Annular boosters on a Tunnel Ram

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My initial thought is I might try and drop the IFR’s first. I always used a larger IFR because of a lean condition in the 50-60mph cruise area with anything smaller than .033 (Just at the end of the transition slot and beginning of the mains). Thinking that the mains are coming in earlier now so dropping the IFR’s may help clean up low speed cruise without hurting the transition area.
 
TT5.9mag said:
Edit; jetting won’t really affect where you were testing. Idle, light throttle and cruise. Where did the extra fuel come from?
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Just spitballing here, is it possible that the increased physical size of the boosters is creating higher air velocity causing it to pull more fuel from the transition slots?
 
After going through my notes, I grabbed the old main bodies and by god if there weren’t .080 transition slot restrictors in the primary side. Didn’t put them in the new bodies. That sure sounds like the cause of the low speed cruise being richer. Doh! @TT5.9mag
 
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MomsDuster said:
After going through my notes, I grabbed the lot main bodies and by god if there weren’t .080 transition slot restrictors in the primary side. Didn’t put them in the new bodies. That sure sounds like the cause of the low speed cruise being richer. Doh! @TT5.9mag
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There ya go!
 
I’ll bite. What’s CRS?


Just realized “can’t remember ****”
I have the same affliction
 
71GSS,
Unfortunately in your post #68, logic is missing from the first three lines.
If a larger MAB starts the mains sooner [ it doesn't ] & flows more fuel, then it follows using the same logic that increasing the MAB will increase the fuel flow even further; not stop it as you say.


Although it was not you who said it, NOWHERE in any any of the links provided in this thread does it say these simple words or words that have the same meaning: a bigger MAB starts the main system sooner. If I missed it can somebody please point it out....

Another point to remember. At some point as the throttle is opened, the idle system tails off in conjunction with the start of the main system to allow for a smooth transition between one system finishing & another starting.
 
Rat Bastid said:
I wouldn’t call that your “interpretation” because you nailed it.

Thats exactly what it says, and that’s exactly how it works.

Its almost absurd watching a simple definition of how the MAB functions get so twisted up that it becomes convoluted.

The main air bleed can (and does) behave exactly as described above because (once again, exactly what it says in the text) the pressure differential across the booster and the MAB are different at different air flows.

Thats why a bigger MAB will START the mains SOONER and still make the fuel curve tilt leaner at higher air flows.

Evidently some can’t grasp the pressure differential at different air flows.

Regardless of all that, it’s really simple to test MAB function. All one needs to do is test it and you’ll find that Tuner’s explanation is exactly how it works.

Of course, I have the luxury of getting the phone and talking to Tuner to make sure I’m understanding what he wrote.

And your explanation is exactly what Tuner says and is exactly what happens in the real world.

I hope this ENDS all this BULLSHIT about MAB functions as it’s exhausting to keep unscrewing the bad information about it.

I have personally posted the GENERAL definition of it by Taylor. Of course, if you want the full explanation you need to get the books and read all of it. And grab a scientific notation calculation and work through the math of it. That makes crystal clear what is happening when you change the MAB.

This is PRECISELY how “holleyitis” happens. Bad information repeated over and over and over bolstered by misquotes, nonsense and repeated error.

This stuff is easily understood if you read what guys like Tuner and Shrinker have written. They have made it very simple.

You just have to shut out the noise and ignore those who say something diametrically opposed to what they are saying.
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Well, I know this. I will continue to follow YOUR carburetor tuning advice, as, so far, it's been DEAD ON THE MONEY and has worked for me.
 
Bewy said:
71GSS,
Unfortunately in your post #68, logic is missing from the first three lines.
If a larger MAB starts the mains sooner [ it doesn't ] & flows more fuel, then it follows using the same logic that increasing the MAB will increase the fuel flow even further; not stop it as you say.


Although it was not you who said it, NOWHERE in any any of the links provided in this thread does it say these simple words or words that have the same meaning: a bigger MAB starts the main system sooner. If I missed it can somebody please point it out....

