Balance tube with DCOE carbies?

[Turdinator]

I am in the process of upgrading from DCOE40s to DCOE45s on my 3/2TG hybrid. I have two manifolds to choose from. The first is a standard 2TG manifold ported to take the DCOE45s. The other is what i was running with my DCOE40s. This has been modified to include a balance tube. How important is it to have a balance tube whilst using Webers? If it makes a worth while difference i'll get my modified manifold ported to suit the 45s. Otherwise i'll save my money and use the already ported manifold.

Pictures of the two manifolds.

[styler]

was thinking the same thing just yesterday!

i had a look around on the net and the general idea seems to be that air rushes in when valve opens and then valve shuts causing all the air to compress and sends a sharp pulse of air back through the carby which cocks up the signals through the carby so it doesnt run at an optimal state. so the balance tube allows the a small pulse air to escape rather than go back through the carby. if all runners are connected then the balance tube would always have one of the runners on intake and so have a small vacuum always present to draw out the pulses from the runners with the valve that just closed.

now dont take that in concrete

but thats the general idea i got from reading about it as well as someone posted about balance tubes in a vacuum thread i made, saying 18rgs have one but i checked my 2tg manifold and it has plugged holes in the first and last (two outer) runners which may have been some sort of balance tube but i cant find any pics or tech that 2tg carb version came with balance tube from factory?

also it would be logical that you need all 4 runners connected up with sidedrafts as they have individual venturis as shown in your manifold,

[sillycar chick]

AFAIK you dont need balance tubes IF your carbies are all balanced and tuned individually and are all in sync. In an ideal world, this isnt always the case, especially in this day and age where these carbies are getting older and its more common to find they are in need of a rebuild, and arent responding to tuning properly (or are at least poorly tuned, as not so many people these days know how to tune them). This COULD be why you may want to use a balance line system, if carbies arent all balanced properly, to help try and balance them out, but im not exactly sure myself.

RAd28 has 45DCOEs on his 18RG, when we got the car the manifold was connected up via 4 vacuum lines. We disconnected the tubes and blocked each hole off and tuned the carbies properly and theyve been running pretty sweet.

Im no expert on any of this, just speaking from recent experiences.

Red circled bits are for balance lines between the manifold runners, these WERE all joined together, and going to a vacuum gauge in cab. we since have balanced the runners so they run perfectly, and have blocked them off.

BUT then you have the way its set up from factory, which looks to be about the same way I have the solexs set up on the hybrid:



2 manifold vaccum lines are balanced up and run down to the vacuum box on the side of the block via a PCV valve....

I would suggest blocking them off first and see how you go with tuning, if not you could try blocking the 2 outer ones, and joining the 2 inner ones and down to the vacuum box via a PCV valve.

[styler]

you sure you not mixing up balancing with the carbies with a balance tube?

as they are seperate things, balancing or synchronizing of the carbies is to run them them in sync, usually done with a sync tool ie stk or unisyn or carbtune or 4 vac gauge sets etc which all read the vacuum.
in short you get the reading the same on each venturi and then they are balanced with each other and run much better.

but the balance tube is when the carbs are running and have sharp back pulses which can be moved through the balance tube rather than travel back through the carbies and affect the carbs running. probably more of a problem at higher rpm when air velocity is higher.

also i have read you are meant to run the balance tube when balancing carbies which makes sense, otherwise if you connect it afterwards its going to change the readings slightly.

thats as far as i got into it all...

[sillycar chick]

Nah im not getting mixed up just having a really bad day with words and having trouble explaining shit right now I know the difference between using vac guauges on each point to balance and tune carbies and the "balance" line used between the carbies from factory. But I have heard of people using a "balance" line between carbies to keep them more in sync, but its kinda the cheats way to balancing carbies. If the carbs are balanced and tuned properly you wouldnt need any balance lines between them for the purpose of syncronisation.

