John P
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| posted on 23/11/05 at 01:59 PM |
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SU Carbs
May seem crazy but has anybody considered fitting SU carbs to a modern (Zetec 2.0) engine?
I've used an ex Mini 1 1/4" SU on a vintage car and it worked really well without modification to jet or needle, presumably because it
effectively adjusts itself in response to the vacuum in the induction system.
SU's are available very cheaply at autojumbles and boot-fairs and fitting say 4 off 1 1/2" units would not appear to be inpossible.
I know it would be easier to go for Bike Carbs or save up for twin DCOE's but I fancy trying something new unless there a good reason why it
won't work.
Any feedback would be welcome.
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NS Dev
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| posted on 23/11/05 at 02:11 PM |
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SU carbs are used quite a lot in autograss racing on various more modern engines, though I have never seen them on a Zetec etc.
Plenty used on the vauxhall 8 valve engines in class 2 cars where only one barrel of induction is allowed.
You might be pushing your luck on flow rates on a zetec though, you will probably find that you need to make a twin carb manifold that allows all 4
cyls to draw from both carbs, which will not be easy to do!
If 1 carb per 2 cls is ok then one like this would do:
[Edited on 23/11/05 by NS Dev]
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mookaloid
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| posted on 23/11/05 at 03:31 PM |
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have a look at Jacko's archive
example: http://www.locostbuilders.co.uk/photos.php?action=showphoto&photo=Imgp1504.jpg
Cheers
Mark
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britishtrident
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| posted on 23/11/05 at 03:49 PM |
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A single SU is fine almost perfect simple form of carburation --- but a pair are a pain in the neck, while triple as on the E Type were b****** to
set up.
One SU per cylinder dosen't work well , the heavy piston gets pulsed up and down like crazy which is why it was never used in the 50s and
60s.
So you would need to use a pair with a balance tube.
With the old Lotus 1558cc wincam engine the Twin Stromberg head was about 15 -20 hp down on the the Weber DCOE /Dellotro engine with the same SSE
cams.
[Edited on 23/11/05 by britishtrident]
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jacko
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| posted on 23/11/05 at 06:51 PM |
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su carbs
John P - As Mookaloid said I made my own manifold to take two 1" 3/4 su's from metro 1300cc. Ive used them for 2 summers now with great
success. As you say they are quiet cheap to pick up at scrap yards etc. I am now in the process of making a manifold to take ZX9R carbs to see if I
can get more bhp out of the engine The only problem I found with the su's was a flat spot at 4000 revs which ive tried to rectify maybe a
rolling road would have sorted this. All the best Jacko
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Bob C
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| posted on 23/11/05 at 10:49 PM |
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I've got a pair of old rover V8 SUs if anyone wants 'em.
These are the really old ones where the choke works by heaving the entire float chambers up & down. I can't remember the diam but someone on
here will know.
Bob C
PS - SU stands for "skinner union" - nothing technical whatsoever!
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02GF74
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| posted on 24/11/05 at 09:39 AM |
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quote:
Originally posted by Bob C
I've got a pair of old rover V8 SUs if anyone wants 'em.
These are the really old ones where the choke works by heaving the entire float chambers up & down. I can't remember the diam but someone on
here will know.
Bob C
PS - SU stands for "skinner union" - nothing technical whatsoever!
Rover v8 would have had 1 3/4 inch SU. The ones you describe sound like HS types (model HS 6).
Whilst there is nothing wrong with them, the separate float chamber will take up more space than if you went with a pair of HIF 6. These superceded
the HS and have float chamber as part of the main body - they are also better on slopes plus have additional enhancements.
I'd be surprised if you would have space to fit 4 carbs. I am not sure if feeding one cylinder per carb is a problem as I'm pretty sure I
have seen Harleys fitted with twin SUs. Balance is an issue for idling.
You can fine tune them by fitting different needles - there's loads to choose from and profile data is readily available but to get optimum
performance would need a trip to the rolling road - same as for any carb really.
Jacko's set up is interesting as he is using carbs of the same handness - not the way I would do it.
You can get SUs in both left and right handed bodies so can fit linkages for choke and throttle a bit easier although Jacko seems to have done it
somehow.
[Edited on 24/11/05 by 02GF74]
[Edited on 24/11/05 by 02GF74]
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NS Dev
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| posted on 24/11/05 at 12:54 PM |
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The problem that I was getting at when talking about trying to feed all 4 cyls from both of a pair of carbs is that the carbs will be a bit limited in
terms of airflow.
On a fairly docile 2ltr pinto that should be no problem, but could be on a 170hp zetec!
You have to remember that a single carb or twin carb setup is exactly the same as far as the engine is concerned in terms of airflow "per
cylinder" i.e. each cylinder still only draws through the one carb.
The rover v8 setup is different as it draws all cyls from both carbs.
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John P
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| posted on 24/11/05 at 01:22 PM |
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SU Carbs on Zetec
Jacko,
Do you know what sort of power your getting from your twin SU set up?
John.
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