Another point to remember. At some point as the throttle is opened, the idle system tails off in conjunction with the start of the main system to allow for a smooth transition between one system finishing & another starting.
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I guess my comments and thoughts come from these below. It seems clear to me. From post 58

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.

Here we are discussing main jet and WOT mentioning the larger air bleed, if increased in size, will lessen flow due to pressure difference. This speaks to the MAB being larger, less flow will happen - to the point of no flow if too large. Being the MAB is above the well of fuel.

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".

Bewy, please, I am trying to understand this. If you are reading these statements from Tuner differently, can you please quote the words specifically and explain your understanding?

@MomsDuster Sorry for hijacking your thread with all of this, but I also hope we get some info posted that does help.
 
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71GSSDemon said:
I guess my comments and thoughts come from these below. It seems clear to me. From post 58

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.

Here we are discussing main jet and WOT mentioning the larger air bleed, if increased in size, will lessen flow due to pressure difference. This speaks to the MAB being larger, less flow will happen - to the point of no flow if too large. Being the MAB is above the well of fuel.

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".

Bewy, please, I am trying to understand this. If you are reading these statements from Tuner differently, can you please quote the words specifically and explain your understanding?

@MomsDuster Sorry for hijacking your thread with all of this, but I also hope we get some info posted that does help.
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I offer this as a possible explanation based on my limited knowledge compaired to those who wrote the above quotes. It seems to me that the above quotes are describing fuel flow chariteristics after fuel flow has already been initiated. I believe this because in order for fuel to be emulsified and lighter as described fuel has to be flowing through the main circuit. It could be that the main bleed controls when the circuit is initiated as in larger= later but richer at startup due to decreased weight of a highly emulsified mixture making it feel richer when it comes on. these two things could happen close together in time.
Also there is mention of unpredictable and counter-intuitive results base on air bleed size, emulsion package and booster signal.
 
The reason the main air bleed starts the mains sooner (and that is a result, not necessarily the purpose of the mab) is because at different throttle openings the air moving through the carburetor is not a constant. The pressure drop and the air speed both change at different points in throttle openings and rpm. The extra air introduced into the fuel changes it’s density and that changes it’s flow characteristics.
 
TT5.9mag said:
The reason the main air bleed starts the mains sooner (and that is a result, not necessarily the purpose of the mab) is because at different throttle openings the air moving through the carburetor is not a constant. The pressure drop and the air speed both change at different points in throttle openings and rpm. The extra air introduced into the fuel changes it’s density and that changes it’s flow characteristics.
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THANK YOU.

Just because a bleed (or anything else for that matter) exhibits a certain characteristic at some point, doesn’t mean it will behave the same under different conditions.

Thats why I keep saying over and over you have to understand how pressure differentials affect bleed behavior.

In other words, just because the MAB will tilt the fuel curve lean at high air flows doesn’t mean it has to tilt the fuel curve lean at low air flows.

Which is saying that because the main air bleed tilts the fuel curve lean at HIGH air flows doesn’t mean that it will exhibit that same characteristic at low flows and delay the mains.

Like I also said, this stuff is in the Taylor books, but it also includes the math that makes it makes more sense.

Obert covers it, but not as explicitly.

I think that sometimes the tip in stumble guys run into is more a product of the T slot still providing adequate fuel when the booster starts because the MAB is too large.

Look at an early 3310 Holley. I think (my memory isn’t all that good any more) the MAB is .026 and then look at some of the stuff out there today and you’ll find MAB’s in the .032-.034 range.

And that STARTS the mains SOONER. And that overlap of the T slot providing enough fuel and the mains starting causes a rich tip in stumble.

It is so EASY to get lost in all this stuff because it is counterintuitive at times and because of the misinformation out there.

Tuner and Shrinker have left us a really great amount of knowledge for free if we want to find it and read it.

And Tuner is still around. I’m going to call him later today (he sent me a really cool email that included a 2 part attachment of how GM designs, builds and tests cylinder heads using their flow bench) and tell him once again he NEEDS to write a book.

