ausmini :: View topic - Twin Or Single?

Ive talked to a few people about this, both experts and others, they all are apposed to what you guys are saying, they seem to believe that the only people they know with them are purists and people doing resto's. there arent a lot of people who can tune twins well, and i dont know many either. The cost of rebuilding them seems a bit scarey too......

Quote:

they will use the same amount of fuel, up until the point where they make more power than the other..

i'll dissagree there, it comes down to which units are tuned best and are the most effecient. why can a single throttle SR20DET out-perform a quad throttle SR20DET set up? its all in the development.

If anyone has done such a swap, let me know cheers! (The SU's i mean!)

I would like to bring one point to light: Many people are under the mistaken appregension that twin carbs will use more fuel than a single carb...This is a complete and utter fallacy.

Remember a certain amount of fuel has to mix with a certain amount of air. Within very close limits a set quantity of air is needed to produce a given horsepower. Because fuel/air ratio is virtually fixed, this means a set amount of fuel is needed to make that horsepower to go with the air..

The net result: For a given HP, if all else is equal, the twin-carburetor setup will use no more or less fuel than the single-carb setup...

Twin SU's feed straight into their respective ports; therefore the mixture distribution is better. So for a given horsepower, you actually use lessfuel.

While I am on the subject of arguements against twin carbs, let's look at another one. A lot of people go for the single carb because it's easier to set up, and there are no balancing problems. Many people are afraid of the twin-carb setup because they are not sufficiently knowledgable to be aboe to set the carburetion correctly. They also argue the carburetors "go off tune" too easily - quicker than the single ones. The first arguement won't apply cause somewhere in this chapter I'll tell you how to performance tune SU's, so you'll know how to do it. The second arguement is just one of those old wive's tales. Twin SU's do not "go off tune", unless you have a loose screw somewhere and it physically moves. What happens is the rest of the engion starts to carbon up, wear out; plugs are getting on their last legs, ignition tails off, etc., etc., and the performance of the car deteriorates....

Author:	SnoBall [ Thu Jul 14, 2005 12:21 am ]
Post subject:	Twin Or Single?
I'm thinking of swapping my twin cooper su's for a 1-1/2 single, ive been told the single is 1/2 the trouble and would make the 1100 go better and chew less fuel. any thoughts???

Author:	Mini Mad [ Thu Jul 14, 2005 1:52 am ]
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I would stick with the twins and get them rebuilt and/or properly setup.. There is no reason why a properly set up and recoed set of twins would be any less trouble than the 1.5..The reason alot of twins don't stay in tune is if they're not setup properly or there are worn bushes/linkages etc.. I would say the twins would make more power and I don't think fuel economy would change much unless you have them set up rich.. Depends how you drive..they will use the same amount of fuel, up until the point where they make more power than the other..

Author:	h0nk [ Thu Jul 14, 2005 6:38 am ]
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Roughly how much is it to get twin su's (1 1/4") recoed?

Author:	drmini in aust [ Thu Jul 14, 2005 7:11 am ]
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You will get more torque with the twins. And better up high too. A single 1-1/2" is hardly a ball of fire, although beter than a single 1-1/4"... If the throttle shafts and bodies are not worn, a couple of Fuel Miser repair kits will fix the rest. Sold by Repco, AutoPro, AutoOne etc. Or PM MiniK he got mine cheap, under $20 each! Maybe still can... it's in his sig.

Author:	J_A_M [ Thu Jul 14, 2005 8:33 am ]
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h0nk wrote: Roughly how much is it to get twin su's (1 1/4") recoed? I have just done mine Jet body was $18 (x2) Needle and Seat was $13 (x2) Can of Carby Cleaner was $11 (it's like paint stripper - literally!!) The HS2 carb kits are $30 at Repco, $25 at Pep's Auto. They are a good start. The advice I got for setting up the carbs before fitting these bits was GOLD You need a vernier caliper to set the height of the jet body, then wack it all together. Also, this helps: http://zhome.com/ZCMnL/tech/su.html

ausmini https://www.ausmini.com/forums/

Twin Or Single? https://www.ausmini.com/forums/viewtopic.php?f=2&t=9055	Page 1 of 2

Author:	Wombat [ Thu Jul 14, 2005 12:43 pm ]
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I completely rebuilt a set of twins - rebuild kit from Minispares in England and needles and a couple of bits here - total cost was near $200 but they are like new (included new heat shield)

Author:	SnoBall [ Thu Jul 14, 2005 9:17 pm ]
Post subject:
Ive talked to a few people about this, both experts and others, they all are apposed to what you guys are saying, they seem to believe that the only people they know with them are purists and people doing resto's. there arent a lot of people who can tune twins well, and i dont know many either. The cost of rebuilding them seems a bit scarey too...... Quote: they will use the same amount of fuel, up until the point where they make more power than the other.. i'll dissagree there, it comes down to which units are tuned best and are the most effecient. why can a single throttle SR20DET out-perform a quad throttle SR20DET set up? its all in the development. If anyone has done such a swap, let me know cheers! (The SU's i mean!)

