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PostPosted: Wed Feb 22, 2012 5:48 pm 
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848cc
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Location: Adelaide S.A
i have another bizare idea

FIRST, my bmw e36 has a dual runner length intake;
long: low rpm torque, short: high rpm
it also has two throttle body valves, large 54mm and small 35mm

ALSO some weber downdrafts have dual throttle valves 32mm and 36mm

in both examples the small valve opens first providing better fuel economy then at aprox 20% throttle the second valve opens giving more air for high rpm

ok heres the idea twin HS4 34mm or HS6 44mm carbs located close to the head via straight piping and short trumpets, inline with the ports (mass air flow, for high rpm).
Piped to a long length into the same "complex" manifold i have a hs2 32mm that opens first feeding both ports

Because all the carbs are self ajusting according to air intake vacume the bottom carbs will only open if required regardless of throttle valve! or have i got su's all wrong (kinda still self teaching my self about su carbs)

what would the out come be factoring any combination of cam valve lift and size, on a 1330cc or more

_________________
1969 Blue Mini K, 1330cc, Weber 45, polished aluminum roll cage, Race seats, 4 point harness, full rewire incorporating 8 fuses, 6 relays and new headlights :) just needs tyres front shocks and a windscreen til re-register


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PostPosted: Wed Feb 22, 2012 6:16 pm 
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An SU carb `resizes itself' by lifting the piston in responce to the airflow required.
Even an HS6 can give good low speed tractability, as the piston doesn't lift far under these conditions.
What you propose has some merit with fixed venturi carbs, but with SUs I believe it will just add complication, not power.
[edit] Progressive twin choke carbs eg Weber are a poor attempt to achieve what an SU does with its 1 variable choke.

BTW I do like Webers, but not the progressive ones (been there in a pre-Mini life with an Italian Love Affair). :wink:
Weber 45DCOEs, (and Dellorto 45 DHLAs)- now you're talking... :P

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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. :mrgreen:


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PostPosted: Wed Feb 22, 2012 6:26 pm 
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848cc
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Location: Adelaide S.A
ok, so tractability is good in SU's so they deveat the purpose of dual throttle valves,
and because webers are fixed jetted it utilises dual TV to make them more tractible.

is that right?

if i made dual length runners that run off One or Two carbs, could i get incresed torque without sacrificing top end?

_________________
1969 Blue Mini K, 1330cc, Weber 45, polished aluminum roll cage, Race seats, 4 point harness, full rewire incorporating 8 fuses, 6 relays and new headlights :) just needs tyres front shocks and a windscreen til re-register


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PostPosted: Wed Feb 22, 2012 7:08 pm 
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A Mini doesn't have enough intake ports to utilize dual length runners per port properly- as the intake strokes of cylinder 3-4 and 1-2 overlap. This allows charge robbing between cylinders.
There is also bugger all room with the carbs at the back.
The stock intake runners are too short for both max power and torque, hence why racers fit a Weber with long runners (5"-6" or even longer) and the carby back (almost) in the cabin.
If you want max NA torque AND power for street use I would fit a 7 or 8 port head first. Then, with 1 port per cylinder, you can play with variable length runners. But personally if I had one, I'd be fitting either twin Webers/Dellortos, or MPI.

[edit] See the torque figure (112ft/lb) for my 1412 stroker in my sig below- this was achieved with a single HS6 on a Russell Engineering RE7 SU manifold.

_________________
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. :mrgreen:


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PostPosted: Thu Feb 23, 2012 3:12 pm 
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848cc
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Joined: Sun Nov 02, 2008 9:04 am
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Location: Adelaide S.A
yeah my webers prodrude through the firewall at the moment, but ive been forced to change to a 1098 and i have a hs2 hs4 and hs6, and all that room from the airbox cut into the firewall so ive got a bit of space to play with, thankyou for being so helpful,

as time goes on i see many engine changes and improvements if anything that helps modern cars run better could help my car, ill ask here.
i know you guys are wiser than me, and have tryed many things, but so many inventions come out each year we smack our selves in the head thinking "its so obvious why diddent i do that", a fresh mind and a wise one will go further than each by them selves :)

_________________
1969 Blue Mini K, 1330cc, Weber 45, polished aluminum roll cage, Race seats, 4 point harness, full rewire incorporating 8 fuses, 6 relays and new headlights :) just needs tyres front shocks and a windscreen til re-register


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