hey guys

just after some advice on carbies, i am in need of upgrading my old 1 1/2' as i hav had ongoing problems with it. i am looking into twin 1 3/4 SUs, assuming that they are bigger are they the best performance wise? i have a rebuilt 1275cc engine.

what is the primary comparison between Webers and SUs??

Thanks

I thought this was about Veterans cutting their Viagra tabs in half

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Carbs on their own will not give you any extra performance. All they will do is give you the potential to have more performance.

The performance gained is in the manifold.
So whatever carb you use dont bung it on a dodgy manifold.

And twin 1 3/4s would be a bit big for a stock 1275.

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Simplify and add lightness

but will it increase the power if i am upgrading from a single to a twin setup?

best bet would be the standard twin 1 1/4's, or if your head has had enough work done to it, twin 1 1/2's.... that'll get it up and going...

twin 1 3/4's are a little too big for a daily car, more left for the fully fledged track eaters...

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Planet Earth is blue and there's nothing I can do...



“A turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.” - Jeremy Clarkson

It depends on the intake manifold.

If you have a single on a really well flowing manifold, then put the twins on a cheapy chinese manifold you lose power and drivability.

Likewise if your using a stock single inlet manifold and upgrade to a twin carb performance one you will see more power.
But it wont be because of the extra carb.

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Simplify and add lightness

assuming your primary consideration is performance?

what other work has been done to the motor? or what are you planning?

Why has no one mentioned weber/dellorto? Carbies of kings...

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Yeah, I would agree... twin 1 3/4" probably a bit full on for a roadie..

The manifold does come into play a bit (but so does the head and rest of the motor and where and how you will be driving it most of the time), you want one that meets the demands of the motor, if it doesn't flow enough then you just rob yourself of potential power the whole way up the rev range but particularly as you reach the top.

As far as differences between Webers and SU's, well, the difference between a HIF44 and a 45DCOE is that (if everything is in order) you might get an extra 5hp out of a weber at the top end of the rev range... but with an SU, you will get more torque at lower rpm...

Webers can be tuned to run economically, but even so they are thirster than an SU... but they do sound awesome

For a hot 1275 for the road I would suggest maybe a set 2X1 1/4" SU's, a HIF44 or 2X1 1/2" SU's...

But as was pointed out by Gareth_1330,, it depends on what has been done to the motor

well i havnt heard to much difference between the webers/dellortos to SUs

but an extra 5hp doesnt justify modifying the firewall...

the engine has an oversized cam with electronic dizzy rebored to 1310cc has been runny badly since built because of the carby and want this justified finally only thing is which way to swing

they used HIF44's on everything from the high compresion 998 Metro HLE thru to the Metro Turbo,, so I reckon for a roadie that they are a safe bet...

As far as far as manifolds for them go, I normaly use the MG Metro manifold as they perform better than some of the after market ones. But they are getting hard to find.

What ever you settle on, get the car dyno tuned or you wil never get the most out of it

Single 1 1/2 or 1 3/4 if its a stock 1275!!!!

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I agree with some reservation.

I just love the sight of a couple of big jugs!

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Big single 1 3/4 works well & is easy to tune, at a much better cost than twins.

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Too many cars, and too little time.

thanks guys

the guys running SUs have you had running problems and problems tunning?

If an SU of any type is in good condition and set up properly for the motor its on, it will run fine. Getting said carb set up shouldn't be a major drama. Twins are a bit more involved but the same applies. What problems are you having with your HS4?

cheers

Kevin