efi setup in which just air basically flows into the cylinders? This would also have to take into considering a good cylinder head and cam grind and only considering maximum power output. Chevy Hi-perf magazine has done some articles of LSx dynos that were carb setups and I thought I remember they put out power nearly equal that of a stock efi LSx. The disadvantage with the carb setup is keeping the fuel atomized in the airstream as the intake runners make tight turns and also keeping equal distribution to all cylinders, but doesn't the single plane high rise intake take care of this (again only concentrating on maximum power output, forget low rpm performance and emissions) ?

I feel pretty certain stating the carb is no longer used on production vehicles because of emissions and fuel economy. A carb cannot be tuned or operated anywhere near an EFI computer ignition system to maximize fuel economy and emissions. But if you consider those things irrelevant and if the only thing that matters it maximum power output, which inherently means maximum torque at the highest possible rpm, does the carb have a chance if you size things right? Everybody thinks only single 4-barrel, how about 8 individual downdraft carbs? For sake of argument, there's no external dimension restriction like engine bay & hood clearance, the engine is on a dyno in a big room.