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Twin SU manifold design.
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Author:  cazmo [ Sun Nov 19, 2006 4:51 pm ]
Post subject:  Twin SU manifold design.
hey guys.

i've decided to have a go at making my own twin su inlet manifold (aluminium of course). I'm able to make one at work being a sheetmetal apprentice and i also have access to a TIG and plenty of material.

I'm basically after some design advice.

Do the carbs have to have a pipe joining them? I don't plan on running a booster or PCV.

Any other ideas you guys might have would be great.

Cheers, Cameron
Author:  drmini in aust [ Sun Nov 19, 2006 4:55 pm ]
Post subject: 
Yes they do, as they are SUs- a constant depression carb which have a vacuum operated piston.. and the vacuum level in each port goes `high/high/zero/zero' with the induction pulses.

If you try and do it with NO balance pipe, the pistons in the carbs will flutter and the mixture will be all over the place.
I would look at the Maniflow steel one (arguably the best flowing design right now) and put the balance pipe as shown. :wink:
Image
Author:  simon k [ Sun Nov 19, 2006 5:33 pm ]
Post subject: 
there is lots of design advice in Vizard's "tuning BL's A series engine" - including Vizards own design which he reckons was 99% efficient - the VS1 manifold, but I believe it never went into production

got access to a flowbench? ;)
Author:  LS1380 [ Sun Nov 19, 2006 5:49 pm ]
Post subject: 
Pic of Maniflow manifold,which I got posted out from UK.
Shows the equaliser tube.
Image
Author:  cazmo [ Sun Nov 19, 2006 6:02 pm ]
Post subject: 
thanks for the info.

so, a balance pipe is definately needed.

LS1380 - what's the diameter of that balance pipe on the maniflow?

skssgn - unfortunatly no access to a flowbench :(
Author:  Sir Yun [ Mon Nov 20, 2006 7:01 am ]
Post subject: 
you could have a look at the VS1 manifold as well if you want something a bit more challenging.
Author:  Matt68 [ Mon Nov 20, 2006 10:42 am ]
Post subject: 
The maniflow one is done originally in mild steel.

This pic shows mine:
Image

The balance pipe is around 7/16" to 1/2" internal diameter, the bores of the manifold itself are 1 1/4" at the carb face (as I wanted one for twin 1 1/4" carbs, natch :wink: ) and match the port size at the other end (12g940 inlet ports.)

It is curved, not straight, so no easy task I reckon. (tapered curve pipe)

If doing this yourself, make the pipes longer as it will increase torque, but make sure the carb face is still on close to the correct angle. (The doc will know this one) Make sure you won't hit the bulk head!

Good luck!

Matt
Author:  drmini in aust [ Mon Nov 20, 2006 10:53 am ]
Post subject: 
Correct angle for twins on a Mini is 30*. :wink:

I made a 15* steel one years ago for a pair of Amal Monobloc bike carbs on my 1220,
I kept the pipe straight and put the flanges each end at 7.5*.
It worked well, but putting them at 15* each end to get 30* total will be too much, IMO.
Author:  LS1380 [ Mon Nov 20, 2006 4:23 pm ]
Post subject: 
Motorbike Carbs-Is that anything like these?
Image
Author:  drmini in aust [ Mon Nov 20, 2006 7:46 pm ]
Post subject: 
Like this, but a LH and a RH, as used on original Bonneville.
I used the Bonny 2-1 cable link too. :lol:
Image
Author:  kiwiinwgtn [ Tue Nov 21, 2006 7:39 pm ]
Post subject: 
Please post pics when you are done, i am interested in making one also

Cheers kiwiinwgtn
Author:  LS1380 [ Tue Nov 21, 2006 8:42 pm ]
Post subject: 
I found the invoice from when I purchased the manifold from Maniflow.
Purchased in 2004 for 95.00pounds plus postage 15.00pounds.
Total 110.00pounds-so just a thought,could you make one cheaper or better than?
Author:  cazmo [ Tue Nov 21, 2006 9:25 pm ]
Post subject: 
LS1380 - will definately be able to make one cheaper, don't know about better though as i don't have access to a flow bench. I will definately give it a go.
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