Mr Tuner sir, Holley emulsion holes?

[Andereck]

Tuner,
I was hoping you could take the time to explain the emulsion "circuit" in a Holley metering block. Specifically how the holes position and size effects fuel delivery/quality and how the high speed bleed interacts with the process. I seek the fundamentals and would like to know when, if ever a change is warranted. I have both Holleys and a couple of Claws that have tunable metering blocks but just haven't dared. I have come close to replicating a Holley metering block on one of the Claws as they have a different area and position than the Holleys but just haven't yet as I've just been a puss.

Thanks in advance for any light you care to shine on the subject.

[Tuner]

Why didn't you ask a simple question?

In the thread “750 Holley carb help” Klaus made this statement, “On carbs it's very important that the correct two-phase flow gets established during emulsion. Otherwise you will see RPM dependency of AFR.” Thank you Klaus, but forgive me if I see your remark as a profound understatement. Incorrect two-phase flow is at the root of all this aggravation. People who have drill bits but don’t know why to use them have been molesting innocent carburetors for a long time. Now some of them are in charge of the manufacture of new carbs and they think they have improved them by using larger drill bits to make the air bleed and “emulsion” orifices. I guess the guys that engineered the original carburetors on the old muscle cars were pretty stupid or they would have “improved the emulsion” 40 or 50 years ago when they had their chance. After all, they had the awesome power of the single-point ignition system at their disposal, they shouldn’t have been afraid of a little soot.

It is well documented that introducing air into the main well encourages low signal flow and can encourage or discourage high signal flow. The natural characteristic of a plain jet and nozzle (no air) is to get richer as airflow increases. The purpose of the air bleed system is to modify that behavior to accomplish a constant (or the desired) air/fuel ratio over as wide a range of airflows as possible. The particular ratios for power and cruise are realized by the selection of jet and rod or jet and auxiliary jet (power valve channel). The purpose of air bleeds is not to emulsify but to accomplish the correct fuel delivery. Emulsion is just a beneficial side effect.

What I’m going on about here is Klaus’ remark about “correct two-phase flow”. That is the description of a fluid flow that is made up of a liquid and a gas flowing together in the same conduit. As the ratio of gas to liquid increases (more gas, less liquid), at some point the gas bubbles coalesce from many small ones into a few big ones and the flow starts to “slug” and become erratic. The carburetor nozzle spits like a garden hose with air in it when there is too much “emulsion” air.


An emulsion of air and fuel has reduced density, surface tension and viscosity compared to fuel alone. This increases the flow of fuel considerably, particularly in low-pressure difference operation, at low throttle openings or lower engine speeds. Just how much of an increase (richer) is dependant upon where and how much air is introduced into the fuel flow.

Mainly, what must be understood is that because the fuel discharge nozzle connects the venturi to the main well, whatever the low pressure (vacuum) is in the venturi, it is also the pressure in the main well. The air bleed is in the carb air horn or somewhere else where it is exposed to essentially atmospheric pressure, which is higher than the venturi pressure. This pressure difference causes air from the air bleed to flow through the emulsion system into the main well and to the nozzle. The flow of air can have very high velocities, approaching sonic in some orifices. The airflow literally blows the fuel toward and through the nozzle. A larger main air bleed will admit more air to the emulsion system and that can increase or decrease fuel flow to the engine. The size, number and location of the other air holes in the emulsion system, the size of the main well flow area, the size of the nozzle and the specific pressure difference at the moment are the determining factors. The ratios of air volume to fuel volume to flow area, with the air volume's expansion with the venturi velocity induced pressure reduction being the key. The bubbles expand as the pressure drop increases with airflow. Suck on an empty balloon to experience the effect.

The fuel flow through the main jet is the result of the pressure difference between the atmospheric pressure in the float bowl and the venturi air velocity induced vacuum acting on the nozzle and the main well. The venturi vacuum in the well is reduced (the pressure is raised) by the "air leak" from the air bleed. This reduces the pressure difference that causes the flow through the main jet. If the air bleed were big enough, the pressure in the well would be the same as in the float bowl and no fuel would flow. Think about drinking through a soda straw with a hole in it above liquid level. Bigger hole, less soda. Suck harder, not much more soda. Big enough hole, no soda. This is the means by which the emulsion system can "lean it out on the top end". Incidentally, the vacuum that lifts water up a soda straw is in the most sensitive operating range for emulsion systems.

