I had read somewhere that multiple carbs generally produced better torque and got to a comparable top end.
Maybe vizard is talking about race use where low down performance doesn't matter so much. Or I'm just wrong
I don't know from experience so I can't really say.
I just figured that was why coopers had 2...

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

it's across the board.... you look through any of the UK mini mags, all the really hot road cars are running a single HIF 44, the only ones with twins do it for the retro styling.

A single theoretically works better on a road motor because A series motors work with 2 pulses down each intake port in sequence, our firing order is 1,3,4,2 - continue that on as 1,3,4,2,1,3,4,2,1,3,4,2 and the pattern emerges that we do an intake on 2, and 1, then on 3 and 4. If you think about it that way, then twins are funny because each one will get 2 sucks, then rest for 2 sucks, then 2 sucks, then rest for 2 sucks etc. etc. and the inertial flow through each throat is disrupted as it goes from suck, suck to rest, rest, suck, suck to rest, rest. If you use a big single then the inertial flow is constant, suck suck suck suck suck - the air is always moving through the carb. The traditional percieved benefit of twins is that they have a straight shot down the port, in practise, having a straight shot is outweighed by a lot of other factors....

that's part of what Vizard discusses

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Current thinking (according to KC on MM forum) is that the Cooper etc twin SU manifold is a POS, the balance pipe is too big and poorly positioned. So it interferes with the airflow. Putting a radius inside like Vizard said, helps but doesn't fix the problem.
I'm putting twin HS4s on Barney's 1293- the balance pipe will be filled with epoxy then redrilled smaller.

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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.

Makes sense I had read the suck suck thing from a link Kev posted about trying to fuel inject an A series but I had never connected it to carbs and twin carbs in particular.

I haven't got Vizards book so I hadn't read that...

Cheers, Arrin

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

i think the main thing is that by now most mini carbs will not be in great condition, and combine that with 2 carbs, and it equals twice the fiddling and adjusting to get old tired carbs to run right.

unless you wanna throw money at it.[/u]

um a weber is effectively two carbs in the one body by that theory so each barrel wouls suffer from your suckworthy theory too

michael

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

i dont like webers, they're harder to get, more expensive, you have to cut the firewall, loud and don't give enough extra performance over a s.u to be worth it for road use and they guzzle fuel

Weber or Dellorto has no balance pipe. No need....
I was told once that the real reason twin SUs have one is to prevent fluttering of the piston when attached to a siamese port on a 4 cylinder motor.
Firing order of a Mini is 1-3-4-2-1-3-4-2 etc
So you can see #2 sucks on the port then #1, then there is an equal time during which #3 and #4 do the same. During this period there is no suction in the 1-2 inlet port, if no balance tube the SU's piston could drop..

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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.

good point. yeah on that basis i reckon your theory of a smaller "balance" pipe diameter would work, but you might need to play with it a bit to find the ideal. all you need to do is maintain the pressure (vacuum)? i'll have to pull the SU apart again to remember how it all works. i could look at a drawing, but nothing like holding the thing in your hand

michael

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

The standard one is bloody near 1" in diameter. What I'll do is remove end plugs, fill it up, drill a 1/2" hole up it and work up from there.
Might be able to use a bit of plastic tube inside instead of epoxy.

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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.

Aren't you a welder? Why not make a manifold from scratch. Much more bragging rights there

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

I've made manifolds before- last one 1968! Twin Amal Monoblocs on a 15* angle, motor was a 1098 bored to 1220 with a 544 cam. 1100S head..
Too lazy nowadays! Easier to just buy one. My Russell Engineering DCOE one I bought as a bare casting and milled it up.

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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.

what oversize was the 1098 to get 1220? How did that one go?

got one i have to rebuild for the mini minor. it had a 45 dellorto on it, so i'm curious as to what is going on inside. i already know the 12G202 has double valve springs. i'm not lazy enough to buy an engine already built yet or rich enough

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

Ther is a reason why BMC used twin 1 1/4" SU's on their performance cars.
They spent millions of dollars on R&D to come up with this package.
Obviously if a single carb was better they would have done it?

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Did 16s 1/4M at Castlereagh Dragstrip back then.
Offset bored it to 68.0mm for Imp pistons, decked the block .140" then notched it for the exhaust valves (12G940 head).
Went like crap off a shovel for 20,000 miles, until it broke a piston circlip and the pin scored #3 bore. Too many revs- I used to buzz it to 8500
1098 crank survived but it had 8 little cracks in it when I pulled it down. Hung it on the wall next to the busted 850 one..

I've built a couple of 1220s since (Sprite motors) but now I use Teflon buttons not circlips.

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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.