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twins.....
https://www.ausmini.com/forums/viewtopic.php?f=2&t=32262		 Page 1 of 2
Author:  hothead115 [ Tue May 29, 2007 10:09 pm ]
Post subject:  twins.....
so....my twin 1 3/4 inch su's i finally got running almost perfect on my 1275...little bit of headwork and exhaust and possibly a cam but not sure....everyone on here said she'd run rough....runs perfect, only a tiny cough and splutter at low rpm under load occasionly.
Author:  LS1380 [ Tue May 29, 2007 10:18 pm ]
Post subject: 
Mate..I've been running with twin 1 3/4 and I can't get the smile off my face :D
Author:  Matt68 [ Tue May 29, 2007 10:19 pm ]
Post subject: 
Well I am happy for you!

I still say the low air velocity in your set up means you have less power and torque up to 5000rpm than on my 1310 with twin 1 1/4 carbs (modified of course).

Not saying yours won't run well, it certainly can run well with your carb setup but it will have most benefit at higher rpm levels.

Hence i still say the optimum size for a 1275 is either twin 1.25" or twin 1.5" carbs.

I prefer the 1.25s.... if you have them well set up, and in good condition, they will provide as much fuel and air as the engine can possibly use up to 6000rpm. At a higher velocity, higher VE, therefore more power.

No need for anything else.

At the same time, I really am glad to hear your carbs are working well for you. :D :D

cheers matt
Author:  drmini in aust [ Tue May 29, 2007 10:23 pm ]
Post subject: 
SUs are a constant velocity carby. Even though these ones are thought to be a bit BIG for a Mini, this doesn't mean the airspeed through them is low. They will only lift the pistons as far as the engine needs to. :wink:
Author:  LS1380 [ Tue May 29, 2007 10:28 pm ]
Post subject: 
Orginally i was running with twin 1 1/2,then the difference to 1/34 with good airfilters and set-up on dyno is unbelievable.Also inlet manifold is most important to the set-up.Match ported to head :)
Image
Author:  Matt68 [ Tue May 29, 2007 10:36 pm ]
Post subject: 
drmini in aust wrote:
SUs are a constant velocity carby. Even though these ones are thought to be a bit BIG for a Mini, this doesn't mean the airspeed through them is low. They will only lift the pistons as far as the engine needs to. :wink:


Hi doc,

I thought of that, but was told that it is the shape of the opening under the piston, combined with a larger inlet throat, and a larger outlet port, for the same total volume of air, all mean the velocity is slower on the larger throated SUs.

But as i don't know for sure, will leave it open for the people who do to speak up...

Cheers

Matt
Author:  Matt68 [ Tue May 29, 2007 10:39 pm ]
Post subject: 
LS1380 wrote:
Orginally i was running with twin 1 1/2,then the difference to 1/34 with good airfilters and set-up on dyno is unbelievable.Also inlet manifold is most important to the set-up.Match ported to head :)
Image


I have a maniflow inlet manifold too! Probably the single best improvement you can make for a set of twins!!

Did you notice more power at all levels of the rev range or just better top end? might have been the manifold more than the carbs!! :wink: :wink:

Cheers
Matt
Author:  LS1380 [ Tue May 29, 2007 10:47 pm ]
Post subject: 
Yes you could be right.The manifold took a long time to arrive.
But I think it's all to do with the "whole" set-up-from engine internals to the exhaust system. It revs hard from 2800 until the tacho goes crazy :shock:
Author:  Matt68 [ Tue May 29, 2007 10:56 pm ]
Post subject: 
LS1380 wrote:
Yes you could be right.The manifold took a long time to arrive.
But I think it's all to do with the "whole" set-up-from engine internals to the exhaust system. It revs hard from 2800 until the tacho goes crazy :shock:


I think with most strong engine's it is down to the complete package. I know that swapping to the maniflow manifold made a big difference to mine, but there are a lot of factors which make it a fun car to drive, and make it a strong engine, with Heaps of torque, and mind blowing acceleration (for a mini). It is never just the carbs, or just the head, it is all of them together!!
Author:  mad-mk1 [ Wed May 30, 2007 12:10 am ]
Post subject: 
sorry cooldnt resist

Image

tahts my biam side coming out :twisted:
Author:  mad-mk1 [ Wed May 30, 2007 12:12 am ]
Post subject: 
dammit, oh well, it was teh olsen twins too, i cant be bothered fixing it
Author:  sports850 [ Wed May 30, 2007 10:10 am ]
Post subject: 
Sounds like it worked well but tell me , what's it like at full noise and how much easier does it rev in the upper rev range . You can put up with a little hesitation on low revs if it works that well on the top end , any ideas on what the cam is ?
Author:  hothead115 [ Wed May 30, 2007 5:11 pm ]
Post subject: 
not sure mate, we bought the block rebuilt as a standard cam but it sounds too lumpy and goes too well for it not to be.Oh well we shall find out more tomorrow as she gets dynoed so will post more tomorrow afternoon
Author:  Mick 77 [ Thu May 31, 2007 1:08 pm ]
Post subject: 
Sorry for the hijack, I just got myself a set of 1 3/4 twins without a manifold, can you tell me where to get the Maniflow manifold from and rough costs.

From the positive comments sounds like the maniflow is the way to go.
Author:  Matt68 [ Thu May 31, 2007 1:38 pm ]
Post subject: 
Contact maniflow directly, and don't forget to specify the size carb, the size port you are planning in the head and if you need a throttle cable bracket mount.



They are in the UK, it will cost you around 95 pound for a manifold made to you spec, but it is bloody worth every cent and more.

They are made from mild steel, so will need painting or chrome plating to prevent corrosion... 8) 8)

http://www.maniflow.co.uk
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