It is in the lowest range of throttle opening, at the start of main system flow, that the effect of adjusting the introduced emulsion air (and it's effect in increasing the main fuel flow) is most critical. Small changes can have large and sometimes unexpected or counter-intuitive consequences. The goal is to seamlessly blend the rising main flow with the declining idle/transition system fuel delivery to accomplish smooth engine operation during opening of the throttle in all conditions, whether from curb idle or any higher engine speed. The high speed and load mixture correction is usually easily accomplished, in comparison.

The vertical location of the bleeds entering the main well influences the fuel flow in the following ways.

1: Orifices above float level or between the well and the nozzle allow bled air to raise the pressure (reduce the vacuum) in the nozzle and above the fuel in the well. That delays the initial start of fuel flow from the nozzle to a higher air flow through the venturi and is used to control the point in the early throttle opening where the main starts.

2: Orifices at float level increase low range (early throttle opening) fuel flow by carrying fuel with the airflow to the nozzle.

3: Orifices below float level increase fuel flow by the effect of lowering the level of fuel in the well to the hole(s) admitting air. This is like raising the float level a similar amount (increases the effect of gravity in the pressure difference across the main jet) and also adds to the airflow carrying fuel to the nozzle. Locating the orifices at different vertical positions influences this effect’s progression.

4: The "emulsion holes" influence is greatest at low flows and the "main air bleed" has most influence at high flows.

In the first three cases above, once fuel flow is established it is greater than it would be with fewer or smaller holes. Visualize wind blowing spray off of the top of water waves. It doesn’t take much pressure difference to cause the velocity of the airflow through the bleed orifices to have significant velocity in the orifice, even approaching sonic (1100 F.P.S.) if the orifices are small. The phenomena of critical flow is what limits the total air flow through an orifice and allows tuning by changing bleed size.

Essentially, the emulsion effect will richen the low flow and the air bleed size, main well and nozzle restrictions will control the increase or reduction of high flow. Again, the desired air/fuel ratio is the primary purpose of the bleed system. "Improved emulsion" is an oxymoron if the modification of air bleeds to "improve emulsion" results in an incorrect air/fuel ratio in some range of engine operation. Correct proportioning of all the different bleeds (and, of course, the idle, transition and power circuits) will give the correct air/fuel ratios over the total range of speeds and loads and a flat air/fuel ratio characteristic at wide open throttle.

Now, do you have any easy questions?

[Andereck]

First off, thank you very much for the explanation. Not only did you explain how it worked but you actually gave me enough info to think about what a change there can do, if warranted. This information is now finally in print! I have stacks of books, but not one of them goes into detail about the subject.

Ok, an easy question.

There is something about my tuning that causes all of the combinations I've had to come down from rpm like I have a 50# flywheel. If I tap the throttle the rpm jumps up but the trip back down takes awhile. I'm pretty concious about the throttle plate/transfer slot relationship. The primary throttles are usually a square with the secondary side exposing just a sliver of the slot. I have drilled many a throttle plate to maintain this relationship on my own stuff. I say this because I thought that transfer slot fuel might have something to do with this admittedly non-issue.

The engines have all had some compression. From a solid 11.0:1 302 Chevy to 14.5+:1 355 Chevy. A bunch of combinations in there.

People that have had roughly the same stuff as me get throttle response that seems as if the engine is locked to the carburetor. One way or another they've had some work done by a carb guru, which clearly I am not. There aren't any stickers out there with my name on them!

I usually run non tube type accellerator pump nozzles. When I first used my LM1 I was able to see the difference in fuel pullover from tube to non-tube. (I also discoverred a missing check needle with it). I can't help but think that the response I'm looking for is lurking in something simple?

Regardless of whether you choose to opine on this one, thank you very much for your insiight. I would be happy to send you a book from Amazon or something for your assistance with the emulsion system explanation. I have been searching for info on that for a long time.

