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 )

im running the same su's with LCBs i'm happy with my setup

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Twins and extractors.
But only if the bloody things are tuned properly
Shits me seeing too many twin carbies WAY out of tune.
Some people just don't get it.

A single 1.75" SU would be better. It's the same size as twin 1.25".

Depends on your engine spec, though.

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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).

<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).

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Doc, P75 in the 3rd edition.. i think you mean.....

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

Bookworm J

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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

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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

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Thanx James, that's the one I wanted...
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.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

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

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I'm running a 3.647 diff. Pulled the 3.44 out to get even more acceleration in 4th gear...
1500 is around 23mph. x 1.62 to get bloody KMH...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hmmmm-Very interesting
What are you reving out to in 3rd gear.ie speed wise(max) and what rev's

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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..

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.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

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.

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

Thanks Doc-With 3.4 diff and 12inch wheels,things are a lot different
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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