He thinks no one will read it. I say he is wrong.
 
RustyRatRod said:
Well, I know this. I will continue to follow YOUR carburetor tuning advice, as, so far, it's been DEAD ON THE MONEY and has worked for me.
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I’ve seen his work in person on quite a few cars that are super badass. My car runs like a champ due to his help tuning..
 
Rat Bastid said:
THANK YOU.

Just because a bleed (or anything else for that matter) exhibits a certain characteristic at some point, doesn’t mean it will behave the same under different conditions.

Thats why I keep saying over and over you have to understand how pressure differentials affect bleed behavior.

In other words, just because the MAB will tilt the fuel curve lean at high air flows doesn’t mean it has to tilt the fuel curve lean at low air flows.

Which is saying that because the main air bleed tilts the fuel curve lean at HIGH air flows doesn’t mean that it will exhibit that same characteristic at low flows and delay the mains.

Like I also said, this stuff is in the Taylor books, but it also includes the math that makes it makes more sense.

Obert covers it, but not as explicitly.

I think that sometimes the tip in stumble guys run into is more a product of the T slot still providing adequate fuel when the booster starts because the MAB is too large.

Look at an early 3310 Holley. I think (my memory isn’t all that good any more) the MAB is .026 and then look at some of the stuff out there today and you’ll find MAB’s in the .032-.034 range.

And that STARTS the mains SOONER. And that overlap of the T slot providing enough fuel and the mains starting causes a rich tip in stumble.

It is so EASY to get lost in all this stuff because it is counterintuitive at times and because of the misinformation out there.

Tuner and Shrinker have left us a really great amount of knowledge for free if we want to find it and read it.

And Tuner is still around. I’m going to call him later today (he sent me a really cool email that included a 2 part attachment of how GM designs, builds and tests cylinder heads using their flow bench) and tell him once again he NEEDS to write a book.

He thinks no one will read it. I say he is wrong.
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Please don’t assume I understand all of this. That is wholly untrue. I learned what I know by watching and reading as much as I can by people much smarter than I am (Tuner, Shrinker, and yourself included). I’ve spent a few days on the dyno with Steve Brule at westech and I’ve said it before, when he speaks I LISTEN. There is so much to carburetor tuning that 99% of people will never get in to, AND do the testing that it takes to see the results. I don’t think you’d ever see a MAB act the same on a carb flow bench as it does on an engine. You have test it in both circumstances to see the change. I love the information and I love threads like this. If you have any influence on Tuner writing a book he’s got my vote. Pass that along.
 
The Internal-Combustion in Theory and Practice

Two volumes.

Charles Fayette Taylor.

If you like math you will find these very interesting.

If you love math, you won’t be able to put them down.

If you hate math you’ll probably burn them lol.
 

Rat Bastid said:
The Internal-Combustion in Theory and Practice

Two volumes.

Charles Fayette Taylor.

If you like math you will find these very interesting.

If you love math, you won’t be able to put them down.

If you hate math you’ll probably burn them lol.
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I just ordered a copy of Volume 1. If nothing else, my son will love this book. He is a Junior at Michigan Technological University for Material Science Engineering.
 
Another great book if you are interested in carburetors and carburetion is:

Carburetors & Carburetion by Walter B. Larew

Great book.
 
92b,
Post #86. You get it, go to the top of the class & get your gold star.....
A lot of people on this thread are talking about fuel flow after the main system starts. It has to have a starting point. The straw/liquid example describes the system start up perfectly.
 
T55.9,
Post #87. The MAB starts the main system sooner. Compared to no MAB? Not following.
 
Bewy said:
T55.9,
Post #87. The MAB starts the main system sooner. Compared to no MAB? Not following.
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We’re discussing increasing the size of the MAB and what effect it has on bringing the mains on line. But you knew that. We know you’re not following though, and we know you don’t agree. Cool. Seems a few of us have had different real world experiences and that’s what we’re sharing.
 
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