[Tuner]

What you read there is a compilation of what you would find in SAE papers, college textbooks like Obert (Univ. of Wisconsin) and Taylor (MIT) and gettin’ bucked off at more than a few rodeos. Obert gives it a couple of paragraphs and a chart that sum it up in general but there are no specifics. There is good math in both sources. I tried plundering the “e-holes” in the `60’s when I had read a Webber book and thought it looked simple. I had even tuned a few Webbers and Solexes and played around with the emulsion tubes with some success. They responded like the book said they would so it looked pretty easy. They didn’t bother to mention the obvious and I was too blind with success to see that the large diameter “e-holes” were used in carburetors whose barrels were only feeding one cylinder. That was about when I learned that changing the little air holes in a Holley would make people frown and soil their spark plugs with soot. But the book said bigger air holes would make it leaner?? Oops! The old time Holley engineers could have made the “e-holes” any size they wanted but they are all, with no exceptions I am aware of, .026” or .028” in production carbs of the `50’s and `60’s and they all ran good. As the years have passed I have come to learn that what size the hole measures depends on what the temperature of the part is when you measure it and what it was when it was drilled.

Why don’t you de-claw (or exorcize) one of your units by converting it as close as you can to the `60’s 780 Holley recipe for the air bleed system and fine tuning it like 471_magnum is doing? As far as I know at this point his carb is right side up on the main well air bleed issue. Do you have and old carb to copy? Plug the redundant holes and jet down the others with 6-32 set screws. I have seen an 850 mightily in need of an exorcism on a 500 inch BBC that was lean enough at WOT to round the plug electrodes with no jets in the secondaries. No kidding!

Your lazy return to idle must be because as it slows down it is passing through a range of AFR’s such that it wants to be at the AFR it is coming from (at the higher speed) rather than the one it is going to (at the lower speed). A carburetor that has ESHAS (emulsion system hyperactivity syndrome) on a radical engine that needs a lot of air to idle will feed from the main at idle or dropping to idle on a closed throttle. Look to see if that is your case. Standing on flat ground, when the throttle is closed at any engine speed fuel flow from the main should cease.

What have you got going on with your distributor? A lot of carburetor problems are ignition timing related. For example, too much spark advance is often “fixed” by leaning the mixture. The leaner mixture burns slower and the peak pressure is adjusted to the sweet spot. A sticky advance mechanism that doesn’t retard correctly will hang at a fast idle until it finally retards

Can you log some data and post it? If you have some in the forum already, put a link in your next post. This could get interesting.

[Tuner]

Hi Charlie,
Thanks for the complement, but I want all you guys reading my comments to remember that these are just my opinions. You should form your own conclusions after you think things over in the context of your own circumstances. Because I can’t be there to see and hear and smell what is going on the consequences have to be in your hands.

Originally Posted by charlie1

i've just finished watching highlights from 2005 Super Stock Hemi challenge and had already noted the "cloud of black soot" when these cars launch. Can you elaborate on the reasoning's why they run such a rich mixture.

Have you read the Mopar manifold modifications and jetting instructions for those engines? If you have, the glimpse of what is done to get even fuel distribution should explain a lot of your question. You have to put enough fuel in the manifold to run the leanest cylinder without misfiring. Some times the only compromise ends up with a cylinder so rich it is sooty but the engine is more powerful than if one misfired completely. Accelerating is most difficult because liquid fuel is 650 times heavier than air and it can’t get to the runner entrances as quickly and easily. The only solution is to over fuel momentarily and live with the wasted fuel to avoid a misfire.

A lot of race fuels (most) have high percentages of the aromatics, benzene, toluene and xylene. These hydrocarbons have sootier burning characteristics than the alkylates that make up most other high-octane hydrocarbons. A little over richness gets sooty fast when high aromatic content fuel is used. That, and the tendency to soften rubber parts is why aromatics are forbidden in av-gas. Supercharged aircraft may run richer than 10/1 for engine cooling on take off and the soot cannot be tolerated.

