Ultra XP850 Almost there!
- Thread starter Ironmike
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I read through some of that. That reminded me of what it looks like with too much emulsion.
If you are logging AFR and you see saw tooth lines you almost always have too much emulsion and you are seeing what is called slugging.
You get a slug of fuel and then a slug of air and it keeps alternating.
There is so much air being introduced to the main well that the bubbles start to coalesce into bigger and bigger bubbles and you get that big slug of air.
I always forget to mention this because I don’t think about it until I’m putting a carb together but I think it’s pretty important so I just do it.
That is I always make the size of the main well a straight diameter. As it is, they are tapered and the main well is smaller at the main jet.
Somehow this affects what the air does as it’s introduced to the main well. I always thought the taper was there because it had a function, but I learned the main well is tapered because it’s the only way they can get the metering block off the mold.
What’s funny (funny as in strange) is that even “billet” metering blocks have tapered main wells.
That tells me that they aren’t really billet but castings that are fully machined.
Either way, I take the taper out of the main well when I build or modify a carb.
TT5.9mag
Two atmospheres are better than one
Ding ding ding
Classic Tuner right there lol.
We need to do just like he says and consider pressure differential because that’s what moves fuel through the booster.
TT5.9mag
Two atmospheres are better than one
I spent some hours last night on the dyno testing booster startup point in rpms vs main air bleed size. I tested at no load, high 40's and mid 60's ftlbs torque. My results were that booster startup occurred within 100 rpm regardless of main air bleed size. I tested with .025, .035 and .045 bleeds. I even took the bleed out and it was still within that 100 rpm. My test could be flawed. If it is someone please point out my error. Also maybe someone could try to repeat this test on their motor and report back with their results. I'm starting to think that the main air bleed isn't the cork in the bottle when it comes to booster startup. I attached a photo of my results. please excuse the sloppy writing.
This is a repost of the test I did.
ValiantRacing
Well-Known Member
Can you explain in little more detail what main well taper is and how to get rid of it.
Thanks
When they cast the metering blocks the main well is smaller at the main jet than it is at the top.
They do that to get the metering block out of the mold. I forgot how much smaller it is at the bottom but it’s quite a bit.
IIRC I drill the main well out to .188 but I don’t have my notes in front of me.
I have to assume and maybe I’ll call Tuner tonight and ask him about it but my assumption is the fuel at the bottom of the well will weigh less than in the middle or the top for the same height of fuel.
In other words if we measure the main well in .100 increments the .100 at the bottom will weigh less than the .100 in the middle or the .100 at the top of the main well.
Since the emulsion holes are evenly spaced it’s my opinion (I’m probably wrong which is why I need to talk to Tuner) that since the weight and really even the volume of the fuel at different heights of the main well will be affected differently.
If the main well is the same diameter from top to bottom (no taper) then the fuel will be the same weight (and volume) for the entire length of the main well.
Or I’m just talking and thinking out of my hat.
Thinking about it, this may be covered in NACA Report 49. I have it printed at home and on my iPad but not on my phone.
I’ll call Tuner later tonight.
Edit: I drill the main well. I have thought about drilling and then finishing it with a reamer so it’s round, but that may be picking the fly poop out of the pepper.
TT5.9mag
Two atmospheres are better than one
At the top of the metering blocks there are passages blocked by frost (type) plugs. The main well can be accessed by removing the two inner plugs.
"A larger MAB will start the mains SOONER"
"A smaller MAB will DELAY the start of the mains"
I have seen this posted by some and I have seen the opposite posted by others. Both sides quote books written by experts.
I thought it could be tested and I would know first hand which side was right. The test I did initially was with no load on the engine and changing the main air bleed size and observing at what rpm the mains start flowing fuel. The results I saw were that the mains start flowing at the same rpm regardless of main air bleed size. (This test could be done by anyone with a carburetor that has adjustable main air bleeds, an assortment of bleeds and a tachometer to measure rpm. I would everyone to not take my word for the test that I did and try it themselves. Maybe you will have different results.)
After seeing no change with no load I thought, "maybe it will behave differently with a load on it." Luckily the motor was on the dyno so I could put a measured load on it and observe the rpm that the mains start flowing fuel. I tried it at two different loads. What I estimated as the lower and upper end of the load that would be associated with cruising at highway speed ish. Having a load on the engine resulted in a change at what rpm the mains started flowing fuel but when the main air bleeds were changed the rpm that the mains started flowing at with that load remained the same.
Why? I don't know. It is even possible that test I did ( while remaining consistent with the results) is somehow flawed.
Is there anyone else out there willing to try this test? Even the test without the load?
"A smaller MAB will DELAY the start of the mains"
I have seen this posted by some and I have seen the opposite posted by others. Both sides quote books written by experts.
I thought it could be tested and I would know first hand which side was right. The test I did initially was with no load on the engine and changing the main air bleed size and observing at what rpm the mains start flowing fuel. The results I saw were that the mains start flowing at the same rpm regardless of main air bleed size. (This test could be done by anyone with a carburetor that has adjustable main air bleeds, an assortment of bleeds and a tachometer to measure rpm. I would everyone to not take my word for the test that I did and try it themselves. Maybe you will have different results.)