Author:	J_A_M [ Thu Jul 14, 2005 11:06 pm ]
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SnoBall wrote: the only people they know with them are purists drmini a purist?? come on mate....everyone has a different opinion.....gather facts from all corners and make your own opinion based on that info. If a person can tune 1 carb, why couldn't they tune 2 carbs that sit side by side? It's not rocket science......this week was my first endeavour into rebuilding and tuning twins.....and I am amazed at how simple it has been (so far)

Author:	benjamin [ Thu Jul 14, 2005 11:12 pm ]
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in the kitchen

Author:	J_A_M [ Thu Jul 14, 2005 11:20 pm ]
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too cold in the garage at night plus something good was on telly

Author:	Chris [ Fri Jul 15, 2005 12:09 am ]
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SnoBall wrote: i'll dissagree there, it comes down to which units are tuned best and are the most effecient. why can a single throttle SR20DET out-perform a quad throttle SR20DET set up? its all in the development. If anyone has done such a swap, let me know cheers! (The SU's i mean!) Disagree all you want, but on minis two 1 1/4 carbies will work better than one 1 1/2, given good manifolding and tuning. Put an 1 3/4 on it and yes it will be quicker than the 1 1/4's. What's an SR20DET? Is that something that goes to the moon?

Author:	Mini Mad [ Fri Jul 15, 2005 1:42 am ]
Post subject:
SnoBall wrote: Ive talked to a few people about this, both experts and others, they all are apposed to what you guys are saying, they seem to believe that the only people they know with them are purists and people doing resto's. there arent a lot of people who can tune twins well, and i dont know many either. The cost of rebuilding them seems a bit scarey too...... Quote: they will use the same amount of fuel, up until the point where they make more power than the other.. i'll dissagree there, it comes down to which units are tuned best and are the most effecient. why can a single throttle SR20DET out-perform a quad throttle SR20DET set up? its all in the development. If anyone has done such a swap, let me know cheers! (The SU's i mean!) I'm going to quote a bit of Vizard here...: David Vizard wrote: I would like to bring one point to light: Many people are under the mistaken appregension that twin carbs will use more fuel than a single carb...This is a complete and utter fallacy. Remember a certain amount of fuel has to mix with a certain amount of air. Within very close limits a set quantity of air is needed to produce a given horsepower. Because fuel/air ratio is virtually fixed, this means a set amount of fuel is needed to make that horsepower to go with the air.. The net result: For a given HP, if all else is equal, the twin-carburetor setup will use no more or less fuel than the single-carb setup... Which is what I was saying..then he goes on in further detail which i can't be bothered typing or explaining... Also says and i quote: David Vizard wrote: Twin SU's feed straight into their respective ports; therefore the mixture distribution is better. So for a given horsepower, you actually use lessfuel. David Vizard wrote: While I am on the subject of arguements against twin carbs, let's look at another one. A lot of people go for the single carb because it's easier to set up, and there are no balancing problems. Many people are afraid of the twin-carb setup because they are not sufficiently knowledgable to be aboe to set the carburetion correctly. They also argue the carburetors "go off tune" too easily - quicker than the single ones. The first arguement won't apply cause somewhere in this chapter I'll tell you how to performance tune SU's, so you'll know how to do it. The second arguement is just one of those old wive's tales. Twin SU's do not "go off tune", unless you have a loose screw somewhere and it physically moves. What happens is the rest of the engion starts to carbon up, wear out; plugs are getting on their last legs, ignition tails off, etc., etc., and the performance of the car deteriorates.... and it goes on.. Buy the book. Haha Chris..SR20DET is a 2L Nissan motor...and i'm not got to bother discussing it..

Author:	ELMO [ Fri Jul 15, 2005 2:28 am ]
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My 1275 A+ is fitted with a hif44 and minisport manifold but as an OLD guy, I like the bling of twins so I'm rebuilding a set of 1-1/2" and using a minispares ( UK ) manifold. Anton , I missed you at the swap meet, maybe another time soon, but I relate to your carbby rebuild center. Mine though has a ROUND BENCH. Regards Steve E

Author:	drmini in aust [ Fri Jul 15, 2005 7:33 am ]
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I had a single 1-1/2" on Barney (1293)- I recently took it off and fitted twins. It DOES now have more torque now and power all the way up. And I haven't even played with needles, yet. OK, so they are twin HS4s... torque down low would probably be even better with twin HS2s.

Author:	TK [ Fri Jul 15, 2005 10:29 am ]
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Here's one for ya. What are YOUR ideas on what would be better for stock reconditioned 1275? Single HS6 on Graham Russell ported manifold, Ramflow filter or Twin HS2s?????? Power, Torque, Drivability?

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