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 Post subject: Re: Emulsion
 Post Posted: Wed Oct 20, 2010 10:38 pm 
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What the dip in RPM at the start all about?


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 Post subject: Re: Emulsion
 Post Posted: Thu Oct 21, 2010 9:15 am 
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The race was a Super Gas race, the dip is when the throttle stop comes on. Kind of disrupts things a bit.


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 Post subject: Re: Emulsion
 Post Posted: Thu Oct 21, 2010 2:24 pm 
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The part where it was on the stop was interesting also. It was nice that there really wasn't much of change in weather in the afternoons. That more than anything helped me get a handle on the T-stop setting.

We made no changes in the carb all weekend. I haven't posted the second days logs. The AFR leaned out a bit and I haven't looked hard enough to see how the weather may have caused that. It was a small change and gives me an additional opportunity to learn something.

I'm going to throw this tuneup in my Ultra 1150 for a start point and see how that works.


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 Post subject: Re: Emulsion
 Post Posted: Fri Oct 22, 2010 5:05 am 
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Bruce are your o2 bungs in the collector?
It looks like it's sipping some clean air.


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 Post subject: Re: Emulsion
 Post Posted: Fri Oct 22, 2010 8:47 pm 
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No Scott, the bungs are in a primary tube.

BTW, I have been checking plugs as we've gone along. They're looking better deep inside and the heat range seems to be right where it should be. I'm using NGK FR-5s gapped at .035. I've used NGK 5s in my last engine with similar compression before so I'm not surprised. That engine did not like 6s. I intend to try 6s in this engine, just to see.


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 Post subject: Re: Emulsion
 Post Posted: Wed Feb 16, 2011 8:52 am 
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I've spent some time reading Larew's book and reading and re-reading this thread. It all seems to be coming together now but, I haven't had that lightbulb moment. Or at least I don't think I have.

Chapter 5, Section 5, Air Bled Nozzles is where I have zeroed into. While aeration (emulsion) and it's effects are explained well it's taken shrinkers explaination in regular English to help. What confused me was that what Larew describes as the "nozzle" we refer to as the mainwell. I had pictured the nozzle as that orifice where the mixture entered the booster venturi.

Now to the point:

In my application my carby tune tends to run lean towards the end of the run, sometimes as much as one full point. Ex. 12.4:1 to 13.4:1. My e-hole tune is to utilize the top and third hole down on a 5 hole BLP block. This leaves two more down that I now run plugged.

Larew describes the emulsion well as having the same pressure or slightly below that of the atmosphere in the air horn at full throttle or maximum indicated horsepower. Further, he describes that e-holes below the mainwell fuel level will aerate the fuel with bubbles and carry it to the booster venturi. Also, those e- holes above the fuel level do not carry much fuel because, as shrinker said, it's like the wind whipping over waves in the ocean. It creates some spray that contains liquid but not much. Thus a lean mixture. There needs to be air entering the fuel below it's level at that time. Simply, air entering below the top of the fuel level rises towards the booster and carries fuel with it by easing the tension all liquids have. Therefore, a richer mixture occurs.

The above I believe describes the symptoms of my tune up. At max HP the fuel level in my mainwells has dropped sufficently to uncover all the e-holes I am using. This leaves the only fuel aeration occuring is that caused by the air whipping over the fuel level and it's resulting lean mixture. Thus, my lean O2 readings at the end of my runs at the strip.

So, would adding an e-hole at the bottom of the well actually richen the mixture at the top end? There are two holes I could use but, I'd start with the bottom one. The engine should tell me which I need to ultimately use.


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 Post subject: Re: Emulsion
 Post Posted: Wed Feb 16, 2011 6:21 pm 
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You can add an e-hole or you can lower existing ones. The results are different depending upon the flow coefficient of the 'nozzle'.. If you add an extra e-bleed you increase the amount of air entrained in the flow. As the volume of air is increased the velocity of the air increases creating a change in the flow. There are many different flow styles of emulsion, The common ones we are interested in are tiny bubbles, slugging flow, churn flow and finally the 2 different transitions of annular flow. Each of these flow styles occurs in that sequence as the velocity difference between the liquid and the air increases. I suggest you go to Wolverine tube inc's web site and download the engineering book 3 chapter 12. Their description of the different flows is adequate.
When you add an e-bleed you may cause the flow style to change at high CFM demand. This is especially more likely to happen if you run a larger main air bleed than necessary.