After seeing no change with no load I thought, "maybe it will behave differently with a load on it." Luckily the motor was on the dyno so I could put a measured load on it and observe the rpm that the mains start flowing fuel. I tried it at two different loads. What I estimated as the lower and upper end of the load that would be associated with cruising at highway speed ish. Having a load on the engine resulted in a change at what rpm the mains started flowing fuel but when the main air bleeds were changed the rpm that the mains started flowing at with that load remained the same.
Why? I don't know. It is even possible that test I did ( while remaining consistent with the results) is somehow flawed.
Is there anyone else out there willing to try this test? Even the test without the load?
I’m not sure you can do the test on an inertia dyno.
I’ll ask Tuner tonight when I call him.
I’ll also ask him about what happens when there is more emulsion than needed and if it affects when the booster starts.
It was tested on an engine dyno with a water brake. I was hoping you would say you will test it on your dyno. Or even on your car without a load.
I have tested it on my dyno.
If you want I’ll do it again on the next engine up. I’m not sure which one it will be but there are at least 5 in line plus a 390 inch deal I’m doing for my friend and mine.
Mine will be last because I’m going to spend the most time with it.
TT5.9mag
Two atmospheres are better than one
I think it’s a combination of vaiables, carb size, engine size, hp requirements as well as emulsion. I hope you report back with his thoughts.
I’m fixing to grab the phone in about 5 minutes.
How did changes in main air bleed affect start of booster flow rpm? Did you check it with a load and if so how much? I would do it again but...
TT5.9mag
Two atmospheres are better than one
And………….
Long talk last night. We covered a ton of ground.
When I get home from the hospital tonight I’ll type it out.
I was told I use too many double negatives, which is true and the reason 92b is having trouble getting the same results as I do is I’m explaining it wrong.
I’ll fix that tonight.
Ironmike
Well-Known Member
Update! if you've been following, I was a little rich at cruise speeds 40 to 60 MPH. Had 34 MAB's all four corners. Mr Turk had a coniption, saying they're way too big. This goes AGAINST what Holley tells you in all the manuals, books, etc.
He suggested going to 26's and 30 at MOST. Again, exactly the opposite of what my book says.
So I tried his advice. Beautiful day today so I took a little ride with the 34 MAB's still in there. Nice level roads cruising at 45 to 60 my gauge shows 13ish to 1. so just for the hell of it i did what Holley says to lean it down and installed 37's. Wow. 11.6 to 12.5 to 1 on the same roads.
So now I follow Newbomb advice and go smaller, down to 30's all 4 corners. 13.5 to 13.8. Again same roads. Holy sh$% I think he's Right again!
My plan now is to just stick in the 26's and it will probably be exactly where I want, since I picked up half a point going from 34's to 30's.
Have done nothing with emulsions.......yet.
So Newbomb..........you were right again. I'm eating crow for dinner.
He suggested going to 26's and 30 at MOST. Again, exactly the opposite of what my book says.
So I tried his advice. Beautiful day today so I took a little ride with the 34 MAB's still in there. Nice level roads cruising at 45 to 60 my gauge shows 13ish to 1. so just for the hell of it i did what Holley says to lean it down and installed 37's. Wow. 11.6 to 12.5 to 1 on the same roads.
So now I follow Newbomb advice and go smaller, down to 30's all 4 corners. 13.5 to 13.8. Again same roads. Holy sh$% I think he's Right again!
My plan now is to just stick in the 26's and it will probably be exactly where I want, since I picked up half a point going from 34's to 30's.
Have done nothing with emulsions.......yet.
So Newbomb..........you were right again. I'm eating crow for dinner.
No need to eat crow. You did the best thing, and that was test what you were being told. Even if the results had been different you’d still get a gold star for doing the work and posting the results.
Obviously I would have wanted to know why the results were different than what I thought they would be, but you did the testing.
Most guys don’t do that.
On top of being counterintuitive, you have to overcome the inertia of reading books by highly regarded authors who certainly have more gravitas that I ever will have.
They are recognized experts in the field and I’m just an internet blowhard who usually doesn’t give an inch of ground.
So kudos to you for doing the work!
Maybe your results will spur others on to do what you are doing and we can take some of the inertia away from the holleyitius machine.
I suggest that when you get the MAB situation settled, get the main jetting back to where it should be, get your power valve timed correctly and then get your emulsion under control I think you will find the Holley carb, when correctly calibrated for the application will make more power than any other carb out there, get as good as fuel mileage as other carbs, maybe better and it will carburate like EFI.
It takes some work but in the end the effort will pay off bigly.
OUTSTANDING JOB!
Ironmike
Well-Known Member
I did. Seems a wee bit lean, but not bad. 3rd gear approaching shift light 13 to 1. Like to get that 12.7 or so..
Think the side without the O2 sensor(drivers side), is probably a bit leaner. According to my plugs.
Ironmike
Well-Known Member
Well thanks for the help. Don't go anywhere, I ain't done yet!
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