Single to Twin SU Worth It?

General Chat with an emphasis on BMC Minis & Other iconic cars of the 1960's. Includes information on MK1 Action days.
Tornado99
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Single to Twin SU Worth It?

Post by Tornado99 »

I have an '88 Mini with a 1275cc engine, unknown internal mods (maybe a hot cam as some local Mini mechanics suggested). Has a single HSU4 carb with stock manifold and K&N gauze intake filter.

Is there much to be gained by converting to a twin SU setup? If so, what carb size should I be looking for?
Thanks.
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timmy201
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Re: Single to Twin SU Worth It?

Post by timmy201 »

Depending on the modifications to the engine you might be better off with a single 1.75” carb

If you wanted twin SU carbs then for a relatively tame engine you’d pick twin 1.25” carbs, and for highly tuned 1275 engines you’d pick twin 1.5” carbs

Regardless of the direction you chose, you need to have good condition carbs that are matched, built correctly and tuned for the performance of your particular engine
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Exminiman
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Re: Single to Twin SU Worth It?

Post by Exminiman »

Suppose question is what do you want to use the car for…..fast road, competition ?

If its road? and you are not concerned about every last HP, then I would stick with the single SU and a decent manifold

Single SU is smoother, easier to set up………….and cheaper :D
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johnv
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Re: Single to Twin SU Worth It?

Post by johnv »

But twins look soooo much better...
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Tornado99
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Re: Single to Twin SU Worth It?

Post by Tornado99 »

Exminiman wrote: Thu Mar 02, 2023 6:39 am Suppose question is what do you want to use the car for…..fast road, competition ?

If its road? and you are not concerned about every last HP, then I would stick with the single SU and a decent manifold

Single SU is smoother, easier to set up………….and cheaper :D
Ya not looking for top power and performance. It is a street car to ride about in for fun.
I have a classic motorcycle that I converted from single to dual carb and found bike much more lively in mid range, so got me thinking the cooper S setups might be worthwhile. I use a dual vacuum guage setup to balance my bike carbs and a colortune to help with setting mixture. Are these used on dual carb mini tunes?
Cheeser
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Re: Single to Twin SU Worth It?

Post by Cheeser »

For your use I would suggest single HIF 44 on good inlet with proper air filter. Once that is sorted get it set up on a rolling road by someone who knows about SUs.
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mk1
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Re: Single to Twin SU Worth It?

Post by mk1 »

Couldn't agree more with Cheeser.

The HIF44 is a very good carb & you are unlikely to be able to detect any improvement using twin HS2's over an HIF44 on a decent manifold. The single is cheaper, easier & will stay in tune longer.

If all you are bothered about is decent reliable performance, then the HIF is the way to go, if you want something that goes about the same but looks much "cooler" then twins is a great option. But they will cost more than twice as much be less reliable & will certainly go off tune fairly frequently.

As ha salso been said, whatever option you go for an initial dyno session is essential.
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UHR850
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Re: Single to Twin SU Worth It?

Post by UHR850 »

I had a Hif44 carb on my MG Metro engine but changed it to a twin Hs2 setup. I was not happy with that so did put the Hif44 back on it, happy again.
DOWNTON Mini is what I like a lot.
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Peter Laidler
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Re: Single to Twin SU Worth It?

Post by Peter Laidler »

I am like you Tornado. I use a colourtune to set my mixtures. but I use my sensitive ears and stethescope to set the air intake.

Nothing wrong with a refurbished - or known good - HIF44

What is your classic bike? Me too......
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tweedy998
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Re: Single to Twin SU Worth It?

Post by tweedy998 »

I'd probably echo what others have said and in your case suggest sticking with a single, probably a HIF 44.

Twins do look very aesthetically pleasing, but do need quite a lot of things to be right, are quite high maintenance and expensive, as others have highlighted.
1965 Tweed Grey Mk1 Morris Cooper 998
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