Fluids follow the rules of sequential jetting, that is that unless the downstream jet is 4 times larger in area the flow rate will be changed. Said another way, if you have a .030" MAB and less than 4 e-bleeds of .030" too, then your going to reduce the flow of the MAB. SO why do we have only 2 or 3 e-bleeds? Its because we actually need to use that 'rule'. We can use the effect of sequential jetting restrictions to control the air addition rate to the emulsion. Even though at low CFM it only uses the top e-bleed you need the effect of sequential jetting to make the air volume small enough to create tiny bubbles because of you force too much air in there at low liquid flow velocity you change the flow style to slugging very easily.
Here is a scenario, the CFM is such that only the top e-bleed is functioning, so now you have a strong sequential jetting effect, then the CFM increases and the next lower e-bleed functions. Now you have a weaker sequential jetting effect. That means that the air pressure in the air well has DECREASED. Its decreased because there is more outlet area from the air well (you have more e-bleed's functioning now). This reduction in pressure in the air well slows the flow rate through whatever e-bleeds are functioning and the bubbles are smaller. Great idea huh.
The pressure in the air well is partially related to the amount that can leak out via the e-bleeds. You can do all sorts of combination's of MAB and e-bleed sizing and e-bleed locations to change the pressure in the air well. Pressure in the air well is a separate issue to the bubbles in the main well.
If you think about all this stuff long enough you will see how changing the MAB or the main jet necessitates changing the e-bleeds as well,because when you go to a larger main jet you fill the well faster so the head of pressure in the main fuel well is greater so less air flows from the e-bleeds. If hotrodders want to chase the power they need to understand how the systems work. Just changing the Main jet is not tuning it's butchering. If you have to change the main jet any more than 3 sizes then you need to address these other issues as well. . If you change the main jet and dont see a corresponding change in AFR or fuel consumption rate then you have a problem elsewhere in the carby design. Each holley jet is an increment of very close to 4% flow change so you should see that easily on a Wide band as a 4% change in AFR. It should also be a 4% change all the way up the CFM range too. If you dont see that change its because the e-bleeds are not in balance with the main jet and the friction of the 'nozzle'. The e-bleeds are there for slight correction not to do the job of controlling flow.
Some billet block manufacturers would have you believe that you need all these e-bleeds, no you dont, you need the right number of them in the right vertical positions. All you do by using 5 open bleeds is create increased friction in the nozzle at high flow demands and self defeat the whole scene.

The single biggest factor in everything that happens in the systems after the main jet is the outlet position of the booster. Its the booster outlet position relative to the main venturi that is the most important factor in what depression is generated by the booster. So go pay attention to the vertical height alignment of your boosters gentlemen.

Friction.
There are other factors to consider as well, when you aerate a liquid you increase the friction factor, that means that the effect of wall friction and diameter is reducing the flow rate. Friction does this by reducing the pressure difference from the start to the end of the pipe. In other words you loose pressure differential across the main jet. Its the difference in pressure across the main jet that determines the flow rate of the jet, so as friction increases because of too much air in the well, you go lean. To stop that you have to enlarge the well diameter, that changes the differential velocity between the air and the liquid flow and alters the transition point in the CFM range that the flow style will change.

You get your design into trouble when you try to make the range of operation of the venturi cover too great a CFM change. The solution to that is to add more barrels that come in at higher CFM. eg vac secondary or spreadbores etc. But the marketing gurus stuffed it all up and sell the wrong carbys. Then tuners go and jet the secondaries to a different mixture than the primaries and its a mess.
You can make just as much power from a 750 as you can a 1000 provided you configure the 750 correctly, if you look at the manifold pressure and compare the differences in pressure from a 750 to a 1000 CFM carby etc then think about why you’re not getting a corresponding change in power with the larger CFM. Its all about efficiency of combustion not air flow. There is no point having air flow without efficiency of combustion. You cannot prepare a 1000 carby the same as a 750, for a start you cannot use the same booster.
Correctly configuring either size may not be achievable to perfection, if you have the wrong booster forget it, Drag Racers think these issues don’t matter but their wrong, the limited range of CFM that racers use down a drag strip makes accuracy of everything more important. When the carby is larger to obtain more manifold pressure the depression range of the booster changes. Larews book talks mainly about carburetion to the limits of venturi flow, that’s applicable to stockers and nice to drive to the shop cars but its not what racers want. Racers operate their engines over limited RPM and limited CFM change. The depression range in the main well is related to where on the curve the main jets coefficient of discharge is. If the air speed is slow through the venturi (in other words a large venturi at WOT ) the manifold plenum is filled effectively making good potential for lots of power but the low depression places the discharge coefficient of everything basically closer to the bottom end of the scale of Reynolds numbers. If you download a Moody diagram you will see how friction affects flow and how the flow changes dramatically at the low ranges The e-bleeds are to assist in controlling this position not force it into submission, its just a little helper in the design.
For instance if you alter the fuel flow rate into the bowl you alter the main jet inlet head of fuel thus altering the main jet flow coefficient thus altering the head in the main well thus altering the e-bleed effect and on and on it goes. So go and ensure that you have STABLE fuel pressure, just something else to do huh!