Can you watch the Hemi challenge again? I’ll bet that all the cars don’t do the soot thing. If some of them have a traction control like the acceleration rate sensitive MSD box there is going to be smoke because they are misfiring on purpose. In `Vegas last month at the Mopars At The Strip I saw some cars that left soft and then got up on it a few feet or a couple of car lengths out. I thought they had some kind of traction device but I was told the class doesn’t allow them. Of course, nobody would cheat. On a closer look, the cars that ran the best numbers had the original `60’s stuff and they left like a rocket. The two-steppers had the “new-same as” carbs. I don’t know what state of tune any of them were in. One guy had his carbs on backwards and didn’t even want to hear about it. The fact that each venturi has a different size jet for a reason didn’t matter, he liked how it looked.

As coincidence would have it, today’s journey to the track included a conversation with a guy who has a Race Hemi with a pair of the “new-same as original” carbs. His experience with them is similar to what I saw in `Vegas a few weeks ago. I have repaired a couple of sets of the new carbs and have worked on the originals occasionally since they were original. The new carbs (at least the ones I have examined close enough to measure the calibration) are not the same as the old ones in the idle circuit. Because they won’t idle at the correct throttle position, the butterflies get opened farther to get what idle there is and they end up running with the main discharging. The big ol’ empty manifold gets full of puddles of liquid fuel and then the mixture is too rich in a sort of random glob now and then sort of way. Mr. Hemi driver sees the black plugs and experiences the loading up on the return road and does what people do when an engine runs too rich, he puts in smaller jets. Ironically, these things will still load up with jets 10 sizes smaller than Mopar recommends in the carb advice, but they don’t run very good down the track.

As further coincidence would have it, he has a brand new LM-1 and LMA-3 combo that he will install in the next few days and we discussed meeting at the neighborhood dyno for a little tuning party.

[charlie1]

Tuner
Yeh a few years ago i looked at the factory tuning for the street hemi carter afb 2x4bbl carbs and how mopar (and the Alan Vanke modified manifolds / carbs)had different jets in either of each secondary or primary of the same carb, so i could see they were trying to achieve an even afr distribution in the cylinders.
Their was quite a difference for example front carb had .089 in one sec and a .1065 for the other secondary.
Just had a quick glance at the mopar race hemi (holley tune)and its clearer how much undertanding and effort they went to obtaining the best tune with staggered restricters/ power valve & jets they used

The hemi ss challenge cars seem to have quite a bit of freedom in intake manifold design and are custom sheet metal jobs with Harry's car having inline carbs vs, the original crossram setup. So i thought the "freedom" in design would have contributed to a close to ideal afr distribution, rather than overfueling on some cylinders.
But in saying that im not sure of the intake carb layout/design of the "sooty" car(s)

I'll havent had time to have another viewing of the dvd but yes it was only a couple of cars which were noticable, and if i remember rightly one was the in the top et cars.
Its interesting the "same as original" carbs aren't quite that at all, and in watching a big dollar class with many controlled engine restrictions of how different the engine sounds / response (tunes) there were.
Cheers

[Andereck]

Hello, I'm sorry I haven't replied sooner to your advice. I havn't an opportunity yet to experiment. I don't have logs on the combinations I complained about. The only logs I have on a fast combination is a nitrous engine that I had running so fat on the bottle that it bottomed out the WB sensor and errored out, and I thought it was running great with no plug color! The LM1 needs to ship with a coupon for 40 spline axles. I'm serious.

Anyways I have the 9th edition of Mopar Engines if anybody is looking for information out of it. I'm not even a Mopar guy, but I had to see how the other side lived a while back. One thing I can comment on is that the Hemi S/S racer is not going to be told anything. They have to find out for themselves, when nobody is looking. I've been around a few of them professionally, some big boys too, and with a couple of pleasant exceptions most aren't getting holiday greeting cards. I do know there is measurable power in power valves on a crossram engine. (crossram being a loose term these days, more like plain old sheetmetal tunnel ram with an offset).

I'll work on providing some real information to chew on via data logs as soon as I can screw one of my projects back together.

