Pre-emulsion bleed formulas

[JOHNDOE333]

Hello all,

I am curious if anyone has any formulas or knowledge pertaining to pre-emulsion bleed selection on Holley 4150 and 4500 HP series carbs. I am attempting to develope a starting point based on carb size, displacement, rpm range, and general application. Then my plan is to fine tune it from there. This is for a billet metering block that does not have emulsion tubes in the main wells, instead they have replaceable jets or drilled set screws (6-32 I think). These metering blocks have five (on average) bleeds per barrel and based on what I have seen I am noticing a trend to use the top, middle, and bottom bleeds and block the 2nd and 4th. I have also noticed an average bleed orfice size of .028 I realize that high speed inboard air bleed selection will effect this as well since the pre-emulsion bleeds are down stream of it. Any help or advice is greatly appreciated.

Good day,

 

[JOHNDOE333]

I would like to add a comment to make my question a little more clear. All the air for the main circuit pre-emulsion must first travel through a main air bleed (one per barrel) on top of the carb and is then forced to travel through one or all of the pre-emulsion bleeds depending on how you have them set (blocked completely or open with a certain orfice size). As I stated before this can be up to 5 possible positions which become uncovered in the main well as more and more fuel is required since the positions are vertical and inline with the well. It is the same principal as an emulsion tube but with more tuneability. Thank you for your time.

Good day,

 

[cheapcharlie]

I suspect the placement of these elmusion bleeds would depend on the mounting of the carb(s)cross or front to rear,type of racing, drag oval or road .
as usual I could be and probably am wrong.
I would also like to see opinions on this.

 

[JOHNDOE333]

Thanks for your response Charlie. You bring up an interesting point. Have any thoughts on calculating orfice size?

Good Day,

 

[patprimmer]

My experience is that setting orifice size and position for emulsion tubes is more an art than a science.

I have an old book on tuning Webber carbies that covers the subject.

I will try to find it.

From memory, as the air and fuel are flowing at low speed, the air only enters the emulsion tube through the holes high up, but as speed increases, the air travels further down the well.

If the top holes are to big, to much air enters the tubes at the top at high speed and does not mix well thus giving poor fuel delivery quality, if they are to small, not enough enters at low speed, giving poor fuel delivery quality.

Also, the bigger the air leak into the emulsion tube via the air correction jet and the emulsion tube holes, the leaner the mixture as the pressure drop across the main jet is reduced and there is more air introduced to the metered fuel.

Regards

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[cheapcharlie]

as pat pointed out tuning will be more trial and error than formulas.when you bring air (which is compressable) into the sys fuel flow calculations get real fuzzy.the carb i use has .028 high speed bleed in all 4 locations and all 8 emulsion bleeds are also .028. this is a square bore with 1.687 bores and 1.375 venturis.jetting varys from 78s to 82s.hope this helps get you in the ballpark.

 

[JOHNDOE333]

thanks very much for the helpful responses.

 

[Zapster]

I know little about Holley carbs; however, I am curious what emulsions there is/are in a fuel circuit. By definition an emulsion is “any colloidal suspension of a liquid in another liquid.” Is the term “emulsion bleeds” a way to say atomization circuit bleeds in Holley nomenclature?

 

[JOHNDOE333]

Zapster,

In the Holley, the fuel is pre-emulsified with a small amount of air before going through its final emulsification at the booster. As Pat stated previously as more fuel is required the bowl and main well fuel level drops uncovering more holes in the emulsion tube or equivalent. I have never seen the diameter of these holes vary at all from one to the next and even the main air bleed/corrector seems to be very close in size as well. I am curious to see what Pat can find in that book of his.

Good day,

 

[JOHNDOE333]

Sorry Zapster I didn't answer your question... I believe you are correct in saying that Holley uses emulsion bleed as a atomization term. It is interesting that the definition you have states a liquid to another liquid.

Good Day,

 

[patprimmer]

Strictly speaking the word emulsion implies liquid in liquid which makes fuel/air emulsion a misnomer.

I always presumed different part numbers for Holley metering blocks indicated different atomisation circuits as there seems to be more part numbers than required to explain other variations like carb family type, with or without power valve, with or without idle bleed screws, with or without accelerator pump port.



Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.