So after all that Bruce, read the first sentence again.


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 Post subject: Re: Emulsion
 Post Posted: Wed Feb 16, 2011 8:05 pm 
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With that in mind, what vacuum reading at WOT would you consider minimum for the average engine? I realize the better job the engine does at combusting the lower you could go.


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 Post subject: Re: Emulsion
 Post Posted: Wed Feb 16, 2011 8:14 pm 
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Holleys work well with 0.7". Going larger to get the vac lower can be done if the CFM range is small like a high stall convertor or 5 speed box etc. Holleys work well at between 0.7 to 1.2" manifold vac for engines with about 500 plus HP for street use. But everyones got their own opinions on this stuff.


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 Post subject: Re: Emulsion
 Post Posted: Wed Feb 16, 2011 8:42 pm 
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My E85 carb is running .6, however the converter stall is pretty high at 6400, trap RPM at 7400. I have not dyno'ed this engine, but being a 4" stroke 427 with 23˚ heads that flow around 300@.650 I can't imagine peak HP would be more than about 6800 RPM.


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 Post subject: Re: Emulsion
 Post Posted: Wed Feb 16, 2011 9:23 pm 
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See that engine combo with that head flow and all that 23 degree stuff going on will flow choke the cylinders. So the engine wont actually draw fully normal increasing amounts of air as the revs rise so its going to have an easy time filling the manifold as the revs rise. That makes the carby less an issue too.


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 Post subject: Re: Emulsion
 Post Posted: Thu Feb 17, 2011 2:29 pm 
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shrinker wrote:
The single biggest factor in everything that happens in the systems after the main jet is the outlet position of the booster. Its the booster outlet position relative to the main venturi that is the most important factor in what depression is generated by the booster. So go pay attention to the vertical height alignment of your boosters gentlemen.


I believe we touched on this somewhere before, is it possible that this is why a lot of carb builders use a small stepped banjo on a Dominator, to force the bottom to be the point of highest airspeed/lowest depression? It would make the position in the venturi, at least within a small range, less important.

And I still think that in Bruce's case as he is running a low compression engine on pump gas, the AFR is not completely indicative of the carbs flow curve as much as it is the ability to burn the fuel at lower RPM's, making it look rich at lower RPM's and leaner up top. Comments?


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 Post subject: Re: Emulsion
 Post Posted: Thu Feb 17, 2011 4:12 pm 
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jmarkaudio wrote:
I believe we touched on this somewhere before, is it possible that this is why a lot of carb builders use a small stepped banjo on a Dominator, to force the bottom to be the point of highest airspeed/lowest depression? It would make the position in the venturi, at least within a small range, less important.

