32 replies to this topic

[timmy850]

Speedwell made these in the 60's

(Third and fourth down the page)
http://mk1-performan...g_equipment.htm

[miniman24]

As said above, similar ones were made by Speedwell, been looking for a set for a long time!

[Captain Mainwaring]

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.

 

 

Looki at the firing order, the port layout and think about that one again

 

You lose half your potential ram air effect without the balance pipes - it's about catching up on harmonics.

Edited by Captain Mainwaring, 10 June 2014 - 04:19 AM.

[carbon]

The Captain has a point here.

 

Inlets to cylinders 1 & 2 are siamesed, as are 3 & 4. Firing order (ie induction order) is 2,1 then 3,4.

 

Does the balance pipe have a purpose of keeping some gas flowing through both carbs at all times? I seem to recall Vizard spent a lot of time developing a twin SU inlet manifold, and that in this design the balance pipe volume was adjustable to allow this to be optimised.

 

If there is no balance pipe then the gas flow will be much more pulsating, and would this mess up the carburation?

[jpw1275]

Ahwell back to the drawing board......

Cheers james

[Captain Mainwaring]

The Captain has a point here.

 

Inlets to cylinders 1 & 2 are siamesed, as are 3 & 4. Firing order (ie induction order) is 2,1 then 3,4.

 

Does the balance pipe have a purpose of keeping some gas flowing through both carbs at all times? I seem to recall Vizard spent a lot of time developing a twin SU inlet manifold, and that in this design the balance pipe volume was adjustable to allow this to be optimised.

 

If there is no balance pipe then the gas flow will be much more pulsating, and would this mess up the carburation?

 

 

Yes - you want ram air effect on every induction stroke...inlet valve shutting. 1 shutting should cause a pressure wave that helps the induction into 3 , but with no balance pipe it won't happen.

In fact with no balance pipe you'll get some nasty flow reversals at certain revs which will cause the charge to actually "mist" out of the carb mouth - take a look, you can see it.

[OfMini&Men]

Speed well did a manifold that wasn't connected it was just a single track to the Inlet

 

 

http://mk1-performan...g_equipment.htm

 

 

 

This site has information on them

[jpw1275]

Speed well did a manifold that wasn't connected it was just a single track to the Inlet
 
 
http://mk1-performan...g_equipment.htm
 
 
 
This site has information on them

cheers for that..... but the speedwell ones where connected with a rubber tube in a c shape to each manifold to act as a balance tube..... the fact that all manifold for twin su"s have a balance bar makes me think it is needed as previously said in this thread.

i may have to make a manifold with a balance tube but are all the balance tubes a certain diameter or does it not matter?

Id like to make a manifold abit longer than standard and more straight than curved.

cheers james

Edited by jpw1275, 10 June 2014 - 03:23 PM.

[carbon]

The work David Vizard did to develop the VS1 manifold for twin SU carbs is on pages 152-154 of the blue version of 'Tuning BL's A-series Engine'.

 

A very nice design, great pity this is not available...

[jpw1275]

I dont think i have that book but il have alook when im home.... anychance you can put a piccy up of the manifold....:0)

Cheers james

[OfMini&Men]

Have a good at making some out steel first if you can weld or even if your a dab hand with CAD have a go on there

 

I've been thinking how I can cold air flow twin HS2's as Mini's set up annoys me

[petehuws]

This all should work perfectly & stunningly well, this would assume both carbs are perfectly balanced with each other, all a carb does is to deliver a fuel/air mixture for ignition.  I always thought though that the insides of an inlet should be left mottled or rough to aid fuel atomisation, would a shiny, smooth inlet surface affect this?  I've never peered into a Maniflow or similar twin inlet so difficult to know.

[jpw1275]

I think it will be just a case of trying it and seeing.... As for balancing ..... It would be easier to disengage the linkage to make the carbs separate ..... The unfortunate thing is at the moment my car/engine aren't in any stateto be used, so I may have to use another vehicle to try it on like cliffs on here...:0)

Cheers james

[Captain Mainwaring]

 

Speed well did a manifold that wasn't connected it was just a single track to the Inlet
 
 
http://mk1-performan...g_equipment.htm
 
 
 
This site has information on them

cheers for that..... but the speedwell ones where connected with a rubber tube in a c shape to each manifold to act as a balance tube..... the fact that all manifold for twin su"s have a balance bar makes me think it is needed as previously said in this thread.

i may have to make a manifold with a balance tube but are all the balance tubes a certain diameter or does it not matter?

Id like to make a manifold abit longer than standard and more straight than curved.

cheers james

 

 

 

Yes it matters  

think about it - you are trying to attain inlets tracts that are ideally all the same length, and moreover you are looking to attain gas velocities that  create pressure waves that coincide with valve openings to increase torque or power (whichever as is your desire) - if you mess around with the balance pipe length or diameter then you mess around with it's resonance - it's a bit like two stroke exhaust systems.

 

I've just bought a Kawa ZX10 - and the tuned inlet system and ramair adds as much as 20 BHP at 160 MPH.

[timmy850]

What you could do to test it first is get a working twin manifold (preferably on a working car) and block the balance tube. See how well it runs before and after?