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itb balancing method question

General engine tech -- Drag Racing to Circle Track

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Geoff2
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Re: itb balancing method question

Post by Geoff2 » Sun Mar 01, 2020 2:41 am

I disagree with the comment to balance carbs at ~2-3k rpm. You want them synchronised/balanced at idle so that at small, off idle throttle openings where you would be cruising, airflow is even to prevent surging. At 3000 rpm, the difference in airflow because of the greater throttle opening will be a much lower percentage than it is at idle/off idle & would expect no negative impact.

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Re: itb balancing method question

Post by Belgian1979 » Sun Mar 01, 2020 3:09 am

digger wrote:
Sat Feb 29, 2020 5:45 pm
Belgian1979 wrote:
Sat Feb 29, 2020 7:43 am
digger wrote:
Sat Feb 29, 2020 4:39 am
how are the DCOE pairs coupled?

the first thing to do is make sure the shafts on adjacent pairs are coaxial with an alignment fixture this minimises the change in relative position with throttle angle
There is one brass axle going through it from one end to the other with ball bearings on each end of them. The blades are attached to that axle.
Not sure what you are saing about being coaxial. The bodies sit on the manifold runner faces. These were machined, so I assume they were setup from the factory.
So its not a DCOE which is usually two seperate shafts and two seperate bodies connected by a coupler that allows rotation phasing? its one thing for the face to be flat but the two shafts that get coupled need to be coaxial which requires the bodies to be correctly positioned when bolted down as there is usually clearnace between the bolt and bolt holes so the bodies can be angled relative to each other which affcets the coupler phasing
Are you sure weber dcoe's have seperate schafts for the bores?
https://www.ebay.com/p/2044114772

I see what you mean about the alignment but how do you measure/verify that the axle between 2 pairs is a straight line?

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Re: itb balancing method question

Post by Belgian1979 » Sun Mar 01, 2020 3:10 am

Geoff2 wrote:
Sun Mar 01, 2020 2:41 am
I disagree with the comment to balance carbs at ~2-3k rpm. You want them synchronised/balanced at idle so that at small, off idle throttle openings where you would be cruising, airflow is even to prevent surging. At 3000 rpm, the difference in airflow because of the greater throttle opening will be a much lower percentage than it is at idle/off idle & would expect no negative impact.
So far the results seem to vary at higher rpm (was lower than 2000 rpm btw) based on the fluid manometer I have on it.

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Re: itb balancing method question

Post by digger » Sun Mar 01, 2020 4:23 am

Belgian1979 wrote:
Sun Mar 01, 2020 3:09 am
digger wrote:
Sat Feb 29, 2020 5:45 pm
Belgian1979 wrote:
Sat Feb 29, 2020 7:43 am


There is one brass axle going through it from one end to the other with ball bearings on each end of them. The blades are attached to that axle.
Not sure what you are saing about being coaxial. The bodies sit on the manifold runner faces. These were machined, so I assume they were setup from the factory.
So its not a DCOE which is usually two seperate shafts and two seperate bodies connected by a coupler that allows rotation phasing? its one thing for the face to be flat but the two shafts that get coupled need to be coaxial which requires the bodies to be correctly positioned when bolted down as there is usually clearnace between the bolt and bolt holes so the bodies can be angled relative to each other which affcets the coupler phasing
Are you sure weber dcoe's have seperate schafts for the bores?
https://www.ebay.com/p/2044114772

I see what you mean about the alignment but how do you measure/verify that the axle between 2 pairs is a straight line?
I mean Each pair has their own shaft not each bore . I got made a precision profiled plate that bolts to the flanges with zero play using shoulder screws. I use that to get the relationship correct before tightening the bodies down. It really helped some of the variability where at idle the shafts were in phase but at 100% again wot stop there was a measurable variance

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Re: itb balancing method question

Post by peejay » Sun Mar 01, 2020 8:47 am

Geoff2 wrote:
Sun Mar 01, 2020 2:41 am
I disagree with the comment to balance carbs at ~2-3k rpm. You want them synchronised/balanced at idle so that at small, off idle throttle openings where you would be cruising, airflow is even to prevent surging. At 3000 rpm, the difference in airflow because of the greater throttle opening will be a much lower percentage than it is at idle/off idle & would expect no negative impact.
You need to do both. First set the linkage so that the carbs are balanced when the throttles are open, then adjust the idle so the idle is even, leaving the linkage alone.

No direct DCOE experience, but Dell'Orto DHLAs have idle air screws on each bore so you can tweak the idle airflow per-barrel. I would think that DCOEs and half-decent throttle bodies would have the same capability.

