Re: Fuel atomization: Carb vs. EFI
[Re: hemienvy]
#2724754
12/17/19 11:33 AM
12/17/19 11:33 AM
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Joined: Oct 2007
Posts: 4,212 New York
polyspheric
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Full atomization?
The "technology" to produce any size droplet is now over 100 years old. As I said - is that what you want?
Boffin Emeritus
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Re: Fuel atomization: Carb vs. EFI
[Re: polyspheric]
#2724946
12/17/19 10:00 PM
12/17/19 10:00 PM
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hysteric
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Full atomization?
The "technology" to produce any size droplet is now over 100 years old. As I said - is that what you want? Which technology was that?
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Re: Fuel atomization: Carb vs. EFI
[Re: hysteric]
#2724968
12/17/19 10:35 PM
12/17/19 10:35 PM
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hemienvy
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Polyspheric, I find your posts excellent and informative, but I do not understand your question here. Why would it be desirable to have poor fuel atomization ? The more vaporized the fuel, the more complete the combustion, unless of course the mixture is stoichiometrically rich.
Last edited by hemienvy; 12/17/19 10:42 PM. Reason: I goofed
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Re: Fuel atomization: Carb vs. EFI
[Re: hemienvy]
#2725066
12/18/19 10:18 AM
12/18/19 10:18 AM
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polyspheric
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The fully atomized fuel displaces its equivalent volume of air in the charge mass; gasoline as a gas is many, many times larger than as a liquid. In engines with poor breathing (DV was specifically referring to the BMC Mini) air is more important. A hemi would have the opposite argument: large intake port means fuel drop-out may occur if they're too large.
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Re: Fuel atomization: Carb vs. EFI
[Re: hemienvy]
#2725160
12/18/19 04:28 PM
12/18/19 04:28 PM
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HotRodDave
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The fuel in MPFI is injected onto the back of the valve while it is closed so the fuel is the first thing in as the valve opens. Think of it like putting cream in your coffee, if you add the cream to your cup first(small amount) then add the coffee(larger amount) then just the act of pouring the coffee in will mix it all up and you don't need to stir it at all, on the other hand you pour the coffee first then squirt in the creamer you are gonna have to stir it because it won't mix on it's own.
Carbs on the other hand spew the mix in the chamber at the same time, it also has more time in the runner to evaporate a little more or for the fuel to seperate out if the manifold or port is poorly designed.
EFI also comes out at a much higher pressure and this also helps to atomize so 6 of 1 or 1/2 dozen the other way.
Direct injection is more about MPG and emmisions than power or even atomization, it allows the whole combustion chamber to filled with a homogenious mix under WOT or more importantly, part of the chamber can be filled with a real good mix near the spark plug while the rest is just air, this minimizes heat rejection into the metal because the air acts like insulation, you can intentionally have lean and rich areas at the same time in the chamber to improve MPG and emmisions, this is not really utilized under WOT because a carb or port injection both can do a fine job of filling the entire chamber with a good mix.
In my personal opinion if MPG were the primary concern you would want all the fuel vapoorized and evenly mixed so you would want the high pressure fuel atomization of MPFI and a longer time in the manifold that you get from injectiing it at the beggining of the runner instead of at the valve, my TBI motors I have owned always got the best MPG, chevy, dodge both got better MPG with throttle body injection than MPFI magnum and vortech style engines at the cost of power.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Fuel atomization: Carb vs. EFI
[Re: MoonshineMattK]
#2725164
12/18/19 05:03 PM
12/18/19 05:03 PM
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AndyF
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Can anyone please explain how a carb atomizes fuel better than fuel injection.
For the sake of my question both the carb and fuel injection are tuned properly. I don't think anyone on this thread knows the answer to that question. That is a very complicated technical question and nobody would be able to prove it one way or the other without a lab full of equipment. A carb works opposite of injection so the behavior is totally different. In a carb the low pressure area in the venturi sucks the fuel out of the bowl. The pressure differential in a carb is only 5 or 6 psi while an injector operates around 50 psi. The metering block in a carb adds air bubbles to the fuel which helps. There is no air bubble system in an injector. If someone really wants to know the answer to this question they would need to talk to an injector engineer at Bosch. My guess is that they know how to measure it and and could explain it.
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Re: Fuel atomization: Carb vs. EFI
[Re: HotRodDave]
#2725170
12/18/19 05:15 PM
12/18/19 05:15 PM
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MR_P_BODY
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Thats the issue here... if you look at the question you can have 2 answers.. a injector by itself will atomize better but in a full system as in TBI you have a intake(mixer area) a MPI has higher pressure than a TBI and the MPI will atomize better EDIT I had 10 years of flowing injectors and building the flow stand
Last edited by MR_P_BODY; 12/18/19 05:31 PM.
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Re: Fuel atomization: Carb vs. EFI
[Re: MR_P_BODY]
#2725193
12/18/19 07:22 PM
12/18/19 07:22 PM
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Joined: Jan 2005
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HotRodDave
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Thats the issue here... if you look at the question you can have 2 answers.. a injector by itself will atomize better but in a full system as in TBI you have a intake(mixer area) a MPI has higher pressure than a TBI and the MPI will atomize better EDIT I had 10 years of flowing injectors and building the flow stand Aren't most of the modern retrofit throttle body EFI systems now running basically 8 MPI injectors bunched together and running high pressure (50PSI or so) and squirting it in the throttle body? Another benefit for modern cars is that a dry manifold can be made more effective at ram tuning and physically fitting into any given engine compartment than one designed to carry a mix of air with fuel suspended evenly into it. The beer barrel intake on a magnum or modern hemi is a perfect example, they have even length and shape from one runner to the next as well as a long length that would let fuel drop out at low velocipy. They would both have terrible distribution with a carb (either a down draft on a magnum or side draft on hemi).
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Fuel atomization: Carb vs. EFI
[Re: HotRodDave]
#2725197
12/18/19 07:35 PM
12/18/19 07:35 PM
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MR_P_BODY
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The last time I work with either system the TBI was 14# and multi point was 55#.. I started out flowing single injectors at multiple voltages and seeing the differences in the area around each zone of the flow pattern and the different duty cylcles/pulse width
Last edited by MR_P_BODY; 12/18/19 07:44 PM.
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Re: Fuel atomization: Carb vs. EFI
[Re: AndyF]
#2725272
12/19/19 12:33 AM
12/19/19 12:33 AM
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jcc
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Holley Sniper runs at 58 psi while Holley MPFI runs at 43 psi. Or whole factors of normal sea level atmospheric pressures.
Last edited by jcc; 12/19/19 12:33 AM.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Fuel atomization: Carb vs. EFI
[Re: Gavin]
#2725357
12/19/19 11:53 AM
12/19/19 11:53 AM
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Cab_Burge
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There's really no debate to be had on which technology atomises better. You've had at least two people who have worked in the industry say the same thing (Mr P Body and myself). Higher pressure gives better atomisation. EFI is ALWAYS higher pressure therefore, leaving the carb or injector, better atomisation, every time, period.
Per my original reply - what you do with it after that is getting a lot of good discussion here, but there's no uncertainty about which device atomises better. I am still in doubt about which system, EFI or a dual quad tunnel ram set up, is better for a all out drag race motor Hence NHRA Pro Stock not going faster now with EFI than they did with dual carbs on a tunnel ram intakes I remember several different mechanical fuel injector companies testing the location of the injectors heights in there all out race set ups for dirt and asphalt track roundy round all out race cars
Last edited by Cab_Burge; 12/19/19 11:54 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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