32 replies to this topic

[jpw1275]

Hi all.... I've been thinking about this for a bit now being a carb addict etc..... Could you run a twin su set up without having the manifold being joined with a balance tube or whatever they are called.... I'm thinking of making 2 separate manifolds for each carb and wondered if it would work...... Your imput is needed...:0)

Cheers James

[Dusky]

it would. Weber style manifolds dont have the tube. But why dont you vizardise the manifold?

[jpw1275]

I just want to make something bespoke and not the ordinary....;0)

Cheers james

[jpw1275]

I'm also thinking of making it bit longer aswell or would it be better the manifold being shorter than original?

Cheers james

Edited by jpw1275, 09 June 2014 - 07:24 PM.

[Cooperman]

A single unconnected feed to each carb would be a great improvement on the original 'log' manifold. If it could be slightly longer it would improve the inertial ramming into the cylinders and make for better running. However, the carbs would need to be very accurately balanced at setting up and one on the tubes would need the servo vacuum take off stub. Maybe put a vacuum stub on each tube joined with a T-piece.

Interesting project which should work well. Let us know how it goes.

[jpw1275]

I don't run a servo with my brakes so I have no need .....:0)

Cheers james

[jpw1275]

Cheers cooperman I will get onto it.....:0)..... As for setting up I guess the only way to do it is the old fashioned way of listening to the hisss....

Cheers james

[Cooperman]

Or use one of those balancing devices. It should improve the top end throttle response a lot if done properly.

[jpw1275]

Or use one of those balancing devices. It should improve the top end throttle response a lot if done properly.

Ah yes..... I think I have one of those in the garage somewhere.....

My next question is ....... Ally or steel or should there be no real difference or would steel be too smooth?

Cheers

[Cooperman]

Steel will be much easier to weld and cheaper too. You might need to taper the tubes slightly to get the correct diameters at each end, then weld on the square plates, 1/4" thick I would suggest to match the thickness of the exhaust manifold flanges (check this thickness). They must be the same thickness so that the big washers will nip the inlet & ex. manifolds equally at the two middle bolts.

Clean back the welds, clean up the bores and fit the carbs.

Good luck with this.

[jpw1275]

Cheers coops.....

[Dusky]

Interesting! keep me updated :)

[Cooperman]

Cheers cooperman I will get onto it.....:0)..... As for setting up I guess the only way to do it is the old fashioned way of listening to the hisss....

Cheers james

Sounds like you could put these into production and sell them on here.

Almost any inlet manifold for twins is better than the original BMC one.

[carbon]

Interesting thread, just how important is the balance tube between the two ports on a twin carb set-up?

 

The high flowing maniflow steel inlets make do with a pipe about 1/2 inch diameter. Some of the early speedwell conversions I have seen in pictures used an even smaller balance tube. BMC factory seem to have anything from about 1/2 inch ID to 3/4 inch ID...

 

If you get rid of the balance tube altogether does this have other side effects on the carburation for road use?

[Cooperman]

In theory the balance tube should do nothing. In practice it just allows a bit of imbalance correction if the carbs are not perfectly balanced. It would be worth trying without and going for a very accurate balance when doing the initial set up. It would be easy to add a small diameter balance tube, say 3/8" diameter, later if necessary.