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Re: itb balancing method question

Post by Belgian1979 » Sun Mar 01, 2020 9:44 am

I played with it today, but it's crazy how one thing affects another. For example I also found that shutting off EGO had an effect. Engine temps also played a role in how for example the middle cyls acts vs the outer ones.

I first tried to set them outright correct with the blades as close as I could get them, then I made the individual bores of a pair equal by adding air through the bypass, then readjusted the linkages so that the pairs were equal again.
When taking it at 2000 rpm, the balance was gone again. #-o

In the end I closed the bypasses again on all bores and brought it up to 2000 rpm and set them there. They were pretty much the same (little difference with 6&8 which I rebalanced). I let the engine come to idle again and opened the bypasses again to get them equal.
Was able to get them within an inch that way.

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Re: itb balancing method question

Post by ptuomov » Mon Mar 02, 2020 8:11 am

Is there a plenum resonance from the air box? This is crossplane v8.

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Re: itb balancing method question

Post by Belgian1979 » Mon Mar 02, 2020 9:35 am

During balancing the airboxes are off to access the idle and other linkage bolts.

They seem to create waves when on and at anything over 12%TPS.

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Re: itb balancing method question

Post by Caprimaniac » Sat Mar 21, 2020 4:56 pm

Did you "finnish" this tuning- Project and come to a conclusion on what way to Balance the throttles to give the best overall result?

Hopefully I'm in for it in a week. Been doing vacuum lines for the brakes to soften up my racey street-banger.
How to turn GURU in an instant.....

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Re: itb balancing method question

Post by Belgian1979 » Sat Mar 21, 2020 5:31 pm

I got to what is the best setting. Still have to test it out on the street, but we're grounded due to corona right now.

I first balanced it with the flow meter and then with the fluid manometer at idle. This didn't give the best results at higher rpm. I finally set it at 2000 rpm with the flow meter and the
n fine tuned it at idle with the fluid manometer to get it to run as even as possible. Had to do the fluid manometer balance again when I reconnected IAC. The amount of air introduced in that way won't play a huge role at higher rpm due to the amount of air flowing through the blades in that way.

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Re: itb balancing method question

Post by naukkis79 » Sun Mar 22, 2020 5:45 am

Where is your idle stop? For two-row ITB setup you need to put idle stop to linkage, not in throttle bodies. If some throttle body rest to its own idle stop screw all slack in linkage will effect sync.

So I mean that you master idle speed stop would have to be set and place, and all linkage connected and ITB opening relying only on that linkage support when syncing. That's the only way to sync, you cannot have multiple stop screws.

And uniball linkage brings slack, better solution is to use wire from master linkage to axles.

And that master linkage with bush bearing - get rid of it, it will newer work good enough. Simple solution is to just use two adjustable length throttle cables from same rigid position to drive both rows - like all(jap made) motorcycles do.

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Re: itb balancing method question

Post by modok » Sun Mar 22, 2020 2:58 pm

Evidently you know cables, that's good. have a hammer everything looks like a nail. Mechanical linkages can work well also.
Is it designed well, I don't know. Maybe

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Re: itb balancing method question

Post by Belgian1979 » Sun Mar 22, 2020 3:51 pm

modok wrote:
Sun Mar 22, 2020 2:58 pm
Evidently you know cables, that's good. have a hammer everything looks like a nail. Mechanical linkages can work well also.
Is it designed well, I don't know. Maybe
The linkage works pretty well. If there would be any play, it would show up on the TP sensor as jitter. There are 2 throttle stops on each bank. I set the one on the master and then the one on the opposite bank until the tp % goes up .1% and then back out a hair. Always worked.

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Re: itb balancing method question

Post by naukkis79 » Sun Mar 22, 2020 5:02 pm

Belgian1979 wrote:
Sun Mar 22, 2020 3:51 pm

The linkage works pretty well. If there would be any play, it would show up on the TP sensor as jitter. There are 2 throttle stops on each bank. I set the one on the master and then the one on the opposite bank until the tp % goes up .1% and then back out a hair. Always worked.
It just don't work like that. If you want to get your blades in sync you have to use only one idle stop and preload linkage to open other blades, or all blades if idle stop is in linkage. That center-bearing cross link can't be accurate, you want both linkages(or better wires) to left from same place as there will be some distortion and that distortion will effect sync if not designed to cope with it.

But good luck with your setup, I will guarantee that you will have sync problems until you make throttle linkage that works.

There's zero point to use time and accurate sync tools if there is any slack in opening mechanism - and making rigid enough linkage for two banks isn't easy job at all.

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Re: itb balancing method question

Post by Geoff2 » Mon Mar 23, 2020 5:17 am

Naukkis,
You are exactly right. You need to have one central throttle stop. Both or idle & WOT position. Otherwise expect synchronisation problems...

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