The pressure at the outlet of the booster when correctly done is due to the size of the main venturi not the size or design of steps etc of the booster. The main venturi size determines the depression at the restriction point of the main venturi. The correct placement of the booster is to have the outlet of the booster slightly above the minimum restriction point of the main venturi. When its done that way the booster material does not reduce the area of the main venturi thus maintaining CFM capability.
A correctly designed venturi has near perfect flow recovery. Flow recovery is the relationship of how much flow passes through the venturi compared to if it was just a straight pipe. So if you use a correct main venturi with correct entry and exit angles and then place a correct booster above the main venturi with the boosters outlet sufficiently close to the maximum depression point of the main venturi then you will achieve a higher depression at the restriction point of the booster than the depression measured in the main venturi. By using a booster this way you can generate enough lift to raise the fuel and flow it into the engine at a lower CFM than would be required by using just the main venturi depression. The booster does what its name is, it boosts the depression at a given CFM compared to what would be achieved in a simple single venturi alone.
So a possibe design situation is this, you can build a correct main venturi so that you get maximum CFM for the overall package of the carby etc then you can use a booster of any efficiency and shove it on top of the main venturi without causing any effect to the CFM of the carby. The booster just has to have sufficient amplification to lift the fuel at CFM point that you want mains flow to occur at. So the design of the booster is not so important but if you use a poor design with a lower flow recovery then you will get less amplification from it.

Say your starting to develop your own carby and you use a poor booster and you want to start the mains flow earlier than what your first prototype is currently working at, then you have to lower the outlet of your junky booster closer to the depression point of the main venturi. The closer you get the outlet of the booster to the maximum depression of the main venturi the greater will be the depression within the booster. If you put the outlet of the booster 10mm above the depression point of the main venturi you are asking the booster to amplify a weaker 'signal' point. So if you do that and then decide that you want more booster 'signal' you can either change the shape of your booster or make the booster waist smaller or add more 'tail ' to it so it gets closer to the max depression of the main venturi.
However if you shove the tail of the booster exactly at the maximum depression of the main venturi you disrupt the entrance flow patterns of the main venturi and you lose CFM and cause disruption to the discharge coefficient across the CFM range of the main venturi. If you stuff up the entrance to the main venturi this way you dont get smoothly increasing acceleration of the entrance air so your booster amplifies an erratic signal. Then you create erratic pressure fluctuations in the main well and thats the start of erratic AFR etc. So you go chasing e-bleeds and all that junk and get totally cheesed off and chuck the whole thing in the bin.
Technically the skirt on the bottom of the booster is disrupting the flow lines of the main venturi entrance. The skirt turns the flow outward where as its normal direction at that point is inward. If there was no booster at all the flow would be inward towards the center line. The air is converging toward the center and accelerating all the way and the absolute pressure is graduated lower toward the center line of just a main venturi without a booster above it. So when you shove a booster there you disrupt that to some extent, then if you add a skirt to the outside of the booster you really disrupt it.
The result of the skirt is that the signal stability to the main well is erratic. The skirt is just a cheap junky bandage for a design where they should have fixed the booster and the metering block. Marketing people get hold of the idea and rave on about how it cones the fuel and they take fancy pictures of blurred fuel droplets and talk about increased 'signal' but dont tell you that its stuffing up the AFR stability.
Carbys are capable of extremely fast response to air flow changes, there faster than an EFI system, I have tested response times of identical engines with both EFI and carbys, carbys correctly design with none of this junky holley cheaparsed manufacture shortcuts blow off EFI . The power output with a carby can be nearly double EFI in the first few combustions after a WOT snap. So using a correct booster is far better than skirting it because the last thing you should do is make a carby respond like EFI. Carbys need good design to be a stable AFR delivery platform, they dont have Feedback control like EFI does, so they rely on nature getting it right at the start and nature will follow its rules accurately if you set in place the right rules. Get lazy with natures rules and it has a way of coming back and biting you.

jmarkaudio wrote:
And I still think that in Bruce's case as he is running a low compression engine on pump gas, the AFR is not completely indicative of the carbs flow curve as much as it is the ability to burn the fuel at lower RPM's, making it look rich at lower RPM's and leaner up top. Comments?

i couldnt agree with you more. Wide bands are hopeless at getting the AFR right especially when the combustion is low efiiciency. Never believe a WB without first analyzing combustion efficiency with a gas bench.


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 Post subject: Re: Emulsion
 Post Posted: Thu Feb 17, 2011 9:28 pm 
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I don't have to worry about my WB this weekend as it appears to have taken a dump on me. I was going to do some carb testing today using some things discussed here yesterday.

shrinker, thanks for your recent replies.


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 Post subject: Re: Emulsion
 Post Posted: Sun Feb 20, 2011 2:06 am 
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Download this research paper on effects of air-bleeds on carburettor performance.
http://www.journalarchive.jst.go.jp/jnlpdf.php?cdjournal=jsme1958&cdvol=11&noissue=46&startpage=691&chr=en


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