We tuned RAd's carbies with 1 guauge on each seperate connection on the manifold as there were 4 connections. With my solexs on the hybrid however, i only have 2 connections on the manifold, so clearly we could only balance and tune the carbies using 2 vac guauges. I have that balance pipe between the two inner vac lines off the manifold on mine, and Styler I think this is the diagram you are referring to that you couldnt find. It shows what I have.



Your theory was pretty interesting, ive never come across that before. But Rad's carbies are running fine, if not very well, given that we have blocked off each runner and arent using a balance pipe. His dad, a mechanic with a background of working in racing teams and experience in tuning these carbies, advised just to block each connection on the manifold up and get rid of the hoses that were on there. I cant exactly remember how the PCV valve is setup on his engine, but its not running off the carbies. AFAIK the "balance" tube is there as part of the ventilation system in the engine. But im not completely dismissing your theory either, I just dont have any experience on it so cant really comment (and no offence, but you said you found it on the net, so we dont even know how relevant it is to this particular application either ).

When I get a chance i'll ask rad's dad about it, and see if I can find some reference material somewhere that explains exactly why that balance pipe was put on these engines from factory.

In the meantime Marcus, i'd say save your dosh and go with the ported manifold, because I dont think its going to matter once your carbies are properly tuned whether you have 2 or 4 connections.

[Screamn_Sleeka]

With out fighting anyone’s theories, Ferrari and Maserati never used balance pipes with their weber'ed cars (ie all their cars before efi).

[RAd28]

acctually i'm intrigued by stylers theory... 'cause it does make sense to a point, however i can't imagine it working as well as it would in theory... simply because you've got a 5-6mm orifice to remove a very fast moving pulse from a 40-45mm throat... more so, i would expect this to be LESS useful as engine RPM increase due to the high air speed maintaining momentum, meaning the reversion pulse would have a lesser effect and travel less distance (possibly part of the reason why short runners = good high RPM speed).

honestly i have nothing other then theories to bring to the arguement either, no first hand experience... but it might be worth experimenting...

[Rodger]

The balance tubes used on both the 2T-G and 18R-G are on there simply to, evenly distribute the gasses drawn from the PCV system and all the rest of the plumbing extending from them relates to all the effort of Toyota to meet anti-polution requirements of the period.

All may have noticed that the spacer blocks on both the 2T-G and 18R-G manifolds have slots to provide connection between each branch of the balance tube and each pair of carby barrels.

Care needs to be taken when replacing the spacer blocks with softmounts, as any balance tube system and its connected PCV/polution plumbing needs to be blocked or re-routed as there would no longer be any passage into the engines inlet tract to suck in the fumes or provide vacuum signals/references.

Vacuum for the dissy vac advance is seperate and is almost always drawn from the front barrel of the front carby (just before the Pilot System outlet) only.

All my motors that have run the Solex/Mikuni have not had balance tubes as such, however I have plumbed in the PCV system from time to time using the 2T Mikuni manifold ports. However all my set ups use the OEM spacer blocks with the slots connecting the two barrels. Whether they actually perform any function like this I cannot determine as I have no problems with tuning.

Regards

Rodger

[1jzracing]

bigest MYTH ever to put balance tubes on webbers!! they should NEVER have one

they are designed to run ONE cylender each and will be imposable to tune or get the idle mixtures right if one carb is feeding air from another one

multi t/b EFI however must use one to get the mixture perfect as the fuel delivery is even across all the injectors so the air pressure benifits from an equilisation tube,

PS bet money it goes better with the 40's that it ever will with the 45's

[Turdinator]

bigest MYTH ever to put balance tubes on webbers!! they should NEVER have one

Good to hear. I've decided to go with the manifold without the tube.

PS bet money it goes better with the 40's that it ever will with the 45's

Interesting. I'm running 36mm chokes at the moment and from what i've read this is too big to run in 40s. That the 40s are restricting airflow. There is a chart mapping flow of 40 and 45dcoes relative to choke size i've seen in many weber tuning books to back this up. I'll see if i can find it online somewhere...