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single 1/2 or twin 1/4
https://www.ausmini.com/forums/viewtopic.php?f=2&t=12699		 Page 1 of 2
Author:  joel [ Mon Oct 31, 2005 4:53 pm ]
Post subject:  single 1/2 or twin 1/4
im running twin 1/4 su carbis of a cooper s manifold(so im told) would a single 1/2 be better,i seem to use a lot of fuel,i have a 1100+70,xtractors(i think :lol: )
Author:  clubby123 [ Mon Oct 31, 2005 5:07 pm ]
Post subject: 
im running the same su's with LCBs i'm happy with my setup
Author:  willy [ Mon Oct 31, 2005 5:55 pm ]
Post subject: 
Twins and extractors.
But only if the bloody things are tuned properly :twisted:
Shits me seeing too many twin carbies WAY out of tune.
Some people just don't get it.
Author:  poeee [ Mon Oct 31, 2005 6:18 pm ]
Post subject: 
A single 1.75" SU would be better. It's the same size as twin 1.25". 8)

Depends on your engine spec, though.
Author:  drmini in aust [ Mon Oct 31, 2005 6:36 pm ]
Post subject: 
You will get better torque with twins. And although 1x 1.75 might be same as 2x 1.25 in cross section, you are comparing oranges and lemons here. Read Vizard... p(TBA). :wink:

<edit> I'm still looking for the page, but basically the airflow thru a single carb is continuous- but with twins it's intermittent- each carb is sucking for 1/2 the time. (eg cyl 3 sucks, then 4- but during this same time interval the intake valves on cyls 1 & 2 are closed).
Author:  kazjim [ Mon Oct 31, 2005 6:42 pm ]
Post subject: 
Doc, P75 in the 3rd edition.. i think you mean.....

Although P135/6 also discusses the Twin-carb manifold......

Bookworm J
Author:  LS1380 [ Mon Oct 31, 2005 8:17 pm ]
Post subject: 
I'm running with twin 1 3/4 SU's with Maniflow inlet manifold match ported to the head....
Then dyno-tuned and rejetted.The difference from twin 1 1/2 to 1 3/4 is unbelievable.
Torque and HP all increased,and now rev's out without any hesitation. I now really believe
that after you think you have the SU's tuned at home-take it to a GOOD Dyno-Tuner.
It is well worth the extra dollars :D :D
Author:  kazjim [ Mon Oct 31, 2005 8:27 pm ]
Post subject: 
Sorry Doc, Bottom Left of page 134.....

"On a Twin-carb setup, when one cylinder draws, it does not draw on 240cfm of airflow capability, it draws on the 120CFM of one carb....." et al.

J
Author:  drmini in aust [ Mon Oct 31, 2005 8:38 pm ]
Post subject: 
Thanx James, that's the one I wanted... :wink:
Main reason you get more low down torque from twins is the airflow into the ports is more direct. So they say...

re. carb sizes- I've had 34, 36, & 38mm chokes in the 45 Dellorto on my 1360. With the 38s, it is better than 36s all the way up to 7500+. And it'll still pull 4th gear clean from 1500 at part throttle. 8)
Author:  LS1380 [ Mon Oct 31, 2005 9:00 pm ]
Post subject: 
drmini in aust wrote:
Thanx James, that's the one I wanted... :wink:
Main reason you get more low down torque from twins is the airflow into the ports is more direct. So they say...

re. carb sizes- I've had 34, 36, & 38mm chokes in the 45 Dellorto on my 1360. With the 38s, it is better than 36s all the way up to 7500+. And it'll still pull 4th gear clean from 1500 at part throttle. 8)

You've got me thinking about 4th gear at 1500rpm.What speed would you be doing,when
you do this :?: At the moment anything under 60k's in 4th is a No-Go,and need to change down to 3rd to get things moving along :!: :!:
Author:  drmini in aust [ Mon Oct 31, 2005 10:13 pm ]
Post subject: 
I'm running a 3.647 diff. Pulled the 3.44 out to get even more acceleration in 4th gear... :P
1500 is around 23mph. x 1.62 to get bloody KMH... :lol:
Author:  LS1380 [ Mon Oct 31, 2005 10:29 pm ]
Post subject: 
Hmmmm-Very interesting :!:
What are you reving out to in 3rd gear.ie speed wise(max) and what rev's :?: :roll:
Author:  drmini in aust [ Tue Nov 01, 2005 5:55 am ]
Post subject: 
I used to upshift the old 1310 at 7500 in 3rd... with a 3.44 diff that's about 90MPH I think.
It would go further but no point really.

With he new 1360 motor, I'll observe the same rev limit. The old MK1 S crank is on it's 40th birthday.. 8)

I used to see 95MPH at the end of the straight at Wakefield Pk, with more urge in 4th now it should be a few knots quicker.
Author:  J_A_M [ Tue Nov 01, 2005 7:59 am ]
Post subject: 
Joel, forget changing your carbs....just pay a decent Mini mechanic to tune it.

I will be taking mine to Greig (Mini Classic) soon for a dyno tune. Your's probably needs the same. IMHO, that's the best way to tune a car.
Author:  LS1380 [ Tue Nov 01, 2005 8:49 am ]
Post subject: 
With he new 1360 motor, I'll observe the same rev limit. The old MK1 S crank is on it's 40th birthday.. 8)

Thanks Doc-With 3.4 diff and 12inch wheels,things are a lot different 8) 8)
Geez-your crank is doing very well.Are the Mains and Bigends still standard,or are you on your last grind?
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