[TooMuchHemi]

I'm fascinated by the mention of these old Mopar or old hemi books, and the info they contain about what changes the engineers (or whomever) made. Can you give me some titles or other info, so I can start to look for them. It may be a fruitless search, but I found a hen's tooth last month, so..............

Thanks!

[Tuner]

The hen and her teeth are available at the Mopar dealer. The Mopar Performance web site has a list of publications available from them. All the engines used to be in one big book P5249704 is the 9th edition. Now I see the each engine gets it's own seperate book. Each book is probably just a chapter of the old big one. When I was in `Vegas I borrowed a B/RB version from a vendor to help a guy with a Max Wedge that was trying to make it run with a pair of Edelbrock 750's. We only looked close at the carb section but it looked the same as the B/RB chapter in the book I have.

[Andereck]

I'll tell you what TooMuchHemi, I'll send this book to you to read, photocopy or whatever. Just send it back someday. It's not pretty, the cover has been wet but the pages are fine. It rattled around in the back of my old Monte Carlo for a while but the potatoes are still there. Its 850 pages of gospel from the engineering department.

If you want it email me at [edited] and send your address.

[slcalddrag]

I found a holley 855 on ebay L- 3418 the air horn been cut off it .is it worth anything? Saw Tuner talking about this carb in another thread.

[type26owner]

Since the mystery of the E-holes is solved in that they are actually a passive type of accelerator pump due to the air bubble pumping effect now I'd like to clear another misconception. The top most hole is commonly called an anti-siphon device. That is impossible for it serve that purpose if you understand the physics of a siphon. What that hole does do is control the start of fuel flow from the mains by controlling the vacuum signal.

[shrinker]

Hello type 26 owner; I dont know if it should be said that the e-holes are passive accelerator pumps. I have thought about your analogy of this and I think that if the air bubble is pumping fuel as you suggest then that would actually be the undesirable condition of pulsed flow Klaus and Tuner have mentioned in other threads. I think the objective is to maintain liquid and gas flow in side by side or coexisting flow configuration not in bubbles or slugs. If you reference the patents of the DamBest carburetor there is good explanations of flow there. I have done similar tests to the weber videos myself and found that it slugs if the e-tube is not correct diameter. I know that when the fuel exits the booster without enough air the atomization is poor and the engine looses power so I dont think its a good way to go.
Even if you view the e-holes as the overenrichment correction design for the booster I fail to draw a comparison to an accelerator pump. The function of the e-hole correction in this area is to lean off a booster placement that wants to get richer because of the velocity distribution profile of the venturi. Some small engine carburetors offset the booster to the side of the venturi so as to reduce the correction that would be necessary with a central placement. This offsetting enables elimination of the e-hole circuit altogether for some applications. Maybe you are refering to the accelerator analogy as a backwards accelerator ie. one that supplies fuel at high speed but not at low?

[type26owner]

Hi Shrinker,
There are two conditions were enrichment is required to ensure a smooth acceleration. The obvious is when opening the throttles the accelerator pump adds that extra shot of fuel. However, the not so obvious is when the throttles are held motionless and the load reduces on the engine such as cresting a hill then a passive type of mixture enrichment device is required for the engine to accelerate smoothly. Just go do the experiment by opening up the top E-hole and plug off the lower ones and see what happens.

[type26owner]

Shrinker,
The amount of fuel volume that the air bubble pumping effect is likely to contribute is small. Guessing only a few cc's at most. One must now be able to judge what that volume has in relation to the normal consumption rate of a V-8 for instance to understand and appreciate it's likely impact. The rather silly air/fuel ratio can be converted into one of volumes by doing a crude knumbnail calculation. The density difference of fuel to air is about 560 to 1. If the AFR ratio of 13:1 is multipled by 560 then the volume of air to the volume of fuel can be compared. The new volumetric ratio works out to be 7280 to 1 of air to fuel. So for a 7 liter V-8 for every combustion cycle of all eight cylinders at full song that consumes just 1cc of fuel. Adding in only 2cc of fuel at most is going to add fuel to influence the combustion of sixteen cylinders. That happens in a split second.